Datasheet AD5757 Datasheet (ANALOG DEVICES)

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Quad Channel, 16-Bit,

Serial Input, 4 mA to 20 mA Output DAC,

Dynamic Power Control, HART Connectivity

Data Sheet

FEATURES

16-bit resolution and monotonicity Dynamic power control for thermal management

or external PMOS mode

Current output ranges: 0 mA to 20 mA, 4 mA to 20 mA,

or 0 mA to 24 mA

±0.05% total unadjusted error (TUE) maximum User programmable offset and gain On-chip diagnostics On-chip reference (±10 ppm/°C maximum)

−40°C to +105°C temperature range

APPLICATIONS

Process control Actuator control PLCs HART network connectivity

GENERAL DESCRIPTION

The AD5757 is a quad, current output DAC that operates with a power supply range from 10.8 V to 33 V. On-chip dynamic power control minimizes package power dissipation by regulating the voltage on the output driver from 7.4 V to 29.5 V using

AD5757

a dc-to-dc boost converter optimized for minimum on-chip power dissipation.

Each channel has a corresponding CHART pin so that HART signals can be coupled onto the current output of the AD5757.

The part uses a versatile 3-wire serial interface that operates at clock rates of up to 30 MHz and is compatible with standard SPI, QSPI™, MICROWIRE™, DSP, and microcontroller interface standards. The interface also features optional CRC-8 packet error checking, as well as a watchdog timer that monitors activity on the interface.

PRODUCT HIGHLIGHTS

1. Dynamic power control for thermal management.

2. 16-bit performance.

3. Multichannel.

4. HART compliant.

COMPANION PRODUCTS

Product Family: AD5755-1, AD5755 External References: ADR445, ADR02 Digital Isolators: ADuM1410, ADuM1411 Power: ADP2302, ADP2303

Additional companion products on the AD5757 product page

FUNCTIONAL BLOCK DIAGRAM

+15V

AGND

DGND

LDAC

SCLK

SDIN

SYNC

SDO

CLEAR

FAULT

ALERT

AD1

AD0

REFOUT

REFIN

NOTES

1. x = A, B, C, AND D.

Rev. B

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners.

DIGIT AL

INTERFACE

REFERENCE

AD5757

GAIN REG A

OFFSET REG A

DAC CHANNEL A

DAC CHANNEL B

DAC CHANNEL C

DAC CHANNEL D

5.0V

DC-TO-DC

CONVERTER

DAC A

CURRENT AND

OUTPUT RANGE

BOOST_x

7.4V TO 29.5V

VOLTAGE

SCALING

OUT_x

SET_x

CHARTx

09225-101

Figure 1.

AD5757 Data Sheet

Features.............................................................................................. 1

Applications....................................................................................... 1

General Description ......................................................................... 1

Product Highlights ........................................................................... 1

Companion Products....................................................................... 1

Functional Block Diagram .............................................................. 1

Revision History ............................................................................... 3

Detailed Functional Block Diagram .............................................. 4

Specifications..................................................................................... 5

AC Performance Characteristics ................................................ 7

Timing Characteristics ................................................................ 7

Absolute Maximum Ratings.......................................................... 10

ESD Caution................................................................................ 10

Pin Configuration and Function Descriptions........................... 11

Typical Performance Characteristics ........................................... 14

Current Outputs ......................................................................... 14

DC-to-DC Block......................................................................... 19

Reference ..................................................................................... 20

General......................................................................................... 21

Terminology .................................................................................... 22

Theory of Operation ...................................................................... 23

DAC Architecture....................................................................... 23

Power-On State of the AD5757 ................................................23

Serial Interface ............................................................................ 23

Transfer Function....................................................................... 24

Registers........................................................................................... 25

Programming Sequence to Write/Enable the Output

Correctly ...................................................................................... 26

Changing and Reprogramming the Range ............................. 26

Data Registers ............................................................................. 27



Control Registers........................................................................ 29

Readback Operation .................................................................. 32

Device Features............................................................................... 34

Output Fault................................................................................ 34

Digital Offset and Gain Control............................................... 34

Status Readback During a Write .............................................. 34

Asynchronous Clear................................................................... 34

Packet Error Checking............................................................... 34

Watchdog Timer......................................................................... 35

Output Alert................................................................................ 35

Internal Reference...................................................................... 35

External Current Setting Resistor ............................................ 35

HART........................................................................................... 35

Digital Slew Rate Control.......................................................... 36

Power Dissipation Control........................................................ 36

DC-to-DC Converters............................................................... 36

AICC Supply Requirements—Static .......................................... 38

AICC Supply Requirements—Slewing ...................................... 38

External PMOS Mode................................................................ 39

Applications Information.............................................................. 40

Current Output Mode with Internal R

Precision Voltage Reference Selection..................................... 40

Driving Inductive Loads............................................................ 40

Transient Voltage Protection .................................................... 41

Microprocessor Interfacing....................................................... 41

Layout Guidelines....................................................................... 41

Galvanically Isolated Interface ................................................. 42

Outline Dimensions....................................................................... 43

Ordering Guide .......................................................................... 43

................................ 40

SET

Rev. B | Page 2 of 44

Data Sheet AD5757

REVISION HISTORY

11/11—Rev. A to Rev. B

Change to Test Conditions/Comments of Accuracy (External R

) Parameter, Table 1....................................................................5

SET

Changes to Figure 4...........................................................................8

Changes to Figure 5...........................................................................9

Change to Pin 8 Description, Table 5 ...........................................11

Change to Figure 13........................................................................14

Change to Figure 20........................................................................16

Changes to Figure 48 and Power-On State of the AD5757

Section ..............................................................................................23

Change to Table 16 ..........................................................................29

Changes to Readback Operation Section, Readback Example

Section, and Table 25 ......................................................................32

Change to Figure 54........................................................................35

Change to Figure 58 Caption.........................................................38

Changes to Figure 59, Figure 60, and Figure 61 Captions.........39

Changes to Transient Voltage Protection Section and

Figure 63...........................................................................................41

Changes to Galvanically Isolated Interface Section....................42

5/11—Rev. 0 to Rev. A

Changes Features Section.................................................................1

Changes to Figure 2 ..........................................................................3

Changed AV

Min Parameter from 10.8 V to 9 V......................5

Changes to Pin 22, Pin31, Pin 49 Descriptions...........................11

Changes to Pin 58 Descriptions....................................................12

Changes to Figure 8, Figure 9, and Figure 10.............................. 13

Added Figure 23, Renumbered Sequentially...............................15

Added Figure 29..............................................................................16

Added External PMOS Mode Section and Figure 62.................38

4/11—Revision 0: Initial Version

Rev. B | Page 3 of 44

AD5757 Data Sheet

DETAILED FUNCTIONAL BLOCK DIAGRAM

5.0V

AV +15V

BOOST_ A

AGND

DGND

LDAC

CLEAR

SCLK

SYNC

FAULT

ALERT

REFOUT

REFIN

SDIN

SDO

AD1

AD0

POWER-ON

RESET

INPUT SHIFT

AND

CONTROL

STATUS

WATCHDOG

TIMER

(SPI ACTIVITY)

VREF

REFERENCE

BUFFERS

AD5757

INPUT REG A

GAIN REG A

OFFSET REG A

DAC CHANNEL A

DAC CHANNEL B

DAC CHANNEL C

DAC CHANNEL D

DC-TO- DC

CONVERTER

POWER

CONTRO L

DAC

REG A

DAC A

SWB, SWC, SW

7.4V TO 29. 5V

R2 R3

SEN1VSEN2

REG

BOOST_ B,VBOOST_C,VBOOST_ D

OUT_A

SET_A

CHARTA

, I

SET_B

OUT_C

, R

SET_C

, I

OUT_D

, R

SET_D

OUT_B

CHARTB, CHARTC, CHARTD

09225-001

Figure 2.

Rev. B | Page 4 of 44

Data Sheet AD5757

SPECIFICATIONS

AVDD = V REFIN = 5 V; R

Table 1.

Parameter1 Min Typ Max Unit Test Conditions/Comments

CURRENT OUTPUT

Output Current Ranges 0 24 mA

0 20 mA 4 20 mA

Resolution 16 Bits

ACCURACY (EXTERNAL R

Total Unadjusted Error (TUE)

−0.05 ±0.009 +0.05 % FSR TUE Long-Term Stability 100 ppm FSR Drift after 1000 hours, TJ = 150°C Relative Accuracy (INL) −0.006 +0.006 % FSR Differential Nonlinearity (DNL) −1 +1 LSB Guaranteed monotonic Offset Error −0.05 ±0.005 +0.05 % FSR Offset Error Drift2 ±4 ppm FSR/°C Gain Error −0.05 ±0.004 +0.05 % FSR Gain TC2 ±3 ppm FSR/°C Full-Scale Error −0.05 ±0.008 +0.05 % FSR Full-Scale TC2 ±5 ppm FSR/°C DC Crosstalk 0.0005 % FSR External R

ACCURACY (INTERNAL R

Total Unadjusted Error (TUE)

−0.11 ±0.009 +0.11 % FSR TA = 25°C TUE Long-Term Stability 180 ppm FSR Drift after 1000 hours, TJ = 150°C Relative Accuracy (INL) −0.006 +0.006 % FSR

−0.004 +0.004 % FSR TA = 25°C Differential Nonlinearity (DNL) −1 +1 LSB Guaranteed monotonic Offset Error

−0.04 ±0.007 +0.04 % FSR TA = 25°C Offset Error Drift2 ±6 ppm FSR/°C Gain Error −0.12 +0.12 % FSR

−0.06 ±0.002 +0.06 % FSR TA = 25°C Gain TC2 ±9 ppm FSR/°C Full-Scale Error

−0.1 ±0.007 +0.1 % FSR TA = 25°C Full-Scale TC2 ±14 ppm FSR/°C DC Crosstalk4 −0.011 % FSR Internal R

OUTPUT CHARACTERISTICS2

Current Loop Compliance Voltage V

Output Current Drift vs. Time Drift after 1000 hours, ¾ scale output, TJ = 150°C 90 ppm FSR External R 140 ppm FSR Internal R Resistive Load 1000 Ω The dc-to-dc converter has been characterized

Output Impedance 100 MΩ DC PSRR 0.02 1 μA/V

REFERENCE INPUT/OUTPUT

Reference Input2

Reference Input Voltage 4.95 5 5.05 V For specified performance DC Input Impedance 45 150 MΩ

= 15 V; DVDD = 2.7 V to 5.5 V; AVCC = 4.5 V to 5.5 V; dc-to-dc converter disabled; AGND = DGND = GNDSWx = 0 V;

BOOST_x

= 300 Ω; all specifications T

)

SET

MIN

to T

, unless otherwise noted.

MAX

Assumes ideal resistor; see the External Current Setting Resistor section for more information

SET

)

SET

3, 4

−0.14 +0.14 % FSR

3, 4

−0.05 +0.05 % FSR

3, 4

−0.14 +0.14 % FSR

SET

−

BOOST_x

2.4

BOOST_x

2.7

SET

with a maximum load of 1 kΩ, chosen such that compliance is not exceeded; see Figure 31 DC-DC MaxV

bits in Table 24

and

Rev. B | Page 5 of 44

AD5757 Data Sheet

Parameter1 Min Typ Max Unit Test Conditions/Comments

Reference Output

Output Voltage 4.995 5 5.005 V TA = 25°C Reference TC2 −10 ±5 +10 ppm/°C Output Noise (0.1 Hz to 10 Hz)2 7 μV p-p Noise Spectral Density2 100 nV/√Hz At 10 kHz Output Voltage Drift vs. Time2 180 ppm Drift after 1000 hours, TJ = 150°C Capacitive Load2 1000 nF Load Current 9 mA

Short-Circuit Current 10 mA Line Regulation2 3 ppm/V

Load Regulation2 95 ppm/mA Thermal Hysteresis2 160 ppm First temperature cycle

5 ppm Second temperature cycle

DC-TO-DC

Switch

Switch On Resistance 0.425 Ω Switch Leakage Current 10 nA Peak Current Limit 0.8 A

Oscillator

Oscillator Frequency 11.5 13 14.5 MHz This oscillator is divided down to give the dc-to-dc

Maximum Duty Cycle 89.6 % At 410 kHz dc-to-dc switching frequency

DIGITAL INPUTS2 JEDEC compliant

VIH, Input High Voltage 2 V VIL, Input Low Voltage 0.8 V Input Current −1 +1 μA Per pin Pin Capacitance 2.6 pF Per pin

DIGITAL OUTPUTS2

SDO, ALERT

VOL, Output Low Voltage 0.4 V Sinking 200 μA VOH, Output High Voltage DVDD − 0.5 V Sourcing 200 μA High Impedance Leakage Current −1 +1 μA High Impedance Output

2.5 pF

Capacitance

FAULT

VOL, Output Low Voltage 0.4 V 10 kΩ pull-up resistor to DVDD VOL, Output Low Voltage 0.6 V At 2.5 mA VOH, Output High Voltage 3.6 V 10 kΩ pull-up resistor to DVDD

POWER REQUIREMENTS

AVDD 9 33 V DVDD 2.7 5.5 V AVCC 4.5 5.5 V AIDD 7 7.5 mA DICC 9.2 11 mA VIH = DVDD, VIL = DGND, internal oscillator running,

AICC 1 mA Over supplies

1 mA Per channel, current output mode, 0 mA output

BOOST

Power Dissipation 155 mW AVDD = 15 V, DVCC = 5 V, dc-to-dc converter enable,

Temperature range: −40°C to +105°C; typical at +25°C.

Guaranteed by design and characterization; not production tested.

For current outputs with internal R

loaded with the same code.

See the Current Output Mode with Internal R

Efficiency plots in Figure 33, Figure 34, Figure 35, and Figure 36 include the I

, the offset, full-scale, and TUE measurements exclude dc crosstalk. The measurements are made with all four channels enabled

SET

section for more explanation of the dc crosstalk.

SET

quiescent current.

BOOST

See Figure 42

See Figures 43 See Figure 42

converter switching frequency

over supplies

current output mode, outputs disabled

Rev. B | Page 6 of 44

Data Sheet AD5757

AC PERFORMANCE CHARACTERISTICS

AVDD = V REFIN = 5 V; R

Table 2.

Parameter1 Min Typ Max Unit Test Conditions/Comments

DYNAMIC PERFORMANCE

Current Output

Output Current Settling Time 15 μs To 0.1% FSR (0 mA to 24 mA)

Output Noise (0.1 Hz to 10 Hz

Bandwidth)

Output Noise Spectral Density 0.5 nA/√Hz

Guaranteed by design and characterization; not production tested.

TIMING CHARACTERISTICS

AVDD = V REFIN = 5 V; R

= 15 V; DVDD = 2.7 V to 5.5 V; AVCC = 4.5 V to 5.5 V; dc-to-dc converter disabled; AGND = DGND = GNDSWx = 0 V;

BOOST_x

= 300 Ω; all specifications T

MIN

to T

, unless otherwise noted.

MAX

See test conditions/

ms See Figure 26, Figure 27, and Figure 28

comments

0.15 LSB p-p 16-bit LSB, 0 mA to 24 mA range

Measured at 10 kHz, midscale output, 0 mA to 24 mA range

= 15 V; DVDD = 2.7 V to 5.5 V; AVCC = 4.5 V to 5.5 V; dc-to-dc converter disabled; AGND = DGND = GNDSWx = 0 V;

BOOST_x

= 300 Ω; all specifications T

MIN

to T

, unless otherwise noted.

MAX

Table 3.

Parameter

1, 2, 3

Limit at T

, T

Unit Description

MIN

MAX

t1 33 ns min SCLK cycle time t2 13 ns min SCLK high time t3 13 ns min SCLK low time t4 13 ns min

t5 13 ns min t6 198 ns min

falling edge to SCLK falling edge setup time

SYNC

/32nd SCLK falling edge to SYNC rising edge (see ) Figure 54

high time

SYNC t7 5 ns min Data setup time t8 5 ns min Data hold time t9 20 μs min

rising edge to LDAC falling edge (all DACs updated or any channel has

SYNC

digital slew rate control enabled) 5 μs min t10 10 ns min

t11 500 ns max t12

See the AC Performance

μs max DAC output settling time

rising edge to LDAC falling edge (single DAC updated)

SYNC

pulse width low

LDAC

falling edge to DAC output response time

LDAC

Characteristics section t13 10 ns min CLEAR high time t14 5 μs max CLEAR activation time t15 40 ns max SCLK rising edge to SDO valid t16 21 μs min

5 μs min t17 500 ns min t18 800 ns min

20 μs min

5 μs min

rising edge to DAC output response time (LDAC = 0) (all DACs updated)

SYNC

rising edge to DAC output response time (LDAC = 0) (single DAC updated)

SYNC

falling edge to SYNC rising edge

LDAC

pulse width

RESET

high to next SYNC low (digital slew rate control enabled) (all DACs updated)

SYNC

high to next SYNC low (digital slew rate control disabled) (single DAC

SYNC updated)

Guaranteed by design and characterization; not production tested.

All input signals are specified with t

See Figure 3, Figure 4, Figure 5, and Figure 6.

This specification applies if

LDAC

= t

= 5 ns (10% to 90% of DVDD) and timed from a voltage level of 1.2 V.

RISE

FALL

is held low during the write cycle; otherwise, see t9.

Rev. B | Page 7 of 44

AD5757 Data Sheet

Timing Diagrams

SCLK

SYNC

SDIN

LDAC

OUT_x

LDAC = 0

OUT_x

CLEAR

OUT_x

12 24

MSB

LSB

RESET

09225-002

Figure 3. Serial Interface Timing Diagram

SCLK

SYNC

SDIN

SDO

1 1

MSB MSBLSB LSB

INPUT WORD SPECIFIES REGISTER TO BE READ

UNDEFINED SELECTED REGISTER DATA

24 24

NOP CONDITI ON

MSB LSB

CLOCKED OUT

Figure 4. Readback Timing Diagram

09225-003

Rev. B | Page 8 of 44

Data Sheet AD5757

SCLK

SYNC

SDIN

SDO

LSB MSB

12 16

DUT_

R/W

DUT_

AD1

SDO DISABLED

XXXD15D14 D1D0

AD0

SDO_ ENAB

STATUSSTATUSSTATUSSTATUS

09225-004

Figure 5. Status Readback During Write

TO OUTPUT

50pF

200µA I

VOH (MIN) OR

(MAX)

09225-005

Figure 6. Load Circuit for SDO Timing Diagram

Rev. B | Page 9 of 44

AD5757 Data Sheet

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted. Transient currents of up to 100 mA do not cause SCR latch-up.

Table 4.

Parameter Rating

AVDD, V

to AGND, DGND −0.3 V to +33 V

BOOST_x

AVCC to AGND −0.3 V to +7 V DVDD to DGND −0.3 V to +7 V Digital Inputs to DGND

−0.3 V to DV

+ 0.3 V or +7 V

(whichever is less)

Digital Outputs to DGND

−0.3 V to DV

+ 0.3 V or +7 V

(whichever is less)

REFIN, REFOUT to AGND

−0.3 V to AV

+ 0.3 V or +7 V

(whichever is less)

OUT_x

to AGND

AGND to V

or 33 V if using

BOOST_x

the dc-to-dc circuitry SWx to AGND −0.3 V to +33 V AGND, GNDSWx to DGND −0.3 V to +0.3 V Operating Temperature Range ( TA)

Industrial1 −40°C to +105°C Storage Temperature Range −65°C to +150°C Junction Temperature (TJ max) 125°C 64-Lead LFCSP

θJA Thermal Impedance2 20°C/W Power Dissipation (TJ max – TA)/θJA Lead Temperature JEDEC industry standard

Soldering J-STD-020

Power dissipated on chip must be derated to keep the junction temperature

below 125°C.

Based on a JEDEC 4-layer test board.

Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

ESD CAUTION

Rev. B | Page 10 of 44

Data Sheet AD5757

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

DCDC_D

PIN 1

INDICATO R

SET_CRSET_D

REFOUT

REFINNCCHARTD

646362616059585756555453525150

BOOST_D

OUT_D

IGATED

COMP

AGNDNCCHARTCNCIGATEC

SET_B

SET_A

REFGND REFGND

NOTES

1. NC = NO CONNECT. DO NOT CONNECT TO T HIS PIN.

2. THE EXPOSED PAD SHOULD BE CONNECTED TO AGND, OR ALTERNATIVELY, IT CAN BE LE FT EL ECTRICALLY UNCONNECT ED. IT IS RECOMMENDED THAT THE PAD BE THE RMALLY CO NNECTED TO A COPPER PLANE FO R ENHANCED THERMAL PE RFORMANCE.

AD0

AD1 SYNC SCLK

SDIN

SDO

DGND

LDAC

CLEAR ALERT FAULT

3 4 5 6 7 8

9 10 11

12 13 14 15 16

171819202122232425262728293031

DGND

RESET

AD5757

TOP VIEW

(Not to Scale)

DCDC_A

IGATEA

BOOST_A

CHARTA

COMP

OUT_A

AGND

DCDC_B

IGATEB

CHARTB

COMP

48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33

COMP I

OUT_C

BOOST_C

GNDSW GNDSW

AGND SW

GNDSW GNDSW

AGND V

BOOST_B

OUT_B

DCDC_C

09225-006

Figure 7. Pin Configuration

Table 5. Pin Function Descriptions

Pin No. Mnemonic Description

1 R

SET_B

An external, precision, low drift 15 kΩ current setting resistor can be connected to this pin to improve the I temperature drift performance. See the Device Features section.

2 R

SET_A

An external, precision, low drift 15 kΩ current setting resistor can be connected to this pin to improve the I

temperature drift performance. See the Device Features section. 3, 4 REFGND Ground Reference Point for Internal Reference. 5 AD0 Address Decode for the Device Under Test (DUT) on the Board. 6 AD1 Address Decode for the DUT on the Board. 7

Active Low Input. This is the frame synchronization signal for the serial interface. While SYNC is low, data is

SYNC

transferred in on the falling edge of SCLK. 8 SCLK

Serial Clock Input. Data is clocked into the input shift register on the falling edge of SCLK. This pin operates at

clock speeds of up to 30 MHz. 9 SDIN Serial Data Input. Data must be valid on the falling edge of SCLK. 10 SDO Serial Data Output. Used to clock data from the serial register in readback mode. See Figure 4 and Figure 5. 11 DVDD Digital Supply. The voltage range is from 2.7 V to 5.5 V. 12, 17 DGND Digital Ground. 13

Load DAC, Active Low Input. This is used to update the DAC register and consequently the DAC outputs. When

LDAC

tied permanently low, the addressed DAC data register is updated on the rising edge of SYNC. If LDAC is held

high during the write cycle, the DAC input register is updated, but the DAC output update only takes place at

14 CLEAR

the falling edge of LDAC

LDAC

pin must not be left unconnected.

Active High, Edge Sensitive Input. Asserting this pin sets the output current and voltage to the preprogrammed

(see ). Using this mode, all analog outputs can be updated simultaneously. The Figure 3

clear code bit setting. Only channels enabled to be cleared are cleared. See the Device Features section for more

information. When CLEAR is active, the DAC output register cannot be written to.

OUT_B

OUT_A

Rev. B | Page 11 of 44

AD5757 Data Sheet

Pin No. Mnemonic Description

15 ALERT

FAU LT

RESET 19 AVDD Positive Analog Supply. The voltage range is from 10.8 V to 33 V. 20, 25,

NC No Connect. Do not connect to this pin. 28, 30, 50, 52, 55, 60

21 CHARTA HART Input Connection for DAC Channel A. 22 IGATEA

23 COMP

24 V

26 I

DCDC_A

BOOST_A

Current Output Pin for DAC Channel A.

OUT_A

27, 40, 53 AGND Ground Reference Point for Analog Circuitry. This must be connected to 0 V. 29 CHARTB HART Input Connection for DAC Channel B. 31 IGATEB

32 COMP

33 I 34 V

DCDC_B

Current Output Pin for DAC Channel B.

OUT_B

BOOST_B

35 AGND Ground Reference Point for Analog Circuitry. This pin must be connected to 0 V. 36 SWB

37 GNDSWB Ground Connection for DC-to-DC Switching Circuit. This pin should always be connected to ground. 38 GNDSWA Ground Connection for DC-to-DC Switching Circuit. This pin should always be connected to ground. 39 SWA

41 SWD

42 GNDSWD Ground Connections for DC-to-DC Switching Circuit. This pin should always be connected to ground. 43 GNDSWC Ground Connections for DC-to-DC Switching Circuit. This pin should always be connected to ground. 44 SWC

45 AVCC Supply for DC-to-DC Circuitry. 46 V

47 I 48 COMP

BOOST_C

Current Output Pin for DAC Channel C.

OUT_C

DCDC_C

49 IGATEC

Active High Output. This pin is asserted when there has been no SPI activity on the interface pins for a predetermined time. See the Device Features section for more information.

Active Low Output. This pin is asserted low when an open circuit in current mode is detected, a short circuit in voltage mode is detected, a PEC error is detected, or an overtemperature is detected (see the Device Features section). Open-drain output.

Hardware Reset. Active Low Input.

Optional Connection for External Pass Transistor. Should be left unconnected when using the dc-to-dc converter. See the External PMOS Mode section for more information.

DC-to-DC Compensation Capacitor. Connect a 10 nF capacitor from this pin to ground. Used to regulate the feedback loop of the Channel A dc-to-dc converter. Alternatively, if using an external compensation resistor, place a resistor in series with a capacitor to ground from this pin (see the DC-to-DC Converter Compensation Capacitors and the AICC Supply Requirements—Slewing sections in the Device Features section for more information).

Supply for Channel A Current Output Stage (see Figure 49). To use the dc-to-dc feature of the device, connect as shown in Figure 56.

Optional Connection for External Pass Transistor. Should be left unconnected when using the dc-to-dc converter. See the External PMOS Mode section for more information.

DC-to-DC Compensation Capacitor. Connect a 10 nF capacitor from this pin to ground. Used to regulate the feedback loop of the Channel B dc-to-dc converter. Alternatively, if using an external compensation resistor, place a resistor in series with a capacitor to ground from this pin (see the DC-to-DC Converter Compensation Capacitors and AI

Supply Requirements—Slewing sections in the Device Features section for more

information).

Supply for Channel B Current Output Stage (see Figure 49). To use the dc-to-dc feature of the device, connect as shown in Figure 56.

Switching Output for Channel B DC-to-DC Circuitry. To use the dc-to-dc feature of the device, connect as shown in Figure 56.

Switching Output for Channel A DC-to-DC Circuitry. To use the dc-to-dc feature of the device, connect as shown in Figure 56.

Switching Output for Channel D DC-to-DC Circuitry. To use the dc-to-dc feature of the device, connect as shown in Figure 56.

Switching Output for Channel C DC-to-DC Circuitry. To use the dc-to-dc feature of the device, connect as shown in Figure 56.

Supply for Channel C Current Output Stage (see Figure 49). To use the dc-to-dc feature of the device, connect as shown in Figure 56.

DC-to-DC Compensation Capacitor. Connect a 10 nF capacitor from this pin to ground. Used to regulate the feedback loop of the Channel C dc-to-dc converter. Alternatively, if using an external compensation resistor, place a resistor in series with a capacitor to ground from this pin (see the DC-to-DC Converter Compensation Capacitors and AICC Supply Requirements—Slewing sections in the Device Features section for more information).

Optional Connection for External Pass Transistor. Should be left unconnected when using the dc-to-dc converter. See the External PMOS Mode section for more information.

Rev. B | Page 12 of 44

Data Sheet AD5757

Pin No. Mnemonic Description

51 CHARTC HART Input Connection for DAC Channel C. 54 I 56 V

57 COMP

58 IGATED

59 CHARTD HART Input Connection for DAC Channel D. 61 REFIN External Reference Voltage Input. 62 REFOUT

63 R

64 R

EPAD

Current Output Pin for DAC Channel D.

OUT_D

BOOST_D

Supply for Channel D Current Output Stage (see Figure 49). To use the dc-to-dc feature of the device, connect as shown in Figure 56.

DCDC_D

DC-to-DC Compensation Capacitor. Connect a 10 nF capacitor from this pin to ground. Used to regulate the feedback loop of the Channel D dc-to-dc converter. Alternatively, if using an external compensation resistor, place a resistor in series with a capacitor to ground from this pin (see the DC-to-DC Converter Compensation Capacitors and AICC Supply Requirements—Slewing sections in the Device Features section for more information).

Optional Connection for External Pass Transistor. Should be left unconnected when using the dc-to-dc converter. See the External PMOS Mode section for more information.

Internal Reference Voltage Output. It is recommended to place a 0.1 μF capacitor between REFOUT and REFGND.

SET_D

An external, precision, low drift 15 kΩ current setting resistor can be connected to this pin to improve the I temperature drift performance. See the Device Features section.

SET_C

An external, precision, low drift 15 kΩ current setting resistor can be connected to this pin to improve the I temperature drift performance. See the Device Features section.

Exposed Pad. This exposed pad should be connected to AGND, or, alternatively, it can be left electrically unconnected. It is recommended that the pad be thermally connected to a copper plane for enhanced thermal performance.

OUT_D

OUT_C

Rev. B | Page 13 of 44

AD5757 Data Sheet

TYPICAL PERFORMANCE CHARACTERISTICS

CURRENT OUTPUTS

–0.0005

INL ERROR (%FSR)

–0.0010

–0.0015

–0.0020

–0.0025

0.0025

0.0020

0.0015

0.0010

0.0005

AVDD = 15V T

= 25°C

4mA TO 20mA, EXTERNAL R 4mA TO 20mA, EXTERNAL R 4mA TO 20mA, INTERNAL R 4mA TO 20mA, INTERNAL R 4mA TO 20mA, EXTERNAL R

0 10000 20000 30000 40000 50000 60000

SET

, WIT H DC-TO-DC CO NVERTER

SET

, WIT H DC-TO-DC CO NVERTER

SET

, EXTERNAL PM OS MODE

SET

CODE

Figure 8. Integral Nonlinearity vs. Code

09225-149

0.0010

0.0008

0.0006

0.0004

0.0002

–0.0002

INL ERROR (%FSR)

–0.0004

4mA TO 20mA RANGE MAX INL 0mA TO 24mA RANGE MAX INL 0mA TO 20mA RANGE MIN INL

0mA TO 20mA RANGE MAX INL 4mA TO 20mA RANGE MAX INL 0mA TO 24mA RANGE MIN INL

AVDD = 15V

–0.0006

–0.0008

–0.0010

–40 –20 0 20 40 60 80 100

TEMPERATURE (°C)

Figure 11. Integral Nonlinearity vs. Temperature, Internal R

09225-152

SET

1.0

4mA TO 20mA, EXTERNA L R 4mA TO 20mA, EXTERNA L R

0.8

4mA TO 20mA, INTERNAL R 4mA TO 20mA, INTERNAL R

0.6

4mA TO 20mA, EXTERNA L R

0.4

0.2

–0.2

DNL ERROR (LSB)

–0.4

–0.6

AVDD = 15V

–0.8

= 25°C

–1.0

0 10000 20000 30000 40000 50000 60000

SET

, WIT H DC-TO-DC CO NVERTER

SET

, WIT H DC-TO-DC CO NVERTER

SET

, EXTERNAL PM OS MODE

SET

CODE

Figure 9. Differential Nonlinearity vs. Code

0.035 AVDD = 15V

= 25°C

0.030

ALL CHANNELS ENABLED

0.025

–0.005

TOTAL UNADJUSTED ERROR (%FSR)

–0.010

–0.015

0.020

0.015

0.010

0.005

4mA TO 20mA, EXTERNAL R 4mA TO 20mA, EXTERNAL R 4mA TO 20mA, INTERNAL R 4mA TO 20mA, INTERNAL R 4mA TO 20mA, EXTERNAL R

0 10000 20000 30000 40000 50000 60000

SET

, WIT H DC-TO-DC CO NVERTER

SET

, WITH DC-TO-DC CO NVERTER

SET

, EXTERNAL PM OS MO DE

SET

CODE

Figure 10. Total Unadjusted Error vs. Code

0.0020

4mA TO 20mA RANGE MAX INL

0.0015

0.0010

0.0005

–0.0005

INL ERROR (%FSR)

–0.0010

–0.0015

–0.0020

–40 –20 0 20 40 60 80 100

09225-150

Figure 12. Integral Nonlinearity vs. Temperature, External R

1.0 AVDD = 15V

ALL RANGE S

0.8 INTERNAL AND EXTERNAL R

0.6

0mA TO 24mA RANGE MAX INL 0mA TO 20mA RANGE MI N INL

0mA TO 20mA RANGE MAX INL 4mA TO 20mA RANGE MI N INL 0mA TO 24mA RANGE MI N INL

AVDD = 15V

TEMPERATURE (°C)

SET

09225-153

SET

0.4

0.2

DNL ERROR M AX DNL ERROR M IN

–0.2

DNL ERROR (LSB)

–0.4

–0.6

–0.8

–1.0

–40 –20 0 20 40 60 80 100

09225-151

TEMPERATURE (°C)

09225-154

Figure 13. Differential Nonlinearity vs. Temperature

Rev. B | Page 14 of 44

Data Sheet AD5757

0.03

0.02

0.01

–0.01

–0.02

–0.03

–0.04

–0.05

–0.06

TOTAL UNADJSUTED ERROR (%FSR)

–0.07

–0.08

–40 –20 0 20 40 60 80 100

AVDD = 15V

4mA TO 20mA INTERNAL R 0mA TO 20mA INTERNAL R 0mA TO 24mA INTERNAL R 4mA TO 20mA EXTE RNAL R 0mA TO 20mA EXTE RNAL R 0mA TO 24mA EXTE RNAL R

TEMPERATURE (°C)

SET

Figure 14. Total Unadjusted Error vs. Temperature

0.03

0.02

0.01

–0.01

–0.02

–0.03

–0.04

–0.05

FULL-SCAL E ERROR (%FSR)

–0.06

–0.07

–0.08

–40 –20 0 20 40 60 80 100

AVDD = 15V

4mA TO 20mA INTERNAL R 0mA TO 20mA INTERNAL R 0mA TO 24mA INTERNAL R 4mA TO 20mA EXTE RNAL R 0mA TO 20mA EXTE RNAL R 0mA TO 24mA EXTE RNAL R

TEMPERATURE (°C)

SET

Figure 15. Full-Scale Error vs. Temperature

0.020

09225-155

09225-157

0.02

0.01

–0.01

–0.02

–0.03

GAIN ERRO R (%FSR)

–0.04

–0.05

–0.06

–40 –20 0 20 40 60 80 100

AVDD = 15V

4mA TO 20mA INT ERNAL R 0mA TO 20mA INT ERNAL R 0mA TO 24mA INT ERNAL R 4mA TO 20mA EXTERNAL R 0mA TO 20mA EXTERNAL R 0mA TO 24mA EXTERNAL R

TEMPERATURE (°C)

Figure 17. Gain Error vs. Temperature

0.0025

0.0020

0.0015

0.0010

0.0005

–0.0005

INL ERROR (%FSR)

–0.0010

–0.0015

–0.0020

4mA TO 20mA RANGE MAX INL 4mA TO 20mA RANGE MIN I NL T

= 25°C

10 15 20 25 30

SUPPLY (V)

Figure 18. Integral Nonlinearity Error vs. AV

Over Supply, External R

0.0015

SET

09225-159

09225-056

0.015

0.010

0.005

–0.005

OFFSET ERROR (%FSR)

–0.010

–0.015

–0.020

–40 –20 0 20 40 60 80 100

AVDD = 15V

4mA TO 20mA INTERNAL R 0mA TO 20mA INTERNAL R 0mA TO 24mA INTERNAL R 4mA TO 20mA EXTERNAL R 0mA TO 20mA EXTERNAL R 0mA TO 24mA EXTERNAL R

TEMPERATURE (°C)

Figure 16. Offset Error vs. Temperature

SET

09225-158

Rev. B | Page 15 of 44

0.0010

0.0005

–0.0005

–0.0010

INL ERROR (%FSR)

–0.0015

–0.0020

–0.0025

4mA TO 20mA RANGE MAX INL 4mA TO 20mA RANGE MIN I NL T

= 25°C

10 15 20 25 30

SUPPLY (V)

Figure 19. Integral Nonlinearity Error vs. AV

Over Supply, Internal R

09225-057

SET

AD5757 Data Sheet

1.0 ALL RANGES

INTERNAL AND EXT ERNAL R

0.8 TA = 25°C

0.6

0.4

0.2

DNL ERROR MAX

DNL ERROR MIN

–0.2

DNL ERROR (LSB)

–0.4

–0.6

–0.8

–1.0

10 15 20 25 30

SET

SUPPLY (V)

Figure 20. Differential Nonlinearity Error vs. AV

09225-162

0.006

0.004

0.002

–0.002

–0.004

–0.006

–0.008

TOTAL UNADJUST ED ERROR (%FS R)

–0.010

–0.012

10 15 20 25 30

MAX OF TUE

MIN OF TUE

BOOST_ X

Figure 23. Total Unadjusted Error vs. V

TA = 25°C EXTERNAL PMOS (NTL JS4149) 4mA TO 20mA RANGE R

= 300Ω

LOAD

SUPPLY (V)

, Using External PMOS Mode

BOOST_X

09225-188

0.012

0.010

0.008

0.006

0.004

4mA TO 20mA RANG E MAX TUE

TOTAL UNADJUSTED ERROR ( %FSR)

0.002

4mA TO 20mA RANG E MIN TUE

= 25°C

10 15 20 25 30

SUPPLY (V)

Figure 21. Total Unadjusted Error vs. AV

–0.002

–0.004

TOTAL UNADJUSTED ERRO R (%FSR)

–0.006

–0.008

–0.010

–0.012

–0.014

–0.016

–0.018

–0.020

4mA TO 20mA RANG E MAX TUE 4mA TO 20mA RANG E MIN TUE

= 25°C

10 15 20 25 30

SUPPLY (V)

Figure 22. Total Unadjusted Error vs. AV

, External R

, Internal R

CURRENT (µA)

09225-060

SET

09225-061

SET

0215105

TIME (µs)

Figure 24. Output Current vs. Time on Power-Up

–2

–4

VOLTAGE (µA)

–6

–8

–10

0123456

TIME (µs)

Figure 25. Output Current vs. Time on Output Enable

AVDD = 15V

= 25°C

= 300Ω

LOAD

AVDD = 15V

= 25°C

= 300Ω

LOAD

INT_ENABLE

09225-062

09225-063

Rev. B | Page 16 of 44

Data Sheet AD5757

OUTPUT CURRE NT (mA)

–0.50 –0.25 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

Figure 26. Output Current and V

0mA TO 24mA RANGE 1kΩ LOAD

= 410kHz

INDUCTOR = 10µH (XAL4040-103)

= 5V

= 25°C

TIME (ms)

BOOST_x

OUT

BOOST

Settling Time with DC-to-DC

09225-167

Converter (See Figure 56)

OUTPUT CURRENT (mA)

–0.25 0 0.25 0. 50 0.75 1.00 1.25 1. 50 1.75

, TA = –40°C

OUT

, TA = +25°C

OUT

, TA = +105°C

OUT

0mA TO 24mA RANGE 1kΩ LOAD

= 410kHz

INDUCTOR = 10µH (XAL 4040-103) AV

= 5V

TIME (ms)

09225-168

Figure 27. Output Current Settling with DC-to-DC Converter vs. Time and

Temperature (See Figure 56)

OUTPUT CURRENT (mA)

–0.25 0 0.25 0. 50 0.75 1.00 1.25 1. 50 1.75

, AVCC = 4.5V

OUT

, AVCC = 5.0V

OUT

, AVCC = 5.5V

OUT

0mA TO 24mA RANGE 1kΩ LOAD

= 410kHz

INDUCTOR = 10µH (XAL 4040-103) T

= 25°C

TIME (ms)

09225-169

Figure 28. Output Current Settling with DC-to-DC Converter vs. Time and

(See Figure 56)

(4mA TO 20mA STEP)

TOTAL UNADJUST ED ERROR (%FSR)

–5 501015

OUT

TA = 25°C EXTERNAL PMOS (NTLJS4149) 4mA TO 20mA RANGE R

= 300Ω

LOAD

= 24V

BOOST_X

(20mA TO 4mA STEP)

OUT

TIME (µs)

09225-189

Figure 29. Output Current Settling Time with External PMOS Transistor

Rev. B | Page 17 of 44

AD5757 Data Sheet

–2

–4

CURRENT (AC COUPLED) (µA)

–6

–8

–10

02468101214

20mA OUTPUT 10mA OUTPUT

AVCC = 5V

= 410kHz

INDUCTOR = 10µH (XAL4040-103)

TIME (µs)

0mA TO 2 4mA RANG E

1kΩ LOAD

EXTERNAL R

SET

TA = 25°C

09225-170

Figure 30. Output Current vs. Time with DC-to-DC Converter (See Figure 56)

AVDD = 15V V

= 15V

–20

–40

–60

PSRR (dB)

OUT_x

–80

–100

–120

BOOST

= 25°C

10 100 1k 10k 100k 1M 10M

Figure 32. I

FREQUENCY (Hz )

PSRR vs. Frequency

OUT_x

09225-068

HEADROOM VOL TAGE (V)

0 5 10 15 20

0mA TO 24mA RANGE 1kΩ LOAD

= 410kHz

INDUCTOR = 10µ H (XAL4040-103) T

= 25°C

CURRENT (mA)

09225-067

Figure 31. DC-to-DC Converter Headroom vs. Output Current (See Figure 56)

Rev. B | Page 18 of 44

Data Sheet AD5757

DC-TO-DC BLOCK

AVCC = 4.5V AV

= 5V

= 5.5V

20mA

EFFICIENCY (%)

BOOST_x

0220161284

Figure 33. Efficiency at V

EFFICIE NCY (%)

BOOST_ x

–40 10040 60 80200–20

20mA

0mA TO 24mA RANGE 1kΩ LOAD EXTERNAL R AVCC = 5V

= 410kHz

INDUCTOR = 10µ H (XAL4040-103)

Figure 34. Efficiency at V

0mA TO 24mA RANGE 1kΩ LOAD EXTERNAL R

INDUCTOR = 10µH (X AL4040-103) T

= 25°C

CURRENT (mA)

vs. Output Current (See Figure 56)

BOOST_x

SET

TEMPERATURE ( °C)

vs. Temperature (See Figure 56)

BOOST_x

= 410kHz

SET

EFFICIENCY (%)

OUT_x

09225-016

0mA TO 24mA RANGE 1kΩ LOAD EXTERNAL R AVCC = 5V

INDUCTOR = 10µH (XAL4040-103)

–40 10040 60 80200–20

SET

= 410 kHz

TEMPERAT URE (°C)

Figure 36. Output Efficiency vs. Temperature (See Figure 56)

0.6

0.5

0.4

0.3

0.2

SWITCH RESISTANCE (Ω)

0.1

0 –40 –20 0 20 40 60 80 100

09225-017

TEMPERATURE (°C)

Figure 37. Switch Resistance vs. Temperature

09225-019

09225-123

EFFICIENCY (%)

OUT_x

0220161284

AVCC = 4.5V

= 5V

= 5.5V

0mA TO 24mA RANGE 1kΩ LOAD EXTERNAL R

INDUCTOR = 10µH (X AL4040-103)

= 25°C

CURRENT (mA)

= 410kHz

SET

Figure 35. Output Efficiency vs. Output Current (See Figure 56)

09225-018

Rev. B | Page 19 of 44

AD5757 Data Sheet

REFERENCE

VOLTAGE (V)

–2

REF

OUT

TA = 25°C

0 0.2 0.4 0.6 0.8 1.0 1.2

TIME (ms)

Figure 38. REFOUT Turn-On Transient

AVDD = 15V T

= 25°C

09225-010

5.0050

5.0045

5.0040

5.0035

5.0030

5.0025

5.0020

REFOUT (V)

5.0015

5.0010

5.0005

5.0000 –40–20 0 20406080100

30 DEVICES SHOWN

= 15V

TEMPERAT URE (°C)

09225-163

Figure 41. REFOUT vs. Temperature (When the AD5757 is soldered onto a PCB, the reference shifts due to thermal shock on the package. The average output voltage shift is –4 mV. Measurement of these parts after seven days shows that the outputs typically shift back 2 mV toward their initial values.

This second shift is due to the relaxation of stress incurred during soldering.)

5.002

AVDD = 15V T

5.001

= 25°C

REFOUT (µV)

–1

–2

–3

0246 81

TIME (s)

Figure 39. REFOUT Output Noise (0.1 Hz to 10 Hz Bandwidth)

150

100

REFOUT (µV)

–50

–100

AVDD = 15V T

= 25°C

09225-011

5.000

4.999

4.998

REFOUT (V)

4.997

4.996

4.995 024681

LOAD CURRENT ( mA)

Figure 42. REFOUT vs. Load Current

5.00000

4.99995

4.99990

4.99985

4.99980

REFOUT (V)

4.99975

4.99970

4.99965

TA = 25°C

09225-014

–150

0 5 10 15 20

TIME (ms)

Figure 40. REFOUT Output Noise (100 kHz Bandwidth)

09225-012

4.99960 10 15 20 25 30

AVDD (V)

Figure 43. REFOUT vs. Supply

09225-015

Rev. B | Page 20 of 44

Data Sheet AD5757

GENERAL

450

400

350

300

250

(µA)

200

150

100

01234

Figure 44. DI

SDIN VOLTAGE (V)

vs. Logic Input Voltage

DVCC = 5V T

= 25°C

09225-007

13.4

13.3

13.2

13.1

13.0

12.9

FREQUENCY (MHz)

12.8

12.7

DVCC = 5.5V

12.6 –40 –20 0 20 40 60 80 100

TEMPERAT URE (°C)

Figure 46. Internal Oscillator Frequency vs. Temperature

09225-020

CURRENT (mA)

10 15 20 25 30

VOLTAGE (V)

Figure 45. AI

vs. AVDD

TA = 25°C I

= 0mA

OUT

09225-009

14.4

14.2

14.0

13.8

13.6

FREQUENCY ( MHz)

13.4

13.2 DVCC = 5.5V

= 25°C

13.0

Figure 47. Internal Oscillator Frequency vs. DV

2.5 3. 0 3.5 4. 0 4.5 5.0 5.5

VOLTAGE (V)

Supply Voltage

09225-021

Rev. B | Page 21 of 44

AD5757 Data Sheet

TERMINOLOGY

Relative Accuracy or Integral Nonlinearity (INL)

For the DAC, relative accuracy, or integral nonlinearity, is a measure of the maximum deviation, in LSBs, from the best fit line through the DAC transfer function. A typical INL vs. code plot is shown in Figure 8.

Differential Nonlinearity (DNL)

Differential nonlinearity (DNL) is the difference between the measured change and the ideal 1 LSB change between any two adjacent codes. A specified differential nonlinearity of ±1 LSB maximum ensures monotonicity. This DAC is guaranteed monotonic by design. A typical DNL vs. code plot is shown in Figure 9.

Monotonicity

A DAC is monotonic if the output either increases or remains constant for increasing digital input code. The AD5757 is monotonic over its full operating temperature range.

Offset Error

Offset error is the deviation of the analog output from the ideal zero-scale output when all DAC registers are loaded with 0x0000.

Gain Error

This is a measure of the span error of the DAC. It is the deviation in slope of the DAC transfer characteristic from the ideal, expressed in % FSR.

Gain TC

This is a measure of the change in gain error with changes in temperature. Gain TC is expressed in ppm FSR/°C.

Full-Scale Error

Full-Scale error is a measure of the output error when full-scale code is loaded to the DAC register. Ideally, the output should be full-scale − 1 LSB. Full-scale error is expressed in percent of full-scale range (% FSR).

Full-Scale TC

Full-scale TC is a measure of the change in full-scale error with changes in temperature and is expressed in ppm FSR/°C.

Tot a l U n ad ju s te d E rr o r

Total unadjusted error (TUE) is a measure of the output error taking all the various errors into account, including INL error, offset error, gain error, temperature, and time. TUE is expressed in % FSR.

DC Crosstalk

This is the dc change in the output level of one DAC in response to a change in the output of another DAC. It is measured with a full-scale output change on one DAC while monitoring another DAC, which is at midscale.

Current Loop Compliance Voltage

The maximum voltage at the I

pin for which the output

OUT_x

current is equal to the programmed value.

Voltage Reference Thermal Hysteresis

Voltage reference thermal hysteresis is the difference in output voltage measured at +25°C compared to the output voltage measured at +25°C after cycling the temperature from +25°C to

−40°C to +105°C and back to +25°C. The hysteresis is specified for the first and second temperature cycles and is expressed in ppm.

Power-On Glitch Energy

Power-on glitch energy is the impulse injected into the analog output when the AD5757 is powered-on. It is specified as the area of the glitch in nV-sec. See Figure 24.

Power Supply Rejection Ratio (PSRR)

PSRR indicates how the output of the DAC is affected by changes in the power supply voltage.

Reference TC

Reference TC is a measure of the change in the reference output voltage with a change in temperature. It is expressed in ppm/°C.

Line Regulation

Line regulation is the change in reference output voltage due to a specified change in supply voltage. It is expressed in ppm/V.

Load Regulation

Load regulation is the change in reference output voltage due to a specified change in load current. It is expressed in ppm/mA.

DC-to-DC Converter Headroom

This is the difference between the voltage required at the current output and the voltage supplied by the dc-to-dc converter. See Figure 31.

Output Efficiency

LOAD

OUT

AIAV

CCCC

This is defined as the power delivered to a channel’s load vs. the power delivered to the channel’s dc-to-dc input.

Efficiency at V

This is defined as the power delivered to a channel’s V

BOOST_x

AIAV

CCCC

xBOOSTOUT

BOOST_x

supply vs. the power delivered to the channel’s dc-to-dc input. The V

quiescent current is considered part of the dc-to-

BOOST_x

dc converter’s losses.

Rev. B | Page 22 of 44

Data Sheet AD5757

THEORY OF OPERATION

The AD5757 is a quad, precision digital-to-current loop converter designed to meet the requirements of industrial process control applications. It provides a high precision, fully integrated, low cost, single-chip solution for generating current loop outputs. The current ranges available are 0 mA to 20 mA, 0 mA to 24 mA, and 4 mA to 20 mA. The desired output configuration is user selectable via the DAC control register.

On-chip dynamic power control minimizes package power dissipation in current mode.

DAC ARCHITECTURE

The DAC core architecture of the AD5757 consists of two matched DAC sections. A simplified circuit diagram is shown in Figure 48. The four MSBs of the 16-bit data-word are decoded to drive 15 switches, E1 to E15. Each of these switches connects one of 15 matched resistors to either ground or the reference buffer output. The remaining 12 bits of the data-word drive Switch S0 to Switch S11 of a 12-bit voltage mode R-2R ladder network.

OUT

2R 2R

12-BIT R-2-R LADDER FOUR MSBs DECODED INTO

The voltage output from the DAC core is converted to a current (see Figure 49), which is then mirrored to the supply rail so that the application simply sees a current source output. The current outputs are supplied by V

Reference Buffers

The AD5757 can operate with either an external or internal reference. The reference input requires a 5 V reference for specified performance. This input voltage is then buffered before it is applied to the DAC.

2R 2R 2R 2R 2R

S0 S1 S11 E1 E2 E15

15 EQUAL SEGMENTS

Figure 48. DAC Ladder Structure

BOOST_x

BOOST _x

16-BIT

DAC

Figure 49. Voltage-to-Current Conversion Circuitry

SET

OUT_x

09225-069

09225-071

POWER-ON STATE OF THE AD5757

On power-up of the AD5757, the I

After device power-on or a device reset, it is recommended to wait 100 s or more before writing to the device to allow time for internal calibrations to take place.

pins are in tristate mode.

OUT_x

SERIAL INTERFACE

The AD5757 is controlled over a versatile 3-wire serial interface that operates at clock rates of up to 30 MHz and is compatible with SPI, QSPI, MICROWIRE, and DSP standards. Data coding is always straight binary.

Input Shift Register

The input shift register is 24 bits wide. Data is loaded into the device MSB first as a 24-bit word under the control of a serial clock input, SCLK. Data is clocked in on the falling edge of SCLK.

If packet error checking, or PEC (see the Device Features section), is enabled, an additional eight bits must be written to the AD5757, creating a 32-bit serial interface.

There are two ways in which the DAC outputs can be updated: individual updating or simultaneous updating of all DACs.

Individual DAC Updating

In this mode, the DAC data register. The addressed DAC output is updated on the rising edge of information.

Simultaneous Updating of All DACs

In this mode, into the DAC data register. Only the first write to each channel’s DAC data register is valid after quent writes while they are loaded into the DAC data register. All the DAC outputs are updated by taking

LDAC

is held low while data is being clocked into

SYNC

. See and for timing

Table 3 Figure 3

LDAC

is held high while data is being clocked

LDAC

is brought high. Any subse-

LDAC

is still held high are ignored, although

LDAC

low after

REFIN

LDAC

SCLK

SYNC

SDIN

Figure 50. Simplified Serial Interface of Input Loading Circuitry

16-BIT

DAC

DAC INPUT

DAC DATA

INTERFACE

LOGIC

for One DAC Channel

SYNC

OUTPUT

I/V AMPLIFIER

OFFSET

AND GAIN

CALIBRATIO N

SDO

is taken high.

OUT_x

09225-072

Rev. B | Page 23 of 44

AD5757 Data Sheet

TRANSFER FUNCTION

For the 0 mA to 20 mA, 0 mA to 24 mA, and 4 mA to 20 mA current output ranges, the output current is respectively expressed as

mA20

⎡

OUT

⎢ ⎣

⎡

OUT

⎢ ⎣

⎡

= DI

OUT

⎢ ⎣

where:

D is the decimal equivalent of the code loaded to the DAC. N is the bit resolution of the DAC.

⎤

⎥

⎦

mA24

⎤

⎥

⎦

mA16

⎤

+×

⎥ ⎦

mA4

Rev. B | Page 24 of 44

Data Sheet AD5757

REGISTERS

Tabl e 6 shows an overview of the registers for the AD5757.

Table 6. Data, Control, and Readback Registers for the AD5757

Data

DAC Data Register (×4)

Gain Register (×4)

Offset Register (×4)

Clear Code Register (×4)

Control

Main Control Register

Software Register

Slew Rate Control Register (×4)

DAC Control Register (×4) These registers are used to control the following:

DC-to-DC Control Register

Readback

Status Register This contains any fault information, as well as a user toggle bit.

Used to write a DAC code to each DAC channel. AD5757 data bits = D15 to D0. There are four DAC data registers, one per DAC channel.

Used to program gain trim, on a per channel basis. AD5757 data bits = D15 to D0. There are four gain registers, one per DAC channel.

Used to program offset trim, on a per channel basis. AD5757 data bits = D15 to D0. There are four offset registers, one per DAC channel.

Used to program clear code on a per channel basis. AD5757 data bits = D15 to D0. There are four clear code registers, one per DAC channel.

Used to configure the part for main operation. Sets functions such as status readback during write, enables output on all channels simultaneously, powers on all dc-to-dc converter blocks simultaneously, and enables and sets conditions of the watchdog timer. See the Device Features section for more details.

Has three functions. Used to perform a reset, to toggle the user bit and, as part of the watchdog timer feature, to verify correct data communication operation.

Used to program the slew rate of the output. There are four slew rate control registers, one per channel.

Set the output range, for example, 4 mA to 20 mA. Set whether an internal/external sense resistor is used. Enable/disable a channel for CLEAR. Enable/disable internal circuitry on a per channel basis. Enable/disable output on a per channel basis. Power on dc-to-dc converters on a per channel basis. There are four DAC control registers, one per DAC channel.

Use to set the dc-to-dc control parameters. Can control dc-to-dc maximum voltage, phase, and frequency.

Rev. B | Page 25 of 44

AD5757 Data Sheet

PROGRAMMING SEQUENCE TO WRITE/ENABLE THE OUTPUT CORRECTLY

To correctly write to and set up the part from a power-on condition, use the following sequence:

Perform a hardware or software reset after initial power-on.

The dc-to-dc converter supply block must be configured.

2. Set the dc-to-dc switching frequency, maximum output voltage allowed, and the phase that the four dc-to-dc channels clock at.

Configure the DAC control register on a per channel basis.

3. The output range is selected, and the dc-to-dc converter block is enabled (DC_DC bit). Other control bits can be configured at this point. Set the INT_ENABLE bit; however, the output enable bit (OUTEN) should not be set.

Write the required code to the DAC data register. This

4. implements a full DAC calibration internally. Allow at least 200 µs before Step 5 for reduced output glitch.

Write to the DAC control register again to enable the

5. output (set the OUTEN bit).

CHANGING AND REPROGRAMMING THE RANGE

When changing between ranges, the same sequence as described in the Programming Sequence to Write/Enable the Output Correctly section should be used. It is recommended to set the range to zero scale prior to disabling the output. Because the dc-to-dc switching frequency, maximum voltage, and phase have already been selected, there is no need to reprogram these. A flowchart of this sequence is shown in Figure 52.

CHANNEL’S O UTPUT I S ENABLED.

STEP 1: W RITE TO CHANNE L’S DAC DATA

STEP 2: W RITE TO DAC CO NTROL REG ISTER.

DISABLE THE OUTPUT (OUTEN = 0), AND SET THE NE W OUTP UT RANGE. KEEP THE DC_DC BIT AND THE INT_ENABL E BIT SE T.

STEP 3: WRITE VALUE TO THE DAC DATA REGISTER.

A flowchart of this sequence is shown in Figure 51.

POWER ON.

STEP 1: PERFORM A SO FTWARE /HARDWARE RESET.

STEP 2: W RITE TO DC-TO- DC CONTROL REGIST ER TO

SET DC-TO -DC CLOCK F REQUENCY, PHASE, AND MAXIMUM VOLTAGE.

STEP 3: WRITE TO DAC CONTROL REGISTER. SELECT THE DAC CHANNEL AND OUTPUT RANGE. SET T HE DC_DC BIT AND O THER CONT ROL BITS AS REQUIRED. SET THE INT_ENABLE BIT BUT DO NOT SELECT THE OUTEN BIT.

STEP 4: WRITE TO EACH/ALL DAC DATA REGI STERS. ALLOW AT LEAST 200µs BETWEEN STEP 3 AND STEP 5 FOR REDUCED O UTPUT GLITCH.

STEP 5: W RITE TO DAC CONTRO L REGISTER. REL OAD

SEQUENCE AS I N STEP 3 ABO VE. THI S TIME SELECT T HE OUTEN BI T TO ENABLE THE OUTPUT.

Figure 51. Programming Sequence for Enabling the Output Correctly

STEP 4: W RITE TO DAC CO NTROL REG ISTER.

RELOAD SEQUENCE AS IN ST EP 2 ABOVE. THIS TIME SELECT THE OUTEN BIT TO ENABLE THE OUTPUT.

09225-074

Figure 52. Steps for Changing the Output Range

09225-073

Rev. B | Page 26 of 44

Data Sheet AD5757

DATA REGISTERS

The input register is 24 bits wide. When PEC is enabled, the input register is 32 bits wide, with the last eight bits corresponding to the PEC code (see the Packet Error Checking section for more information on PEC). When writing to a data register, the format in Tabl e 7 must be used.

Table 7. Writing to a Data Register

MSB LSB D23 D22 D21 D20 D19 D18 D17 D16 D15 to D0

R/W

DUT_AD1 DUT_AD0 DREG2 DREG1 DREG0 DAC_AD1 DAC_AD0 Data

Table 8. Input Register Decode

Bit Description

R/W DUT_AD1, DUT_AD0

0 0 Addresses part with Pin AD1 = 0, Pin AD0 = 0 0 1 Addresses part with Pin AD1 = 0, Pin AD0 = 1 1 0 Addresses part with Pin AD1 = 1, Pin AD0 = 0 1 1 Addresses part with Pin AD1 = 1, Pin AD0 = 1 DREG2, DREG1, DREG0

DAC_AD1, DAC_AD0 These bits are used to decode the DAC channel.

0 0 DAC A 0 1 DAC B 1 0 DAC C 1 1 DAC D X X These are don’t cares if they are not relevant to the operation being performed.

Indicates a read from or a write to the addressed register. Used in association with the external pins, AD1 and AD0, to determine which AD5757 device is being addressed

by the system controller.

DUT_AD1 DUT_AD0 Function

Selects whether a data register or a control register is written to. If a control register is selected, a further decode of CREG bits (see Table 16) is required to select the particular control register, as follows.

DREG2 DREG1 DREG0 Function

0 0 0 Write to DAC data register (individual channel write) 0 1 0 Write to gain register 0 1 1 Write to gain register (all DACs) 1 0 0 Write to offset register 1 0 1 Write to offset register (all DACs) 1 1 0 Write to clear code register 1 1 1 Write to a control register

DAC_AD1 DAC_AD0 DAC Channel/Register Address

DAC Data Register

When writing to the AD5757 DAC data registers, D15 to D0 are used for the DAC data bits. Tabl e 9 shows the register format and Tabl e 8 describes the function of Bit D23 to Bit D16.

Table 9. Programming the DAC Data Registers

MSB LSB D23 D22 D21 D20 D19 D18 D17 D16 D15 to D0

R/W

DUT_AD1 DUT_AD0 DREG2 DREG1 DREG0 DAC_AD1 DAC_AD0 DAC data

Rev. B | Page 27 of 44

AD5757 Data Sheet

Gain Register

The 16-bit gain register, as shown in Ta ble 10 , allows the user to adjust the gain of each channel in steps of 1 LSB. This is done by setting the DREG[2:0] bits to 010. It is possible to write the same gain code to all four DAC channels at the same time by setting the DREG[2:0] bits to 011. The gain register coding is straight binary as shown in Tab l e 1 1 . The default code in the gain register is 0xFFFF. In theory, the gain can be tuned across the full range of the output. In practice, the maximum recommended gain trim is about 50% of programmed range to maintain accuracy. See the Digital Offset and Gain Control section for more information.

Table 10. Programming the Gain Register

R/W

0 Device address 0 1 0 DAC channel address Gain adjustment

DUT_AD1 DUT_AD0 DREG2 DREG1 DREG0 DAC_AD1 DAC_AD0 D15 to D0

Offset Register

The 16-bit offset register, as shown in Ta bl e 12 , allows the user to adjust the offset of each channel by −32,768 LSBs to +32,767 LSBs in steps of 1 LSB. This is done by setting the DREG[2:0] bits to

100. It is possible to write the same offset code to all four DAC channels at the same time by setting the DREG[2:0] bits to 101. The offset register coding is straight binary as shown in Tab l e 1 3 . The default code in the offset register is 0x8000, which results in zero offset programmed to the output. See the Digital Offset and Gain Control section for more information.

Clear Code Register

The 16-bit clear code register allows the user to set the clear value of each channel as shown in Tabl e 1 4 . It is possible, via software, to enable or disable on a per channel basis which channels are cleared when the CLEAR pin is activated. The default clear code is 0x0000. See the Asynchronous Clear section for more information.

Table 11. Gain Register

Gain Adjustment G15 G14 G13 G12 to G4 G3 G2 G1 G0

+65,535 LSBs 1 1 1 1 1 1 1 1 +65,534 LSBs 1 1 1 1 1 1 0 0 … … … … … … … … … 1 LSB 0 0 0 0 0 0 0 1 0 LSBs 0 0 0 0 0 0 0 0

Table 12. Programming the Offset Register

R/W

0 Device address 1 0 0 DAC channel address Offset adjustment

DUT_AD1 DUT_AD0 DREG2 DREG1 DREG0 DAC_AD1 DAC_AD0 D15 to D0

Table 13. Offset Register Options

Offset Adjustment OF15 OF14 OF13 OF12 to OF4 OF3 OF2 OF1 OF0

+32,767 LSBs 1 1 1 1 1 1 1 1 +32,766 LSBs 1 1 1 1 1 1 0 0 … … … … … … … … … No Adjustment (Default) 1 0 0 0 0 0 0 0 … … … … … … … … …

−32,767 LSBs 0 0 0 0 0 0 0 0

−32,768 LSBs 0 0 0 0 0 0 0 0

Table 14. Programming the Clear Code Register

R/W

0 Device address 1 1 0 DAC channel address Clear code

DUT_AD1 DUT_AD0 DREG2 DREG1 DREG0 DAC_AD1 DAC_AD0 D15 to D0

Rev. B | Page 28 of 44

Data Sheet AD5757

CONTROL REGISTERS

When writing to a control register, the format shown in Tab le 1 5 must be used. See Ta b l e 8 for information on the configuration of Bit D23 to Bit D16. The control registers are addressed by setting the DREG[2:0] bits to 111 and then setting the CREG[2:0] bits to the appropriate decode address for that register, according to Tabl e 1 6 . These CREG bits select among the various control registers.

Table 15. Writing to a Control Register

MSB LSB D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 to D0

R/W

DUT_AD1 DUT_AD0 1 1 1 DAC_AD1 DAC_AD0 CREG2 CREG1 CREG0 Data

Table 16. Register Access Decode

CREG2 (D15) CREG1 (D14) CREG0 (D13) Function

0 0 0 Slew rate control register (one per channel) 0 0 1 Main control register 0 1 0 DAC control register (one per channel) 0 1 1 DC-to-dc control register 1 0 0 Software register

Main Control Register

The main control register options are shown in Tab l e 1 7 and Tabl e 1 8 . See the Device Features section for more information on the features controlled by the main Control Register.

Table 17. Programming the Main Control Register

MSB LSB

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 to D0

0 0 1 0 STATREAD EWD WD1 WD0 X1 X1 OUTEN_ALL DCDC_ALL X1

X = don’t care.

Table 18. Main Control Register Functions

Bit Description

STATREAD Enable status readback during a write. See the Device Features section.

STATREAD = 1, enable. STATREAD = 0, disable (default).

EWD Enable watchdog timer. See the Device Features section for more information.

EWD = 1, enable watchdog. EWD = 0, disable watchdog (default).

WD1, WD0 Timeout select bits. Used to select the timeout period for the watchdog timer.

0 0 5 0 1 10 1 0 100 1 1 200 OUTEN_ALL Enables the output on all four DACs simultaneously.

DCDC_ALL When set, powers up the dc-to-dc converter on all four channels simultaneously.

WD1 WD0 Timeout Period (ms)

Do not use the OUTEN_ALL bit when using the OUTEN bit in the DAC control register.

To power down the dc-to-dc converters, all channel outputs must first be disabled. Do not use the DCDC_ALL bit when using the DC_DC bit in the DAC control register.

Rev. B | Page 29 of 44

AD5757 Data Sheet

DAC Control Register

The DAC control register is used to configure each DAC channel. The DAC control register options are shown in Tabl e 19 and Ta bl e 20 .

Table 19. Programming DAC Control Register

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

0 1 0 X1 X1 X1 X1 INT_ENABLE CLR_EN OUTEN RSET DC_DC X1 R2 R1 R0

X = don’t care.

Table 20. DAC Control Register Functions

Bit Description

INT_ENABLE

CLR_EN Per channel clear enable bit. Selects if this channel clears when the CLEAR pin is activated.

OUTEN Enables/disables the selected output channel.

RSET Selects an internal or external current sense resistor for the selected DAC channel.

DC_DC Powers the dc-to-dc converter on the selected channel.

R2, R1, R0 Selects the output range to be enabled.

1 0 0 4 mA to 20 mA current range 1 0 1 0 mA to 20 mA current range 1 1 0 0 mA to 24 mA current range

Powers up the dc-to-dc converter, DAC, and internal amplifiers for the selected channel. Does not enable the output. Can only be done on a per channel basis. It is recommended to set this bit and allow a >200 μs delay before enabling the output because this results in a reduced output enable glitch. Plots of this glitch can be found in Figure 25.

CLR_EN = 1, channel clears when the part is cleared. CLR_EN = 0, channel does not clear when the part is cleared (default).

OUTEN = 1, enables the channel. OUTEN = 0, disables the channel (default).

RSET = 0, selects the external resistor (default). RSET = 1, selects the internal resistor.

DC_DC = 1, power up the dc-to-dc converter. DC_DC = 0, power down the dc-to-dc converter (default). This allows per channel dc-to-dc converter power-up/power-down. To power down the dc-to-dc converter, the OUTEN and

INT_ENABLE bits must also be set to 0. All dc-to-dc converters can also be powered up simultaneously using the DCDC_ALL bit in the main control register.

R2 R1 R0 Output Range Selected

Rev. B | Page 30 of 44

Data Sheet AD5757

Software Register

The software register has three functions. It allows the user to perform a software reset to the part. It can be used to set the user toggle bit, D11, in the status register. It is also used as part of the watchdog feature when it is enabled. This feature is useful to ensure that communication has not been lost between the MCU and the AD5757 and that the datapath lines are working

SYNC

properly (that is, SDIN, SCLK, and

Table 21. Programming the Software Register

MSB LSB

D15 D14 D13 D12 D11 to D0

1 0 0 User program Reset code/SPI code

Table 22. Software Register Functions

Bit Description

User Program

This bit is mapped to Bit D11 of the status register. When this bit is set to 1, Bit D11 of the status register is set to 1. Likewise, when D12 is set to 0, Bit D11 of the status register is also set to zero. This feature can be used to ensure that the SPI pins are working correctly by writing a known bit value to this register and reading back the corresponding bit from the status register.

Reset Code/SPI Code

Option Description

Reset code Writing 0x555 to D[11:0] performs a reset of the AD5757. SPI code

If the watchdog timer feature is enabled, 0x195 must be written to the software register (D11 to D0) within the programmed timeout period.

When the watchdog feature is enabled, the user must write 0x195 to the software register within the timeout period. If this command is not received within the timeout period, the ALERT pin signals a fault condition. This is only required when the watchdog timer function is enabled.

DC-to-DC Control Register

The dc-to-dc control register allows the user control over the dc-to-dc switching frequency and phase, as well as the maximum allowable dc-to-dc output voltage. The dc-to-dc control register options are shown in Ta b le 2 3 and Tab l e 2 4 .

Table 23. Programming the DC-to-DC Control Register

MSB LSB

D15 D14 D13 D12 to D7 D6 D5 to D4 D3 to D2 D1 to D0

0 1 1 X1 DC-DC Comp DC-DC phase DC-DC Freq DC-DC MaxV

X = don’t care.

Table 24. DC-to-DC Control Register Options

Bit Description

DC-DC Comp

Selects between an internal and external compensation resistor for the dc-to-dc converter. See the DC-to-DC Converter Compensation Capacitors and AI

Supply Requirements—Slewing sections in the Device Features section for more

information. 0 = selects the internal 150 kΩ compensation resistor (default). 1 = bypasses the internal compensation resistor for the dc-to-dc converter. In this mode, an external dc-to-dc

compensation resistor must be used; this is placed at the COMP

pin in series with the 10 nF dc-to-dc compensation

DCDC_x

capacitor to ground. Typically, a ~50 kΩ resistor is recommended.

DC-DC Phase User programmable dc-to-dc converter phase (between channels).

00 = all dc-to-dc converters clock on the same edge (default). 01 = Channel A and Channel B clock on the same edge, Channel C and Channel D clock on opposite edges. 10 = Channel A and Channel C clock on the same edge, Channel B and Channel D clock on opposite edges. 11 = Channel A, Channel B, Channel C, and Channel D clock 90° out of phase from each other.

DC-DC Freq DC-to-dc switching frequency; these are divided down from the internal 13 MHz oscillator (see Figure 46 and Figure 47).

00 = 250 ± 10% kHz. 01 = 410 ± 10% kHz (default). 10 = 650 ± 10% kHz.

DC-DC MaxV Maximum allowed V

voltage supplied by the dc-to-dc converter.

BOOST_x

00 = 23 V + 1 V/−1.5 V (default). 01 = 24.5 V ± 1 V. 10 = 27 V ± 1 V. 11 = 29.5 V ± 1V.

Rev. B | Page 31 of 44

AD5757 Data Sheet

Slew Rate Control Register

This register is used to program the slew rate control for the selected DAC channel. The slew rate control is enabled/ disabled and programmed on a per channel basis. See Tab l e 2 5 and the Digital Slew Rate Control section for more information.

READBACK OPERATION

Readback mode is invoked by setting the R/W bit = 1 in the serial input register write. See for the bits associated with a readback operation. The DUT_AD1 and DUT_AD0 bits, in association with Bits RD[4:0], select the register to be read. The remaining data bits in the write sequence are don’t cares. During the next SPI transfer (see ), the data appearing on the SDO output contains the data from the previously addressed register. This second SPI transfer should either be a request to read yet another register on a third data transfer or a

Table 25. Programming the Slew Rate Control Register

D15 D14 D13 D12 D11 to D7 D6 to D3 D2 to D0

0 0 0 SREN X1 SR_CLOCK SR_STEP

X = don’t care.

Table 26. Input Shift Register Contents for a Read Operation

D23 D22 D21 D20 D19 D18 D17 D16 D15 to D0

R/W

X = don’t care.

DUT_AD1 DUT_AD0 RD4 RD3 RD2 RD1 RD0 X

Table 2 6

Figure 4

no operation command. The no operation command for DUT_AD[1:0] = 00 is 0x1CE000; for other DUT addresses, Bit D22 and Bit D21 are set accordingly.

Readback Example

To read back the gain register of Device 1, Channel A on the AD5757, implement the following sequence:

Write 0xA80000 to the AD5757 input register. This

configures the AD5757 Device Address 1 for read mode with the gain register of Channel A selected. All the data bits, D15 to D0, are don’t cares.

Follow with another read command or a no operation

2. command (0x3CE000). During this command, the data from the Channel A gain register is clocked out on the SDO line.

Table 27. Read Address Decoding

RD4 RD3 RD2 RD1 RD0 Function

0 0 0 0 0 Read DAC A data register 0 0 0 0 1 Read DAC B data register 0 0 0 1 0 Read DAC C data register 0 0 0 1 1 Read DAC D data register 0 0 1 0 0 Read DAC A control register 0 0 1 0 1 Read DAC B control register 0 0 1 1 0 Read DAC C control register 0 0 1 1 1 Read DAC D control register 0 1 0 0 0 Read DAC A gain register 0 1 0 0 1 Read DAC B gain register 0 1 0 1 0 Read DAC C gain register 0 1 0 1 1 Read DAC D gain register 0 1 1 0 0 Read DACA offset register 0 1 1 0 1 Read DAC B offset register 0 1 1 1 0 Read DAC C offset register 0 1 1 1 1 Read DAC D offset register 1 0 0 0 0 Clear DAC A code register 1 0 0 0 1 Clear DAC B code register 1 0 0 1 0 Clear DAC C code register 1 0 0 1 1 Clear DAC D code register 1 0 1 0 0 DAC A slew rate control register 1 0 1 0 1 DAC B slew rate control register 1 0 1 1 0 DAC C slew rate control register 1 0 1 1 1 DAC D slew rate control register 1 1 0 0 0 Read status register 1 1 0 0 1 Read main control register 1 1 0 1 0 Read dc-to-dc control register

Rev. B | Page 32 of 44

Data Sheet AD5757

Status Register

The status register is a read only register. This register contains any fault information as a well as a ramp active bit and a user toggle bit. When the STATREAD bit in the main control

Table 28. Decoding the Status Register

MSB LSB D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

DC-

DCD

DCC

X = don’t care.

DCB

DCA

User toggle

PEC error

Ramp active

Over TEMP

Table 29. Status Register Options

Bit Description

DC-DCD

This bit is set on Channel D if the dc-to-dc converter cannot maintain compliance (it may be reaching its V voltage). In this case, the I

fault bit is also set. See the DC-to-DC Converter V

OUT_D

information on this bit’s operation under this condition.

DC-DCC

This bit is set on Channel C if the dc-to-dc converter cannot maintain compliance (it may be reaching its V voltage). In this case, the I

fault bit is also set. See the DC-to-DC Converter V

OUT_C

information on this bit’s operation under this condition.

DC-DCB

This bit is set on Channel B if the dc-to-dc converter cannot maintain compliance (it may be reaching its V voltage). In this case, the I

fault bit is also set. See the DC-to-DC Converter V

OUT_B

information on this bit’s operation under this condition.

DC-DCA

This bit is set on Channel A if the dc-to-dc converter cannot maintain compliance (it may be reaching its V voltage). In this case, the I

fault bit is also set. See the DC-to-DC Converter V

OUT_A

information on this bit’s operation under this condition.

User toggle

User toggle bit. This bit is set or cleared via the software register. This can be used to verify data communications if

needed. PEC Error Denotes a PEC error on the last data-word received over the SPI interface. Ramp Active This bit is set while any one of the output channels is slewing (slew rate control is enabled on at least one channel). Over TEMP This bit is set if the AD5757 core temperature exceeds approximately 150°C. I

Fault This bit is set if a fault is detected on the I

OUT_D

Fault This bit is set if a fault is detected on the I

OUT_C

Fault This bit is set if a fault is detected on the I

OUT_B

Fault This bit is set if a fault is detected on the I

OUT_A

OUT_D

OUT_C

OUT_B

OUT_A

register is set, the status register contents can be read back on the SDO pin during every write sequence. Alternatively, if the STATREAD bit is not set, the status register can be read using the normal readback operation.

MAX

Functionality section for more

MAX

Functionality section for more

MAX

OUT_D

fault

OUT_C

fault

Functionality section for more

pin. pin. pin. pin.

OUT_B

fault

MAX

OUT_A

fault

Rev. B | Page 33 of 44

AD5757 Data Sheet

DEVICE FEATURES

OUTPUT FAULT

The AD5757 is equipped with a drain output allowing several AD5757 devices to be connected together to one pull-up resistor for global fault detection. The FAU LT

pin is forced active by any one of the following fault

scenarios:

• The voltage at I

OUT_x

range, due to an open-loop circuit or insufficient power supply voltage. The internal circuitry that develops the fault output avoids using a comparator with windowed limits because this requires an actual output error before

FAU LT

the

output becomes active. Instead, the signal is generated when the internal amplifier in the output stage has less than approximately 1 V of remaining drive capability. Thus, the the compliance limit is reached.

• An interface error is detected due to a PEC failure. See the

Packet Error Checking section.

• If the core temperature of the AD5757 exceeds

approximately 150°C.

The I

fault, PEC error, and over TEMP bits of the status

OUT_x

output to be activated.

FAU LT

pin, an active low open-

attempts to rise above the compliance

FAU LT

output activates slightly before

FAU LT

output to

DIGITAL OFFSET AND GAIN CONTROL

Each DAC channel has a gain (M) and offset (C) register, which allow trimming out of the gain and offset errors of the entire signal chain. Data from the DAC data register is operated on by a digital multiplier and adder controlled by the contents of the M and C registers. The calibrated DAC data is then stored in the DAC input register.

INPUT

Figure 53. Digital Offset and Gain control

Although Figure 53 indicates a multiplier and adder for each channel, there is only one multiplier and one adder in the device, and they are shared among all four channels. This has implications for the update speed when several channels are updated at once (see Tabl e 3).

Each time data is written to the M or C register, the output is not automatically updated. Instead, the next write to the DAC channel uses these M and C values to perform a new calibration and automatically updates the channel.

The output data from the calibration is routed to the DAC input register. This is then loaded to the DAC as described in the

DAC

REGISTE R

DAC

09225-075

Rev. B | Page 34 of 44

Theory of Operation section. Both the gain register and the offset register have 16 bits of resolution. The correct method to calibrate the gain/offset is to first calibrate out the gain and then calibrate the offset.

The value (in decimal) that is written to the DAC input register can be calculated by

DCode

rDACRegiste

×= C

−+

(1)

)1(

where:

D is the code loaded to the DAC channel’s input register. M is the code in the gain register (default code = 2 C is the code in the offset register (default code = 2

– 1).

STATUS READBACK DURING A WRITE

The AD5757 has the ability to read back the status register contents during every write sequence. This feature is enabled via the STATREAD bit in the main control register. This allows the user to continuously monitor the status register and act quickly in the case of a fault.

When status readback during a write is enabled, the contents of the 16-bit status register (see Tab l e 2 9 ) are output on the SDO pin, as shown in Figure 5.

The AD5757 powers up with this feature disabled. When this is enabled, the normal readback feature is not available, except for the status register. To read back any other register, clear the STATREAD bit first before following the readback sequence. STATREAD can be set high again after the register read.

ASYNCHRONOUS CLEAR

CLEAR is an active high, edge-sensitive input that allows the output to be cleared to a preprogrammed 16-bit code. This code is user programmable via a per channel 16-bit clear code register.

For a channel to clear, that channel must be enabled to be cleared via the CLR_EN bit in the channel’s DAC control register. If the channel is not enabled to be cleared, the output remains in its current state independent of the CLEAR pin level.

When the CLEAR signal is returned low, the relevant outputs remain cleared until a new value is programmed.

PACKET ERROR CHECKING

To verify that data has been received correctly in noisy environments, the AD5757 offers the option of packet error checking based on an 8-bit cyclic redundancy check (CRC-8). The device controlling the AD5757 should generate an 8-bit frame check sequence using the polynomial

C(x) = x

This is added to the end of the data-word, and 32 bits are sent to the AD5757 before taking 32-bit frame, it performs the error check when If the check is valid, the data is written to the selected register.

+ x2 + x1 + 1

SYNC

high. If the AD5757 sees a

SYNC

goes high.

Data Sheet AD5757

If the error check fails, the error bit in the status register is set. After reading the status

FAU LT

returns high (assuming there are no other

faults), and the PEC error bit is cleared automatically.

SYNC

FAU LT

pin goes low and the PEC

UPDATE ON SYNC H IGH

INTERNAL REFERENCE

The AD5757 contains an integrated 5 V voltage reference with initial accuracy of ±5 mV maximum and a temperature drift coefficient of ±10 ppm maximum. The reference voltage is buffered and externally available for use elsewhere within the system.

SCLK

SDIN

SYNC

SCLK

SDIN

FAULT

MSB

D23

24-BIT DATA

24-BIT DATA TRANSFER—NO ERROR CHECKING

MSB

D31

24-BIT DATA 8-BIT CRC

32-BIT DATA TRANSFER WI TH ERROR CHE CKING

Figure 54. PEC Timing

LSB

UPDATE ON SYNC HIGH

ONLY IF ERROR CHECK PASSED

LSB

D7 D0

FAULT PIN GOES LOW

IF ERROR CHECK FAILS

The PEC can be used for both transmit and receive of data packets. If status readback during a write is enabled, the PEC values returned during the status readback during a write operation should be ignored. If status readback during a write is disabled, the user can still use the normal readback operation to monitor status register activity with PEC.

WATCHDOG TIMER

When enabled, an on-chip watchdog timer generates an alert signal if 0x195 has not been written to the software register within the programmed timeout period. This feature is useful to ensure that communication has not been lost between the MCU and the AD5757 and that these datapath lines are working

SYNC

properly (that is, SDIN, SCLK, and

). If 0x195 is not received by the software register within the timeout period, the ALERT pin signals a fault condition. The ALERT signal is active high and can be connected directly to the CLEAR pin to enable a CLEAR in the event that communication from the MCU is lost.

The watchdog timer is enabled, and the timeout period (5 ms, 10 ms, 100 ms, or 200 ms) is set in the main control register (see Tabl e 1 7 and Tabl e 18).

OUTPUT ALERT

The AD5757 is equipped with an ALERT pin. This is an active high CMOS output. The AD5757 also has an internal watchdog timer. When enabled, it monitors SPI communications. If 0x195 is not received by the software register within the timeout period, the ALERT pin goes active.

EXTERNAL CURRENT SETTING RESISTOR

Referring to Figure 49, R of the voltage to current conversion circuitry. The stability of the output current value over temperature is dependent on the stability of the value of R stability of the output current over temperature, an external 15 kΩ low drift resistor can be connected to the R the AD5757 to be used instead of the internal resistor, R1. The external resistor is selected via the DAC control register (see Tabl e 1 9 ).

Tabl e 1 outlines the performance specifications of the AD5757 with both the internal R resistor. Using an external R performance over the internal R

resistor specification assumes an ideal resistor; the actual

SET

09225-008

performance depends on the absolute value and temperature coefficient of the resistor used. This directly affects the gain error of the output, and thus the total unadjusted error. To arrive at the gain/TUE error of the output with a particular external R resistor, add the percentage absolute error of the R directly to the gain/TUE error of the AD5757 with the external

resistor, shown in Tabl e 1 (expressed in % FSR).

SET

is an internal sense resistor as part

SET

. As a method of improving the

SET

SET_x

resistor and an external, 15 kΩ R

SET

resistor allows for improved

SET

resistor option. The external

SET

pin of

SET

resistor

SET

HART

The AD5757 has four CHART pins, one corresponding to each output channels. A HART signal can be coupled into these pins. The HART signal appears on the corresponding current output, if the output is enabled. Tab le 3 0 shows the recommended input voltages for the HART signal at the CHART pin. If these voltages are used, the current output should meet the HART amplitude specifications. Figure 55 shows the recommended circuit for attenuating and coupling in the HART signal.

Table 30. CHART Input Voltage to HART Output Current

CHART Input

SET

Internal R External R

Voltage

150 mV p-p 1 mA p-p

SET

170 mV p-p 1 mA p-p

SET

HART MODEM

OUTPUT

Figure 55. Coupling HART Signal

A minimum capacitance of C1 + C2 is required to ensure that the 1.2 kHz and 2.2 kHz HART frequencies are not significantly attenuated at the output. The recommended values are C1 = 22 nF, C2 = 47 nF.

Current Output (HART)

CHARTx

09225-076

Rev. B | Page 35 of 44

AD5757 Data Sheet

Digitally controlling the slew rate of the output is necessary to meet the analog rate of change requirements for HART.

DIGITAL SLEW RATE CONTROL

The slew rate control feature of the AD5757 allows the user to control the rate at which the output value changes. With the slew rate control feature disabled, the output value changes at a rate limited by the output drive circuitry and the attached load. To reduce the slew rate, this can be achieved by enabling the slew rate control feature. With the feature enabled via the SREN bit of the slew rate control register (see Ta b le 2 5), the output, instead of slewing directly between two values, steps digitally at a rate defined by two parameters accessible via the slew rate control register, as shown in Tab l e 2 5 . The parameters are SR_CLOCK and SR_STEP. SR_CLOCK defines the rate at which the digital slew is updated, for example, if the selected update rate is 8 kHz, the output updates every 125 µs. In conjunction with this, SR_STEP defines by how much the output value changes at each update. Together, both parameters define the rate of change of the output value. Ta bl e 31 and Tabl e 32 outline the range of values for both the SR_CLOCK and SR_STEP parameters.

Table 31. Slew Rate Update Clock Options

SR_CLOCK Update Clock Frequency (Hz)1

0000 64 k 0001 32 k 0010 16 k 0011 8 k 0100 4 k 0101 2 k 0110 1 k 0111 500 1000 250 1001 125 1010 64 1011 32 1100 16 1101 8 1110 4 1111 0.5

These clock frequencies are divided down from the 13 MHz internal

oscillator. See Table 1, Figure 46, and Figure 47.

Table 32. Slew Rate Step Size Options

SR_STEP Step Size (LSBs)

000 1 001 2 010 4 011 16 100 32 101 64 110 128 111 256

The following equation describes the slew rate as a function of the step size, the update clock frequency, and the LSB size:

TimeSlew

ChangeOutput

××

SizeLSBFrequencyClockUpdateSizeStep

where:

Slew Time is expressed in seconds. Output Change is expressed in amps for I

OUT_x

When the slew rate control feature is enabled, all output changes occur at the programmed slew rate (see the DC-to-DC Converter Settling Time section for additional information). For example, if the CLEAR pin is asserted, the output slews to the clear value at the programmed slew rate (assuming that the clear channel is enabled to be cleared). If a number of channels are enabled for slew, care must be taken when asserting the CLEAR pin. If one of the channels is slewing when CLEAR is asserted, other channels may change directly to their clear values not under slew rate control. The update clock frequency for any given value is the same for all output ranges. The step size, however, varies across output ranges for a given value of step size because the LSB size is different for each output range.

POWER DISSIPATION CONTROL

The AD5757 contains integrated dynamic power control using a dc-to-dc boost converter circuit, allowing reductions in power consumption from standard designs.

In standard current input module designs, the load resistor values can range from typically 50 Ω to 750 Ω. Output module systems must source enough voltage to meet the compliance voltage requirement across the full range of load resistor values. For example, in a 4 mA to 20 mA loop when driving 20 mA, a compliance voltage of >15 V is required. When driving 20 mA into a 50 Ω load, only 1 V compliance is required.

The AD5757 circuitry senses the output voltage and regulates this voltage to meet compliance requirements plus a small headroom voltage. The AD5757 is capable of driving up to 24 mA through a 1 kΩ load.

DC-TO-DC CONVERTERS

The AD5757 contains four independent dc-to-dc converters. These are used to provide dynamic control of the V voltage for each channel (see Figure 49). Figure 56 shows the discreet components needed for the dc-to-dc circuitry, and the following sections describe component selection and operation of this circuitry.

≥10µF

DCDC

10µH

SWx

Figure 56. DC-to-DC Circuit

DCDC

4.7µF

FILTER

10Ω

FILTER

0.1µF

BOOST

BOOST_X

supply

09225-077

Rev. B | Page 36 of 44

Data Sheet AD5757

Table 33. Recommended DC-to-DC Components

Symbol Component Value Manufacturer

XAL4040-103 10 μH Coilcraft®

DCDC

GRM32ER71H475KA88L 4.7 μF Murata

DCDC

PMEG3010BEA 0.38 VF NXP

DCDC

It is recommended to place a 10 Ω, 100 nF low-pass RC filter after C reduces the amount of ripple on the V

. This consumes a small amount of power but

DCDC

supply.

BOOST_x

DC-to-DC Converter Operation

The on-board dc-to-dc converters use a constant frequency, peak current mode control scheme to step up an AV

input of

4.5 V to 5.5 V to drive the AD5757 output channel. These are designed to operate in discontinuous conduction mode (DCM) with a duty cycle of <90% typical. Discontinuous conduction mode refers to a mode of operation where the inductor current goes to zero for an appreciable percentage of the switching cycle. The dc-to-dc converters are nonsynchronous; that is, they require an external Schottky diode.

DC-to-DC Converter Output Voltage

When a channel current output is enabled, the converter regulates the V

supply to 7.4 V (±5%) or (I

BOOST_x

OUT

× R

LOAD

+ Headroom), whichever is greater (see Figure 31 for a plot of headroom supplied vs. output current). When the output is disabled, the converter regulates the V

supply to 7.4 V (±5%).

BOOST_x

DC-to-DC Converter Settling Time

The settling time for a step greater than ~1 V (I

OUT

× R

LOAD

) is dominated by the settling time of the dc-to-dc converter. The exception to this is when the required voltage at the I

OUT_x

pin plus the compliance voltage is below 7.4 V (±5%). A typical plot of the output settling time can be found in Figure 26. This plot is for a 1 kΩ load. The settling time for smaller loads is faster. The settling time for current steps less than 24 mA is also faster.

DC-to-DC Converter V

The maximum V

BOOST_x

Functionality

MAX

voltage is set in the dc-to-dc control register (23 V, 24.5 V, 27 V, or 29.5 V; see Tab l e 2 4 ). On reaching this maximum voltage, the dc-to-dc converter is disabled, and the V V

BOOST_x

is reenabled, and the voltage ramps up again to V

voltage is allowed to decay by ~0.4 V. After the

BOOST_x

voltage has decayed by ~0.4 V, the dc-to-dc converter

, if still

MAX

required. This operation is shown in Figure 57.

29.6 V

MAX

DC_DC BIT

29.5

29.4

29.3

29.2

29.1

VOLTAGE (mV)

BOOST

DC-DCx BIT = 1

29.0

28.9

28.8

28.7

DC-DCx BIT = 0

28.6

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Figure 57. Operation on Reaching V

0mA TO 24mA RANGE, 24mA OUTPUT OUTPUT UNLOADED

DC-DCMaxV = 29.5V

= 410kHz

= 25°C

TIME (ms)

MAX

As shown in Figure 57, the DC-DCx bit in the status register asserts when the AD5757 is ramping to the V deasserts when the voltage is decaying to V

MAX

− ~0.4 V.

MAX

value but

DC-to-DC Converter On-Board Switch

The AD5757 contains a 0.425 Ω internal switch. The switch current is monitored on a pulse by pulse basis and is limited to

0.8 A peak current.

DC-to-DC Converter Switching Frequency and Phase

The AD5757 dc-to-dc converter switching frequency can be selected from the dc-to-dc control register. The phasing of the channels can also be adjusted so that the dc-to-dc converter can clock on different edges (see Tabl e 2 4 ). For typical applications, a 410 kHz frequency is recommended. At light loads (low output current and small load resistor), the dc-to-dc converter enters a pulse-skipping mode to minimize switching power dissipation.

DC-to-DC Converter Inductor Selection

For typical 4 mA to 20 mA applications, a 10 µH inductor (such as the XAL4040-103 from Coilcraft), combined with a switching frequency of 410 kHz, allows up to 24 mA to be driven into a load resistance of up to 1 kΩ with an AV

supply of 4.5 V to

5.5 V. It is important to ensure that the inductor is able to handle the peak current without saturating, especially at the maximum ambient temperature. If the inductor enters into saturation mode, it results in a decrease in efficiency. The inductance value also drops during saturation and may result in the dc-to-dc converter circuit not being able to supply the required output power.

DC-to-DC Converter External Schottky Selection

The AD5757 requires an external Schottky for correct operation. Ensure that the Schottky is rated to handle the maximum reverse breakdown expected in operation and that the rectifier maximum junction temperature is not exceeded. The diode average current is approximately equal to the I

LOAD

current. Diodes with larger forward voltage drops result in a decrease in efficiency.

09225-183

Rev. B | Page 37 of 44

AD5757 Data Sheet

DC-to-DC Converter Compensation Capacitors

As the dc-to-dc converter operates in DCM, the uncompensated transfer function is essentially a single-pole transfer function. The pole frequency of the transfer function is determined by the dc-to-dc converter’s output capacitance, input and output voltage, and output load. The AD5757 uses an external capacitor in conjunction with an internal 150 kΩ resistor to compensate the regulator loop. Alternatively, an external compensation resistor can be used in series with the compensation capacitor by setting the DC-DC Comp bit in the dc-to-dc control register. In this case, a ~50 kΩ resistor is recommended. A description of the advantages of this can be found in the AI

Supply

Requirements—Slewing section. For typical applications, a 10 nF dc-to-dc compensation capacitor is recommended.

DC-to-DC Converter Input and Output Capacitor Selection

The output capacitor affects ripple voltage of the dc-to-dc converter and indirectly limits the maximum slew rate at which the channel output current can rise. The ripple voltage is caused by a combination of the capacitance and equivalent series resistance (ESR) of the capacitor. For the AD5757, a ceramic capacitor of 4.7 µF is recommended for typical applications. Larger capacitors or paralleled capacitors improve the ripple at the expense of reduced slew rate. Larger capacitors also impact the AV AI

supplies current requirements while slewing (see the

Supply Requirements—Slewing section). This capacitance

at the output of the dc-to-dc converter should be >3 µF under all operating conditions.

The input capacitor provides much of the dynamic current required for the dc-to-dc converter and should be a low ESR component. For the AD5757, a low ESR tantalum or ceramic capacitor of 10 µF is recommended for typical applications. Ceramic capacitors must be chosen carefully because they can exhibit a large sensitivity to dc bias voltages and temperature. X5R or X7R dielectrics are preferred because these capacitors remain stable over wider operating voltage and temperature ranges. Care must be taken if selecting a tantalum capacitor to ensure a low ESR value.

AICC SUPPLY REQUIREMENTS—STATIC

The dc-to-dc converter is designed to supply a V

= I

× R

BOOST

OUT

+ Headroom (2)

LOAD

See Figure 31 for a plot of headroom supplied vs. output voltage. This means that, for a fixed load and output voltage, the dc-to-dc converter output current can be calculated by the following formula:

OutPower

AVEfficiency

BOOSTOUT

BOOST

where:

is the output current from I

OUT

is the efficiency at V

BOOST

BOOST_x

in amps.

OUT_x

as a fraction (see Figure 33

and Figure 34).

voltage of

BOOST_x

(3)

Rev. B | Page 38 of 44

AICC SUPPLY REQUIREMENTS—SLEWING

The AICC current requirement while slewing is greater than in static operation because the output power increases to charge the output capacitance of the dc-to-dc converter. This transient current can be quite large (see Figure 58), although the methods described in the Reducing AI can reduce the requirements on the AV

current can be provided, the AVCC voltage drops. Due to

this AV

drop, the AICC current required to slew increases

further. This means that the voltage at AV Equation 3) and the V

BOOST_x

age, may never reach its intended value. Because this AV voltage is common to all channels, this may also affect other channels.

0.8

0.7

0.6

0.5

0.4

CURRENT (A)

0.3

0.2

0.1

0 0.5 1.0 1.5 2.0 2.5

Figure 58. AI

OUT

BOOST

Current vs. Time for 24 mA Step Through 1 kΩ Load

with Internal Compensation Resistor

Reducing AICC Current Requirements

There are two main methods that can be used to reduce the AI

current requirements. One method is to add an external

compensation resistor, and the other is to use slew rate control. Both of these methods can be used in conjunction.

A compensation resistor can be placed at the COMP in series with the 10 nF compensation capacitor. A 51 kΩ external compensation resistor is recommended. This compensation increases the slew time of the current output but eases the AI transient current requirements. Figure 59 shows a plot of AI current for a 24 mA step through a 1 kΩ load when using a 51 kΩ compensation resistor. This method eases the current requirements through smaller loads even further, as shown in Figure 60.

Current Requirements section

supply. If not enough

drops further (see

voltage, and thus the output volt-

0mA TO 24mA RANGE

INDUCTOR = 10µ H (XAL4040-103)

TIME (ms)

1kΩ LOAD

= 410kHz

= 25°C

DCDC_x

VOLTAGE (V)

CURRENT (mA) / V

BOOST_x

OUT_x

09225-184

Data Sheet AD5757

0.8 0mA TO 24mA RANGE

1kΩ LOAD

= 410kHz

0.7

INDUCTOR = 10µ H (XAL4040-103)

= 25°C

0.6

0.5

0.4

CURRENT (A)

0.3

0.2

0.1

0 0.5 1.0 1.5 2.0 2.5

Figure 59. AI

Current vs. Time for 24 mA Step Through 1 kΩ Load

OUT

BOOST

TIME (ms)

VOLTAGE (V)

BOOST_x

CURRENT (mA) / V

OUT_x

with External 51 kΩ Compensation Resistor

0.8

0.7

0.6

0.5

0.4

CURRENT (A)

0.3

0.2

0.1

0 0.5 1.0 1.5 2.0 2.5

Figure 60. AI

OUT

BOOST

Current vs. Time for 24 mA Step Through 500 Ω Load

INDUCTOR = 10µH (XAL4040- 103)

TIME (ms)

0mA TO 24mA RANGE

500Ω LOAD

= 410kHz

= 25°C

VO LTAG E (V )

BOOST_x

CURRENT (mA )/ V

OUT_x

with External 51 kΩ Compensation Resistor

Using slew rate control can greatly reduce the AV

supplies cur-

rent requirements, as shown in Figure 61. When using slew rate control, attention should be paid to the fact that the output cannot slew faster than the dc-to-dc converter. The dc-to-dc converter slews slowest at higher currents through large (for example, 1 kΩ) loads. This slew rate is also dependent on the configuration of the dc-to-dc converter. Two examples of the dc-to-dc converter’s output slew are shown in Figure 59 and Figure 60 (V

BOOST

corre-

sponds to the dc-to-dc converter’s output voltage).

5.0V

(LEFT FLOATING)

09225-185

09225-186

BOOST_A

0.8 0mA TO 24mA RANGE

1kΩ LOAD

0.7

= 410kHz

INDUCTOR = 10µ H (XAL4040-103) T

= 25°C

0.6

0.5

0.4

CURRENT (A)

0.3

0.2

0.1

OUT

BOOST

01 2345 6

TIME (ms)

VOLTAGE (V)

BOOST_x

CURRENT (mA) / V

OUT_x

Figure 61. AICC Current vs. Time for 24 mA Step Through 1 kΩ Load

with Slew Rate Control

EXTERNAL PMOS MODE

The AD5757 can also be used with an external PMOS transistor per channel, as shown in Figure 62. This mode can be used to limit the on-chip power dissipation of the AD5757, though this will not reduce the power dissipation of the total system. The IGATE functionality is not typically required when using the dynamic power control feature so Figure 62 shows the configuration of the device for a fixed V

In this configuration the SW GNDSW

pin is grounded. The V

minimum supply of 7.5 V and a maximum supply of 33 V. This supply can be sized according to the maximum load required to be driven.

The IGATE functionality works by holding the gate of the external PMOS transistor at (V the majority of the channels power dissipation will take place in this external PMOS transistor.

The external PMOS transistor should be chosen tolerate a V voltage of at least −V

, as well as to handle the power

BOOST_x

dissipation required. This external PMOS transistor typically has minimal effect on the current output performance.

supply.

BOOST_x

pin are left floating and the

pin is connected to a

BOOST_x

− 5 V). This means that

BOOST_x

09225-187

R2 R3

DAC A

DAC CHANNEL A

SWGND

BOOST_ A

–5V)

OUT_A

IGATEA

SET_A

CHARTA

CURRENT OUTPUT

LOAD

09225-190

Figure 62. Configuration off a Particular Channel Using IGATE

Rev. B | Page 39 of 44

AD5757 Data Sheet

APPLICATIONS INFORMATION

CURRENT OUTPUT MODE WITH INTERNAL R

When using the internal R

resistor in current output mode,

SET

the output is significantly affected by how many other channels using the internal R these channels. The internal R for all channels enabled with the internal R

are enabled and by the dc crosstalk from

SET

specifications in Ta b le 1 are

SET

selected and

SET

outputting the same code.

For every channel enabled with the internal R

, the offset error

SET

decreases. For example, with one current output enabled using the internal R

, the offset error is 0.075% FSR. This value

SET

decreases proportionally as more current channels are enabled; the offset error is 0.056% FSR on each of two channels, 0.029% on each of three channels, and 0.01% on each of four channels.

Similarly, the dc crosstalk when using the internal R

is propor-

SET

tional to the number of current output channels enabled with the internal R

. For example, with the measured channel at

SET

0x8000 and one channel going from zero to full scale, the dc crosstalk is −0.011% FSR. With two channels going from zero to full scale, it is −0.019% FSR, and with all three other channels going from zero to full scale, it is −0.025% FSR.

For the full-scale error measurement in Tab le 1 , all channels are at 0xFFFF. This means that, as any channel goes to zero scale, the full-scale error increases due to the dc crosstalk. For example, with the measured channel at 0xFFFF and three channels at zero scale, the full-scale error is 0.025%. Similarly, if only one channel is enabled in current output mode with the internal

, the full-scale error is 0.025% FSR + 0.075% FSR = 0.1% FSR.

SET

PRECISION VOLTAGE REFERENCE SELECTION

To achieve the optimum performance from the AD5757 over its full operating temperature range, a precision voltage reference must be used. Thought should be given to the selection of a precision voltage reference. The voltage applied to the reference inputs is used to provide a buffered reference for the DAC cores. Therefore, any error in the voltage reference is reflected in the outputs of the device.

There are four possible sources of error to consider when choosing a voltage reference for high accuracy applications: initial accuracy, temperature coefficient of the output voltage, longterm drift, and output voltage noise.

Initial accuracy error on the output voltage of an external reference can lead to a full-scale error in the DAC. Therefore, to minimize these errors, a reference with low initial accuracy error specification is preferred. Choosing a reference with an output trim adjustment, such as the ADR425, allows a system designer to trim system errors out by setting the reference voltage to a voltage other than the nominal. The trim adjustment can be used at any temperature to trim out any error.

Long-term drift is a measure of how much the reference output voltage drifts over time. A reference with a tight long-term drift specification ensures that the overall solution remains relatively stable over its entire lifetime.

The temperature coefficient of a reference’s output voltage affects INL, DNL, and TUE. A reference with a tight temperature coefficient specification should be chosen to reduce the dependence of the DAC output voltage to ambient temperature.

In high accuracy applications, which have a relatively low noise budget, reference output voltage noise must be considered. Choosing a reference with as low an output noise voltage as practical for the system resolution required is important. Precision voltage references such as the ADR435 (XFET design) produce low output noise in the 0.1 Hz to 10 Hz region. However, as the circuit bandwidth increases, filtering the output of the reference may be required to minimize the output noise.

DRIVING INDUCTIVE LOADS

When driving inductive or poorly defined loads, a capacitor may be required between I

0.01 µF capacitor between I a load of 50 mH. The capacitive component of the load may cause slower settling, although this may be masked by the settling time of the AD5757. There is no maximum capacitance limit for the current output of the AD5757.

and AGND to ensure stability. A

OUT_x

and AGND ensures stability of

OUT_x

Table 34. Recommended Precision References

Initial Accuracy

Part No.

ADR445 ±2 50 3 2.25 ADR02 ±3 50 3 10 ADR435 ±2 40 3 8 ADR395 ±5 50 9 8 AD586 ±2.5 15 10 4

(mV Maximum)

Long-Term Drift (ppm Typical) Temperature Drift (ppm/°C Maximum)

0.1 Hz to 10 Hz Noise (μV p-p Typical)

Rev. B | Page 40 of 44

Data Sheet AD5757

TRANSIENT VOLTAGE PROTECTION

The AD5757 contains ESD protection diodes that prevent damage from normal handling. The industrial control environment can, however, subject I/O circuits to much higher transients. To protect the AD5757 from excessively high voltage transients, external power diodes and a surge current limiting resistor (R are required, as shown in Figure 63. A typical value for R The two protection diodes and the resistor (R

) must have appro-

is 10 Ω.

priate power ratings.

(FROM

DC-TO-DC

CONVERTER)

FILTER

10Ω

DCDC

4.7µF

Figure 63. Output Transient Voltage Protection

FILTER

0.1µF

AD5757

BOOST_x

OUT_x

AGND

LOAD

Additional protection can be provided using transient voltage suppressors (TVSs), also referred to as transorbs. These components are available as unidirectional suppressors, which protect against positive high voltage transients, and as bidirectional suppressors, which protect against both positive and negative high voltage transients. Transient voltage suppressors are available in a wide range of standoff and breakdown voltage ratings. The TVS should be sized with the lowest breakdown voltage possible while not conducting in the functional range of the current output.

It is recommended that all field connected nodes be protected.

MICROPROCESSOR INTERFACING

Microprocessor interfacing to the AD5757 is via a serial bus that uses a protocol compatible with microcontrollers and DSP processors. The communications channel is a 3-wire minimum interface consisting of a clock signal, a data signal, and a latch signal. The AD5757 requires a 24-bit data-word with data valid on the falling edge of SCLK.

The DAC output update is initiated on either the rising edge of

or, if

LDAC

is held low, on the rising edge of

LDAC contents of the registers can be read using the readback function.

AD5757-TO-ADSP-BF527 INTERFACE

The AD5757 can be connected directly to the SPORT interface of the ADSP-BF527, an Analog Devices, Inc., Blackfin® DSP. Figure 64 shows how the SPORT interface can be connected to control the AD5757.

SYNC

. The

Rev. B | Page 41 of 44

SPORT_TFS

SPORT_TSCK

SPORT_DTO

)

ADSP-BF527

Figure 64. AD5757-to-ADSP-BF527 SPORT Interface

GPIO0

LAYOUT GUIDELINES

Grounding

In any circuit where accuracy is important, careful consideration of the power supply and ground return layout helps to ensure the rated performance. The printed circuit board on which the AD5757 is mounted should be designed so that the analog and digital sections are separated and confined to certain areas of the

09225-013

board. If the AD5757 is in a system where multiple devices require an AGND-to-DGND connection, the connection should be made at one point only. The star ground point should be established as close as possible to the device.

The GNDSW

and ground connection for the AVCC supply are

referred to as PGND. PGND should be confined to certain areas of the board, and the PGND-to-AGND connection should be made at one point only.

Supply Decoupling

The AD5757 should have ample supply bypassing of 10 µF in parallel with 0.1 µF on each supply located as close to the package as possible, ideally right up against the device. The 10 µF capacitors are the tantalum bead type. The 0.1 µF capacitor should have low effective series resistance (ESR) and low effective series inductance (ESL), such as the common ceramic types, which provide a low impedance path to ground at high frequencies to handle transient currents due to internal logic switching.

Traces

The power supply lines of the AD5757 should use as large a trace as possible to provide low impedance paths and reduce the effects of glitches on the power supply line. Fast switching signals such as clocks should be shielded with digital ground to prevent radiating noise to other parts of the board and should never be run near the reference inputs. A ground line routed between the SDIN and SCLK lines helps reduce crosstalk between them (not required on a multilayer board that has a separate ground plane, but separating the lines helps). It is essential to minimize noise on the REFIN line because it couples through to the DAC output.

Avoid crossover of digital and analog signals. Traces on opposite sides of the board should run at right angles to each other. This reduces the effects of feedthrough on the board. A microstrip technique is by far the best but not always possible with a double-sided board. In this technique, the component side of the board is dedicated to ground plane, whereas signal traces are placed on the solder side.

SYNC

SCLK

SDIN

LDAC

AD5757

09225-080

AD5757 Data Sheet

DC-to-DC Converters

To achieve high efficiency, good regulation, and stability, a welldesigned printed circuit board layout is required.

Follow these guidelines when designing printed circuit boards (see Figure 56):

• Keep the low ESR input capacitor, C

, close to AVCC

and PGND.

• Keep the high current path from C

, to SWX and PGND as short as possible.

DCDC

• Keep the high current path from C

rectifier, D

, to the output capacitor, C

DCDC

through the inductor,

through L

DCDC

and the

DCDC

, as short as

possible.

• Keep high current traces as short and as wide as possible.

The path from C

through the inductor, L

, to SWX and

DCDC

PGND should be able to handle a minimum of 1 A.

• Place the compensation components as close as possible to

DCDC_x

COMP

• Avoid routing high impedance traces near any node

connected to SW

or near the inductor to prevent radiated

noise injection.

GALVANICALLY ISOLATED INTERFACE

In many process control applications, it is necessary to provide an isolation barrier between the controller and the unit being controlled to protect and isolate the controlling circuitry from any hazardous common-mode voltages that may occur. Analog Devices excess of 2.5 kV. The serial loading structure of the AD5757 makes it ideal for isolated interfaces because the number of interface lines is kept to a minimum. Figure 65 shows a 4-channel isolated interface to the AD5757 using an ADuM1400. For more information, visit www.analog.com.

iCoupler® products can provide voltage isolation in

MICROCONTRO LLER

SERIAL CLOCK

SERIAL DATA

SYNC OUT

CONTROL OUT

*ADDITI ONAL PINS OM ITTED F OR CLARI TY.

ADuM1400*

OUT

ENCODE DECODE

Figure 65. Isolated Interface

TO SCLK

TO SDIN

TO SYNC

TO LDAC

09225-081

Rev. B | Page 42 of 44

Data Sheet AD5757

OUTLINE DIMENSIONS

0.60 MAX

EXPOSED PAD

(BOTTOM VIEW)

PIN 1

INDICATOR

7.25

7.10 SQ

6.95

PIN 1

INDICATOR

9.00

BSC SQ

TOP VIEW

8.75

BSC SQ

0.60

MAX

0.50

BSC

1.00

0.85

0.80

SEATING

PLANE

12° MAX

0.50

0.40

0.30

0.80 MAX

0.65 TYP

0.30

0.23

0.18

COMPLIANT TO JEDEC S TANDARDS MO-220-VMMD-4

Figure 66. 64-

Lead Lead Frame Chip Scale Package [LFCSP_VQ]

0.05 MAX

0.02 NOM

0.20 REF

7.50 REF

FOR PROPER CONNECTION O F THE EXPOSED PAD, REFER TO THE PIN CONF IGURATIO N AND FUNCTION DESCRIPTIO NS SECTION OF THIS DATA SHEET.

0.25 MIN

080108-C

9 mm × 9 mm Body, Very Thin Quad

Dimensions shown in millimeters

(CP-64-3)

ORDERING GUIDE

Model1 Resolution (Bits) Temperature Range Package Description Package Option

AD5757ACPZ 16 −40°C to +105°C 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-64-3 AD5757ACPZ-REEL7 16 −40°C to +105°C 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-64-3 EVAL-AD5757SDZ Evaluation Board

Z = RoHS Compliant Part.

Rev. B | Page 43 of 44

AD5757 Data Sheet

NOTES

Rev. B | Page 44 of 44

Datasheet AD5757 Datasheet (ANALOG DEVICES)

Specifications and Main Features

Frequently Asked Questions

User Manual

FEATURES

APPLICATIONS

GENERAL DESCRIPTION

PRODUCT HIGHLIGHTS

COMPANION PRODUCTS

FUNCTIONAL BLOCK DIAGRAM

TABLE OF CONTENTS

REVISION HISTORY

DETAILED FUNCTIONAL BLOCK DIAGRAM

SPECIFICATIONS

AC PERFORMANCE CHARACTERISTICS

TIMING CHARACTERISTICS

Timing Diagrams

ABSOLUTE MAXIMUM RATINGS

ESD CAUTION

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

TYPICAL PERFORMANCE CHARACTERISTICS

CURRENT OUTPUTS

DC-TO-DC BLOCK

REFERENCE

GENERAL

TERMINOLOGY

THEORY OF OPERATION

DAC ARCHITECTURE

Reference Buffers

POWER-ON STATE OF THE AD5757

SERIAL INTERFACE

Input Shift Register

Individual DAC Updating

Simultaneous Updating of All DACs

TRANSFER FUNCTION

REGISTERS

PROGRAMMING SEQUENCE TO WRITE/ENABLE THE OUTPUT CORRECTLY

CHANGING AND REPROGRAMMING THE RANGE

DATA REGISTERS

DAC Data Register

Gain Register

Offset Register

Clear Code Register

CONTROL REGISTERS

Main Control Register

DAC Control Register

Software Register

DC-to-DC Control Register

Slew Rate Control Register

READBACK OPERATION

Readback Example

Status Register

DEVICE FEATURES

OUTPUT FAULT

DIGITAL OFFSET AND GAIN CONTROL

STATUS READBACK DURING A WRITE

ASYNCHRONOUS CLEAR

PACKET ERROR CHECKING

INTERNAL REFERENCE

WATCHDOG TIMER

OUTPUT ALERT

EXTERNAL CURRENT SETTING RESISTOR

HART

DIGITAL SLEW RATE CONTROL

POWER DISSIPATION CONTROL

DC-TO-DC CONVERTERS

DC-to-DC Converter Operation

DC-to-DC Converter Output Voltage

DC-to-DC Converter Settling Time

DC-to-DC Converter On-Board Switch

DC-to-DC Converter Switching Frequency and Phase

DC-to-DC Converter Inductor Selection

DC-to-DC Converter External Schottky Selection

DC-to-DC Converter Compensation Capacitors

DC-to-DC Converter Input and Output Capacitor Selection

AICC SUPPLY REQUIREMENTS—STATIC

AICC SUPPLY REQUIREMENTS—SLEWING

Reducing AICC Current Requirements

EXTERNAL PMOS MODE

APPLICATIONS INFORMATION