Datasheet AD5678 Datasheet (Analog Devices)

4 x12-Bit and 4 x16-Bit Octal DAC with
On-Chip Reference in 14 Lead TSSOP
Preliminary Technical Data
FEATURES
Low Power Octal DAC with 4 DACs x 16 Bits
APPLICATIONS
ProcessControl Data Acquisition Systems Portable Battery Powered Instruments Digital Gain and Offset Adjustment Programmable Voltage and Current Sources
GENERAL DESCRIPTION
The AD5678 is a low power, octal buffered voltage-out DAC; 4 DACs with 12-bits of resolution and 4 DACs with16-bits of resolution, in a single package. All devices operate from a single +2.7V to +5.5V, and are guaranteed monotonic by design.
The AD5678 has an on-chip reference with an internal gain of two. The AD5678-1 has a 1.25V 10ppm/°C max reference and the AD5678-2, has a 2.5V 10ppm/°C max reference. The on­board reference is off at power-up allowing the use of an external reference. The internal reference is turned on by writing to the DAC. The part incorporates a power-on-reset circuit that ensures that the DAC output powers up to zero volts and remains there until a valid write takes place. The part contains a power-down feature that reduces the current consumption of the device to 200nA at 5V and provides software selectable output loads while in power-down mode for any or all DACs channels.
AD5678
Programmable Attenuators
V
I
NPUT
REGISTER
I
NPUT
REGISTER
I
NPUT
REGISTER
I
NPUT
REGISTER
I
NPUT
REGIS-
TER
I
NPUT
REGISTER
I
NPUT
REGISTER
I
NPUT
REGISTER
POWER-ON
DD
REGISTER
REGISTER
REGISTER
REGISTER
REGISTER
REGISTER
REGISTER
RESET
SCLK
SYNC
DIN
*RU-16 PACKAGE ONLY
AD5678
LDAC
INTERFACE
LOGIC
LDAC*
CLR*
Figure 1. Functional Block Diagram
The outputs of all DACs may be updated simultaneously using the /LDAC function, with the added functionality of selecting through software any number of DAC channels to synchronize. There is also an asynchronous active low /CLR that clears all DACs to a software selectable code - 0 V, midscale or fullscale .
The AD5678 utilizes a versatile three-wire serial interface that operates at clock rates up to 50 MHz and is compatible with standard SPI™, QSPI™, MICROWIRE™ and DSP interface standards. Its on-chip precision output amplifier allows rail-to­rail output swing to be achieved.
PRODUCT HIGHLIGHTS
1. Octal – 4x12-/4x16-Bit DAC; 12-Bit Accuracy
Guaranteed.
2. On-chip 1.25/2.5V, 10ppm/°C max Reference.
3. Available in 14/16-lead TSSOP package.
4. Power-On-Reset to Zero volts.
5. Power-down capability. When powered down, the
DAC typically consumes 50nA at 3V and 200nA at 5V.
DAC
DAC
DAC
D
AC
REGISTER
D
AC
D
AC
D
AC
D
AC
V
STRING
DAC A
STRING
DAC B
STRING
DAC C
STRING DAC D
STRING DAC E
STRING
DAC F
STRING DAC G
STRING
DAC H
REF
1.25/2.5V Ref
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
BUFFER
POWER-DOWN
GND
LOGIC
V
A
OUT
V
B
OUT
V
C
OUT
V
D
OUT
V
E
OUT
V
F
OUT
V
G
OUT
V
H
OUT
Rev. PrB
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other 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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 © 2005 Analog Devices, Inc. All rights reserved.
AD5678
TABLE OF CONTENTS
Features.......................................................................................... 1
Preliminary Technical Data
Terminology................................................................................ 10
Applications................................................................................... 1
General Description..................................................................... 1
Product Highlights....................................................................... 1
AD5678–Specifications.................................................................... 3
Timing Characteristics..................................................................... 8
Pin Configuration and Function Descriptions............................. 9
Absolute Maximum Ratings.......................................................... 10
ESD Caution................................................................................ 10
REVISION HISTORY
Revision 0: Initial Version
AD5678–Typical Performance Characteristics .......................... 12
General Description................................................................... 15
Serial Interface............................................................................ 15
Microprocessor Interfacing............................................................
Applications .....................................................................................
Outline Dimensions....................................................................... 22
Ordering Guide ...............................................................................
Rev.PrB | Page 2 of 22
Preliminary Technical Data
AD5678
AD5678–SPECIFICATIONS
(VDD = +4.5 V to +5.5 V; RL = 2 kΩ to GND; CL = 200 pF to GND; External REFIN = VDD; all specifications T noted)
Table 1.
A Grade
B Version
Parameter Min Typ Max Unit
STATIC PERFORMANCE
3,4
Conditions/Comments
1,2
AD5678 (DAC C, D, E, F) Resolution 12 Bits Relative Accuracy ±0.5 ±6 LSB See Figure 4 Differential Nonlinearity ±1 LSB Guaranteed Monotonic by Design. See Figure 5. AD5678 (DAC A, B, G, H) Resolution 16 Bits Relative Accuracy ±32 LSB See Figure 4 Differential Nonlinearity ±1 LSB Guaranteed Monotonic by Design. See Figure 5. Load Regulation 2 LSB/mA
VDD=Vref=5V, Midscale
sourcing/sinking Zero Code Error +1 +9 mV All Zeroes Loaded to DAC Register. See Figure 8. Zero Code Error Drift3 ±20 µV/°C Full-Scale Error -0.15 -1.25 % of FSR All Ones Loaded to DAC Register. See Figure 8. Gain Error ±0.7 % of FSR Gain Temperature Coefficient ±5 ppm of FSR/°C Offset Error ±1 ±9 mV Offset Temperature Coefficient 1.7 µV/°C
DC Power Supply Rejection Ratio6
DC Crosstalk6 (Ext Ref)
DC Crosstalk6 (Int Ref)
10
4.5
10
20
4.5
20
–80
dB VDD ±10%
µV µV/mA µV µV µV/mA µV
RL = 2 k. to GND or VDD
Due to Load current change
Due to Powering Down (per channel)
RL = 2 k. to GND or VDD
Due to Load current change
Due to Powering Down (per channel)
OUTPUT CHARACTERISTICS6 Output Voltage Range 0 VDD V Capacitive Load Stability 2 pF RL=∞ 10 pF RL=2 kΩ DC Output Impedance 0.5 Short Circuit Current 30 mA VDD=+5V Power-Up Time 4 µs Coming out of Power-Down Mode. VDD=+5V
REFERENCE INPUTS3
Reference Input voltage
Reference Current 35 45 µ A V
VDD
V ±1% for specified performance
= VDD = +5.5V (per DAC channel)
REF
1
Temperature ranges are as follows: B Version: -40°C to +125°C, typical at 25°C.
2
Linearity calculated using a reduced code range of 485 to 64714. Output unloaded.
3
DC specifications tested with the outputs unloaded unless stated otherwise.
4
Linearity is tested using a reduced code range: AD5628 (Code 48 to Code 4047), AD5648 (Code / to Code /), and AD5678 (Code 485 to 64714).
6
Guaranteed by design and characterization; not production tested.
8
Interface inactive. All DACs active. DAC outputs unloaded.
9
All eight DACs powered down.
Specifications subject to change without notice.
MIN
to T
unless otherwise
MAX
Iout=0mA to 15mA
Rev. PrB| Page 3 of 22
AD5678
A Grade
Parameter Min Typ Max Unit
Reference Input Range 0 VDD
Reference Input Impedance 14.6
REFERENCE OUTPUT Output Voltage AD5678x-2/3 2.495 2.5 2.505 V Reference TC ±10 ppm/°C Reference Output Impedance 2
LOGIC INPUTS3 Input Current ±1 µA V
, Input Low Voltage 0.8 V VDD=+5 V
INL
V
, Input High Voltage 2 V VDD=+5 V
INH
Pin Capacitance 3 pF POWER REQUIREMENTS VDD 4.5 5.5 V All Digital Inputs at 0 or VDD IDD (Normal Mode)8 DAC Active and Excluding Load Current VDD=4.5 V to +5.5 V 2 4 mA VIH=VDD and VIL=GND IDD (All Power-Down Modes)9 VDD=4.5 V to +5.5 V 0.2 1 µA VIH=VDD and VIL=GND POWER EFFICIENCY I
89 % I
OUT/IDD
k
k
Preliminary Technical Data
B Version Conditions/Comments
Per DAC channel
LOAD
1,2
=2 mA, VDD=+5 V
Rev.PrB | Page 4 of 22
Preliminary Technical Data
1
AC CHARACTERISTICS
specifications T
MIN
to T
unless otherwise noted)
MAX
(VDD = +4.5 V to +5.5 V; RL = 2 kΩ to GND; CL = 200 pF to GND; External REFIN = VDD; all
AD5678
Parameter2 Min Typ Max Unit
Output Voltage Settling Time AD5678 (DAC C, D, E, F) 6 8 µs ¼ to ¾ scale settling to ±2LSB AD5678 (DAC A, B, G, H) 8 10 µs ¼ to ¾ scale settling to ±2LSB Settling Time for 1LSB Step Slew Rate 1.5 V/µs Digital-to-Analog Glitch Impulse 5 nV-s 1 LSB Change Around Major Carry. See Figure 21. Channel –to-Channel Isolation 100 dB Digital Feedthrough 0.1 nV-s Digital Crosstalk 0.5 nV-s Analog Crosstalk 1 nV-s DAC-to-DAC Crosstalk 3 nV-s Multiplying Bandwidth 200 kHz VREF = 2V ± 0.1 V p-p. Total Harmonic Distortion -80 dB VREF = 2V ± 0.1 V p-p. Frequency = 10kHz Output Noise Spectral Density 120 nV/√Hz DAC code=8400H, 1kHz 100 nV/√Hz DAC code=8400H, 10kHz Output Noise 15
1
µVp-p
B Version Conditions/Comments
0.1Hz to 10Hz;
NOTES
1Guaranteed by design and characterization; not production tested. 2See the Terminology section. 3Temperature range (Y Version): –40°C to +125°C; typical at +25°C.
Specifications subject to change without notice.
Rev. PrB| Page 5 of 22
AD5678
Preliminary Technical Data
AD5678–SPECIFICATIONS
(VDD = +2.7 V to +3.6 V; RL = 2 kΩ to GND; CL = 200 pF to GND; External REFIN = VDD; all specifications T noted)
Table 2
A Grade
B Version
Parameter Min Typ Max Unit
STATIC PERFORMANCE AD5678 (DAC C, D, E, F) Resolution 12 Bits Relative Accuracy ±0.5 ±6 LSB See Figure 4 Differential Nonlinearity ±1 LSB Guaranteed Monotonic by Design. See Figure 5. AD5678 (DAC A, B, G, H) Resolution 16 Bits Relative Accuracy ±32 LSB See Figure 4 Differential Nonlinearity ±1 LSB Guaranteed Monotonic by Design. See Figure 5. Load Regulation 4 LSB/mA
Zero Code Error +1 +9 mV All Zeroes Loaded to DAC Register. See Figure 8. Zero Code Error Drift1 ±20 µV/°C Full-Scale Error -0.15 -1.25 % of FSR All Ones Loaded to DAC Register. See Figure 8. Gain Error ±0.7 % of FSR Gain Temperature Coefficient ±5 ppm of FSR/°C Offset Error ±1 ±9 mV Offset Temperature Coefficient 1.7 µV/°C
DC Power Supply Rejection Ratio6
DC Crosstalk6 (Ext Ref)
DC Crosstalk6 (Int Ref)
OUTPUT CHARACTERISTICS6 Output Voltage Range 0 VDD V Capacitive Load Stability 2 pF RL=∞ 10 pF RL=2 kΩ DC Output Impedance 0.5 Short Circuit Current 30 mA VDD=+3V Power-Up Time 5 µs Coming Out of Power-Down Mode. VDD=+3V
REFERENCE INPUTS3
Reference Input voltage VDD V ±1% for specified performance
Reference Current 20 20 µ A V
Reference Input Range 0 VDD
Reference Input Impedance 14.6
REFERENCE OUTPUT Output Voltage AD5678x-1 1.248 1.25 1.252 V Reference TC ±10 ppm/°C
3,4
–80
10
4.5
10
20
4.5
20
dB VDD = ±10%
µV µV/mA µV µV µV/mA µV
k
Conditions/Comments
VDD=Vref=3V, Midscale
sourcing/sinking
RL = 2 k. to GND or VDD
Due to Load current change
Due to Powering Down (per channel)
RL = 2 k. to GND or VDD
Due to Load current change
Due to Powering Down (per channel)
REF
Per DAC channel
1,1
= VDD = +3.6V (per DAC channel)
MIN
to T
unless otherwise
MAX
Iout=0mA to 7.5mA
Rev.PrB | Page 6 of 22
Preliminary Technical Data
AD5678
Reference Output Impedance 2
k
LOGIC INPUTS3 Input Current ±1 µA V
, Input Low Voltage 0.8 V VDD=+3 V
INL
V
, Input High Voltage 2 V VDD=+3 V
INH
Pin Capacitance 3 pF POWER REQUIREMENTS VDD 2.7 3.6 V All Digital Inputs at 0 or VDD IDD (Normal Mode)8 DAC Active and Excluding Load Current VDD=2.7 V to +3.6 V 2 4 mA VIH=VDD and VIL=GND IDD (All Power-Down Modes)9 VDD=2.7 V to +3.6 V 0.2 1 µA VIH=VDD and VIL=GND POWER EFFICIENCY I
89 % I
OUT/IDD
=2 mA, VDD=+5 V
LOAD
AC CHARACTERISTICS1
(VDD = +2.7 V to +3.6 V; RL = 2 kΩ to GND; CL = 200 pF to GND; External REFIN = VDD; all specifications T noted)
B Version
Parameter2 Min Typ Max Unit
Conditions/Comments
1
Output Voltage Settling Time AD5678 (DAC C, D, E, F) 6 8 µs ¼ to ¾ scale settling to ±2LSB AD5678 (DAC A, B, G, H) 8 10 µs ¼ to ¾ scale settling to ±2LSB Settling Time for 1LSB Step Slew Rate 1.5 V/µs Digital-to-Analog Glitch Impulse 10 nV-s 1 LSB Change Around Major Carry. See Figure 21. Channel –to-Channel Isolation 100 dB Digital Feedthrough 0.5 nV-s Digital Crosstalk 0.5 nV-s Analog Crosstalk 1 nV-s DAC-to-DAC Crosstalk 3 nV-s Multiplying Bandwidth 200 kHz VREF = 2V ± 0.1 V p-p. Total Harmonic Distortion -80 dB VREF = 2V ± 0.1 V p-p. Frequency = 10kHz Output Noise Spectral Density 120 nV/√Hz DAC code=8400H, 1kHz 100 nV/√Hz DAC code=8400H, 10kHz Output Noise 15
NOTES
1Guaranteed by design and characterization; not production tested. 2See the Terminology section. 3Temperature range (Y Version): –40°C to +125°C; typical at +25°C.
Specifications subject to change without notice.
µVp-p
0.1Hz to 10Hz;
MIN
to T
unless otherwise
MAX
Rev. PrB| Page 7 of 22
AD5678
Preliminary Technical Data
TIMING CHARACTERISTICS
All input signals are specified with tr = tf = 1 ns/V (10% to 90% of VDD) and timed from a voltage level of (VIL + VIH)/2.
See Figure 2.
= +2.7 V to +5.5 V; all specifications T
(V
DD
Limit at T
Parameter V
= 2.7 V to 3.6 V VDD= 3.6 V to 5.5 V Unit Conditions/Comments
DD
MIN
to T
MIN
unless otherwise noted)
MAX
, T
MAX
t1 1 20 20 ns min SCLK Cycle Time t2 11 9 ns min SCLK High Time
t3 9 9 ns min SCLK Low Time t4 13 13 ns min
SYNC
to SCLK Falling Edge Setup Time t5 4 4 ns min Data Setup Time t6 4 4 ns min Data Hold Time t7 0 0 ns min
t8 25 20 ns min t9 13 13 ns min t10 0 0 ns min t11 20 20 ns min t12 20 20 ns min
SCLK Falling Edge to Minimum SYNC
SYNC
Rising Edge to SCLK Fall Ignore
SCLK Falling Edge to
LDAC Pulsewidth Low
SCLK Falling Edge to LDAC Rising Edge
SYNC
High Time
SYNC
Rising Edge
Fall Ignore
t13 20 20 ns min /CLR Pulse Width Low t14 0 0 ns min
SCLK Falling Edge to LDAC Falling Edge
t15 tbd tbd ns min /CLR Pulse Activation Time (AD5380?)
t
10
SCLK
t
8
SYNC
DIN
LDAC1
LDAC2
CLR
NOTES
1. ASYNCHRONOUS LDAC UPDATE MODE.
2. SYNCHRONOUS LDAC UPDATE MODE.
DB31
t
4
t
6
t
5
t
1
t
t
3
2
DB0
t
t14
t
9
7
t11
Figure 2. Serial Write Operation
1
3Maximum SCLK frequency is 50 MHz at VDD = +3.6 V to +5.5 V and 20 MHz at VDD = +2.7 V to +3.6 V.
t12
t13
Rev.PrB | Page 8 of 22
Preliminary Technical Data
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
AD5678
V V V
V
SYNC
V
OUT OUT OUT
OUT
V
REF
DD
A C E
G
1 2
AD5678
3 4
TOP VIEW
(Not to Scale)
5 6 7
14
SCLK
13
DIN
12
GND
11
V
B
OUT
V
D
10
OUT
9
V
F
OUT
8
V
H
OUT
V
V V V
OUT
LDAC
SYNC
V OUT OUT
OUT
V
REF
DD
A C E
G
1
AD5678
2 3
4
TOP VIEW
(Not to Scale)
5 6 7 8
16
SCLK
15
DIN
14
GND
V
B
13
OUT
V
D
12
OUT
11
V
F
OUT
V
H
10
OUT
9
CLR
Figure 3. 14-Lead TSSOP (RU-14) Figure 4. 16-Lead TSSOP (RU-16)
Table 2. Pin Function Descriptions
Pin No. Mnemonic Function
1 /LDAC Pulsing this pin low allows any or all DAC registers to be updated if the input registers have new data.
This allows simultaneous update of all DAC outputs. Alternatively, this pin can be tied permanently low.
2 /SYNC
Active Low-Control Input. This is the frame synchronization signal for the input data. When SYNC goes low, it powers on the SCLK and DIN buffers and enables the input shift register. Data is transferred in on the falling edges of the following 32 clocks. If SYNC is taken high before the 32nd falling edge, the rising edge of SYNC acts as an interrupt and the write sequence is ignored by the device.
3 VDD Power Supply Input. These parts can be operated from 2.5 V to 5.5 V, and the supply should be
decoupled with a 10 µF capacitor in parallel with a 0.1 µF capacitor to GND.
4 VOUTA Analog Output Voltage from DAC A. The output amplifier has rail-to-rail operation.
13 VOUTB Analog Output Voltage from DAC B. The output amplifier has rail-to-rail operation.
5 VOUTC Analog Output Voltage from DAC C. The output amplifier has rail-to-rail operation.
12 VOUTD Analog Output Voltage from DAC D. The output amplifier has rail-to-rail operation.
8 VREF Reference Input/Output Pin
9 /CLR
Active Low Control Input that Loads Software selectable code – Zero, midscale, fullscale - to All Input and DAC Registers. Therefore, the outputs also go to selected code. Default clears the output to 0V.
6 VOUTE Analog Output Voltage from DAC E. The output amplifier has rail-to-rail operation.
11 VOUTF Analog Output Voltage from DAC F. The output amplifier has rail-to-rail operation.
7 VOUTG Analog Output Voltage from DAC G. The output amplifier has rail-to-rail operation.
10 VOUTH Analog Output Voltage from DAC H. The output amplifier has rail-to-rail operation.
14 GND Ground Reference Point for All Circuitry on the Part.
15 DIN Serial Data Input. This device has a 32-bit shift register. Data is clocked into the register on the falling
edge of the serial clock input.
16 SCLK Serial Clock Input. Data is clocked into the input shift register on the falling edge of the serial clock
input. Data can be transferred at rates up to 50 MHz.
Rev. PrB| Page 9 of 22
AD5678
Preliminary Technical Data
ABSOLUTE MAXIMUM RATINGS
V
to GND -0.3 V to VDD + 0.3 V
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 listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
= +25°C unless otherwise noted)
(T
A
Parameter Rating
VDD to GND -0.3 V to +7 V Digital Input Voltage to GND -0.3 V to VDD + 0.3 V
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
TERMINOLOGY
Relative Accuracy
For the DAC, relative accuracy or Integral Nonlinearity (INL) is a measure of the maximum deviation, in LSBs, from a straight line passing through the endpoints of the DAC transfer function. A typical INL vs. code plot can be seen in Figure 2.
Differential Nonlinearity
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 can be seen in Figure 3.
OUT
Operating Temperature Range Industrial (B Version) -40°C to +105°C Storage Temperature Range -65°C to +150°C Junction Temperature (TJ Max) +150°C TSSOP Package Power Dissipation (TJ Max-TA)/θJA θJA Thermal Impedance 150.4°C/W Lead Temperature, Soldering Vapor Phase (60 sec) +215°C Infrared (15 sec) +220°C
(0000Hex) is loaded to the DAC register. Ideally the output should be 0 V. The zero-code error is always positive in the AD5660 because the output of the DAC cannot go below 0 V. It is due to a combination of the offset errors in the DAC and output amplifier. Zero-code error is expressed in mV. A plot of zero-code error vs. temperature can be seen in Figure 6.
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 ideal expressed as a percent of the full-scale range.
Zero-Code Error Drift
This is a measure of the change in zero-code error with a change in temperature. It is expressed in µV/°C.
Offset Error
Offset error is a measure of the difference between VOUT (actual) and VOUT (ideal) expressed in mV in the linear region of the transfer function. Offset error is measured on the AD5678 with Code 512 loaded into the DAC register.
This is a measure of the offset error of the DAC and the output amplifier (see Figures 2 and 3). It can be negative or positive, and is expressed in mV.
Zero-Code Error
Zero-code error is a measure of the output error when zero code
Rev.PrB | Page 10 of 22
Gain Error Drift
This is a measure of the change in gain error with changes in temperature. It is expressed in (ppm of full-scale range)/°C.
Full-Scale Error
Full-scale error is a measure of the output error when full-scale code (FFFF Hex) is loaded to the DAC register. Ideally the output should be VDD – 1 LSB. Full-scale error is expressed in percent of
full-scale range. A plot of full-scale error vs. temperature can be seen in Figure 6.
Total Unadjusted Error
Total Unadjusted Error (TUE) is a measure of the output error
Preliminary Technical Data
taking the various offset and gain errors into account. A typical TUE vs. code plot can be seen in Figure 4.
AD5678
change on the digital input pins, i.e., from all 0s to all 1s and vice versa.
Digital-to-Analog Glitch Impulse
Digital-to-analog glitch impulse is the impulse injected into the analog output when the input code in the DAC register changes state. It is normally specified as the area of the glitch in nV secs and is measured when the digital input code is changed by 1 LSB at the major carry transition (7FFF Hex to 8000 Hex). See Figure 19.
DC Power Supply Rejection Ratio (PSRR)
This indicates how the output of the DAC is affected by changes in the supply voltage. PSRR is the ratio of the change in VOUT to a change in VDD for full-scale output of the DAC. It is measured in dB. VREF is held at 2 V and VDD is varied ±10%.
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. It is expressed in µV.
Reference Feedthrough
This is the ratio of the amplitude of the signal at the DAC output to the reference input when the DAC output is not being updated (i.e., LDAC is high). It is expressed in dB.
Channel-to-Channel Isolation
This is the ratio of the amplitude of the signal at the output of one DAC to a sine wave on the reference input of another DAC. It is measured in dB.
Digital Feedthrough
Digital feedthrough is a measure of the impulse injected into the analog output of a DAC from the digital input pins of the device, but is measured when the DAC is not being written to (SYNC held high). It is specified in nV-s and is measured with a fullscale
Digital Crosstalk
This is the glitch impulse transferred to the output of one DAC at midscale in response to a full-scale code change (all 0s to all 1s and vice versa) in the input register of another DAC. It is measured in standalone mode and is expressed in nV-s.
Analog Crosstalk
This is the glitch impulse transferred to the output of one DAC due to a change in the output of another DAC. It is measured by loading one of the input registers with a full-scale code change (all 0s to all 1s and vice versa) while keeping LDAC high. Then pulse LDAC low and monitor the output of the DAC whose digital code was not changed. The area of the glitch is expressed in nV-s.
DAC-to-DAC Crosstalk
This is the glitch impulse transferred to the output of one DAC due to a digital code change and subsequent output change of another DAC. This includes both digital and analog crosstalk. It is measured by loading one of the DACs with a full-scale code change (all 0s to all 1s and vice versa) with LDAC low and monitoring the output of another DAC. The energy of the glitch is expressed in nV-s.
Multiplying Bandwidth
The amplifiers within the DAC have a finite bandwidth. The multiplying bandwidth is a measure of this. A sine wave on the reference (with full-scale code loaded to the DAC) appears on the output. The multiplying bandwidth is the frequency at which the output amplitude falls to 3 dB below the input.
Total Harmonic Distortion
This is the difference between an ideal sine wave and its attenuated version using the DAC. The sine wave is used as the reference for the DAC, and the THD is a measure of the harmonics present on the DAC output. It is measured in dB.
Rev. PrB| Page 11 of 22
AD5678
AD5678–TYPICAL PERFORMANCE CHARACTERISTICS
Figure 4. Typical INL Plot
Preliminary Technical Data
Figure 7. INL Error and DNL Error vs. Temperature
Figure 5. Typical DNL Plot
Figure 6. Typical Total Unadjusted Error Plot
Rev.PrB | Page 12 of 22
Figure 8. Zero-Scale Error and Full-Scale Error vs. Temperature
Figure 9. I
Histogram with VDD=3V and VDD=5V
DD
Preliminary Technical Data
AD5678
Figure 10. Source and Sink Current Capability with V
Figure 11. Source and Sink Current Capability with V
DD
DD
=3V
=5 V
Figure 13. Supply Current vs. Temperature
Figure 14. Supply Current vs. Supply Voltage
Figure 12. Supply Current vs. Code
Rev. PrB| Page 13 of 22
Figure 15. Power-Down Current vs. Supply Voltage
AD5678
Figure 16. Supply Current vs. Logic Input Voltage
Preliminary Technical Data
Figure 19. Power-On Reset to 0V
Figure 20. Exiting Power-Down (800 Hex Loaded)
Figure 17. Full-Scale Settling Time
Figure 18. Half-Scale Settling Time
Figure 21. Digital-to-Analog Glitch Impulse
Rev.PrB | Page 14 of 22
Preliminary Technical Data
GENERAL DESCRIPTION
D/A Section
The AD5678 DACs are fabricated on a CMOS process. The architecture consists of a string DAC followed by an output buffer amplifier. The parts include an internal 1.25/2.5V, 10ppm/°C reference with an internal gain of two. Figure 22 shows a block diagram of the DAC architecture.
V
DD
REF (+)
DAC REGISTER
Figure 22. DAC Architecture
Since the input coding to the DAC is straight binary, the ideal output voltage is given by:
OUT
OUT
where D = decimal equivalent of the binary code that is loaded to the DAC register; 0 - 4095 for AD5678 -DAC C, D, E, F (12 bit) 0 - 65535 for AD5678 -DAC A, B, G, H (16 bit)
N = the DAC resolution
RESISTOR
STRING
REF ()
GND
extVrefV
)(
×=
⎜ ⎝
VrefV
(int)2
×=
OUTPUT
AMPLIFIER
(Gain=2)
D
⎞ ⎟
^2
N
D
⎛ ⎜
⎞ ⎟
^2
N
V
OUT
AD5678
Figure 23. Resistor String
Resistor String
The resistor string section is shown in Figure 23. It is simply a string of resistors, each of value R. The code loaded to the DAC register determines at which node on the string the voltage is tapped off to be fed into the output amplifier. The voltage is tapped off by closing one of the switches connecting the string to the amplifier. Because it is a string of resistors, it is guaranteed monotonic.
Output Amplifier
The output buffer amplifier is capable of generating rail-to-rail voltages on its output which gives an output range of 0 V to V
DD
pF to GND. The source and sink capabilities of the output amplifier can be seen in Figure 10 and Figure 11. The slew rate is 1.5 V/µs with a half-scale settling time of 8 µs with the output unloaded.
SERIAL INTERFACE
The AD5678 has a three-wire serial interface ( DIN), which is compatible with SPI, QSPI and MICROWIRE interface standards as well as most DSPs. See Figure 2 for a timing diagram of a typical write sequence.
The write sequence begins by bringing the from the DIN line is clocked into the 32-bit shift register on the falling edge of SCLK. The serial clock frequency can be as high as 50 MHz, making the AD5678 compatible with high speed DSPs. On the 32nd falling clock edge, the last data bit is clocked in and the programmed function is executed (i.e., a change in
Rev. PrB| Page 15 of 22
. It is capable of driving a load of 2 kΩ in parallel with 1000
SYNC
, SCLK and
SYNC
line low. Data
AD5678
DAC register contents and/or a change in the mode of operation). At this stage, the
SYNC
line may be kept low or be brought high. In either case, it must be brought high for a minimum of 33 ns before the next write sequence so that a falling edge of
SYNC
the does when V
SYNC
can initiate the next write sequence. Since
buffer draws more current when VIN = 2V than it
= 0.8 V,
IN
SYNC
should be idled low between write sequences for even lower power operation of the part. As is mentioned above, however, it must be brought high again just before the next write sequence.
C3 C2 C1 C0 A3 A2 A1 A0 D15 D14 D13 D1 2 D11 D10 D9 D8 D 7 D6 D5 D4 D3 D2 D1 D 0 X X X XXXX X
Preliminary Technical Data
Input Shift Register
The input shift register is 32 bits wide (see Figure 24, 25). The first four bits are “don’t cares.” The next four bits are the Command bits C3-C0, (see Table 1) followed by the 4-bit DAC address A3-A0, (see Table 2) and finally the 16 /12bit data word. The data word comprises the 16- 12- bit input code followed by 4 or 8 don’t care bits, for the AD5678 (DAC A, B, G, H) and AD5628 (DAC C, D, E, F) respectively. See figure 24 and 25. These data bits are transferred to the DAC register on the 32nd falling edge of SCLK.
DB0 (LSB)
COMMAND BITS
ADDRE SS BITS
Figure 24 AD5678. Input Register Content for DAC A, B, G , H
C3 C2 C1 C0 A3 A2 A1 A0 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X X X X XXXX X
COMMAND BITS
ADDRE SS BITS
Figure 25 AD5678. Input Register Content for DAC C, D, E, F
Command
C3 C2 C1 C0
0 0 0 0 Write to Input Register n
0 0 0 1 Update DAC Register n
0 0 1 0 Write to Input Register n,
Update All
DB0 (LSB)
0 0 1 1 Write to and Update DAC
channel n
0 1 0 0 Power Down DAC
(Power-up)
Rev.PrB | Page 16 of 22
Preliminary Technical Data
0 1 0 1 Load Clear Code Register
0 1 1 0 Load LDAC Register
(LDAC overwrite)
0 1 1 1 Reset (Power-on-Reset)
1 0 0 0 REF Setup Register
1 0 0 1 Reserved
* * * * Reserved
1 1 1 1 Reserved
Table 1. Command Definition
ADDRESS (n)
A3 A2 A1 A0
0 0 0 0 DAC A (16 bit)
AD5678
0 0 0 1 DAC B (16 bit)
0 0 1 0 DAC C (12 bit)
0 0 1 1 DAC D (12 bit)
0 1 0 0 DAC E (12 bit)
0 1 0 1 DAC F (12 bit)
0 1 1 0 DAC G (16 bit)
0 1 1 1 DAC H (16 bit)
1 1 1 1 All DACs
Table2. Address Command
SYNC
Interrupt
In a normal write sequence, the rising edge of SYNC . However, if
SYNC
line is kept low for 32 falling edges of SCLK and the DAC is updated on the 32nd falling edge and
SYNC
is brought high before the 32nd falling edge this acts as an interrupt to the write sequence. The shift register is reset and the write sequence is seen as invalid. Neither an update of the DAC register contents or a change in the operating mode occurs—see Figure 25.
SCLK
SYN C
DIN
DB31
INVALID WRITE SEQUENCE:
SYN C HIGH BEFORE 32NDFALLING EDGE
DB0
DB31 DB0
VALID WRITE SEQUENCE, OUTPUT UPDATES
ON THE 32NDFALLING EDGE
Figure 25. SYNC Interrupt Facility
Rev. PrB| Page 17 of 22
AD5678
Reference Setup –External to Internal
The on-board reference is turned off at power-up by default, allowing the use of an external reference. The AD5678 has an on-chip reference with an internal gain of two. The AD56x8-1 has a 1.25V 10ppm/°C max reference and the AD56x8-2, has a 2.5V 10ppm/°C max reference. The on-board reference can be turned on/off through a software executable REF Setup function, Command 1000 is reserved for this REF Setup function, see Table 3. The reference mode is software-programmable by setting a bit (DB0) in the REF Setup register. Table 4 shows how the state of the bits corresponds to the mode of operation of the device.
Table 3. Reference Set-up Register
Preliminary Technical Data
REF Setup Register (DB0)
0 Ref Off (Default)
1 Ref On
MSB LSB
DB31 – DB28
x 1 0 0 0 x x x x x 1/0
Don’t Cares
Table 4 32-Bit Input Shift Register Contents for Reference Setup Function
DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB1-
COMMAND BITS (C3-C0) ADDRESS BITS (A3 – A0) Don’t
Action
DB19
Cares
DB0
REF Setup Register
Power-On-Reset
The AD5678 family contains a power-on-reset circuit that controls the output voltage during power-up. The AD5678 output powers up to zero and the output remains there until a valid write sequence is made to the DAC. This is useful in applications where it is important to know the state of the output of the DAC while it is in the process of powering up. There is also a software executable Reset function that will reset the DAC to the Power-on -Reset code. Command 0111 is reserved for this Reset function, see Table 1.
Power-Down Modes
The AD5678 contains four separate modes of operation. Command 0100 is reserved for the Power-Down function. See Table 1. These modes are software-programmable by setting two bits (DB9 and DB8) in the control register. Table 5 shows how the state of the bits corresponds to the mode of operation of the device. Any or all DACs, (DacH to DacA) may be powered down to the selected mode by setting the corresponding 8 bits (DB7 to DB0) to a “1”. See Table 6 for contents of the Input Shift Register during power down/up operation.
When both bits are set to 0, the part works normally with its normal power consumption of 250 µA at 5 V. However, for the three power­down modes, the supply current falls to 200 nA at 5 V (50 nA at 3 V). Not only does the supply current fall but the output stage is also internally switched from the output of the amplifier to a resistor network of known values. This has the advantage that the output impedance of the part is known while the part is in power-down mode. There are three different options. The output is connected
Rev.PrB | Page 18 of 22
Preliminary Technical Data
AD5678
internally to GND through a 1 kΩ resistor, a 100 kΩ resistor or it is left open-circuited (Three-State). The output stage is illustrated in figure 24.
The bias generator of selected DAC(s), the output amplifier, the resistor string and other associated linear circuitry are all shut down when the power-down mode is activated. However, the contents of the DAC register are unaffected when in power-down. The time to exit power-down is typically (2.5 µs for V
= 5 V and 5 µs for VDD = 3 V). See Figure 20 for a plot.
DD
Any combination of DACs can be powered up by setting PD1 and PD0 to “0” (normal operation). Output powers-up to value in input register (/LDAC Low) or to value in DAC register before Power-Down (/LDAC High).
DB9 DB8 Operating Mode
0 0 Normal Operation Power Down Modes 0 1 1 kΩ to GND 1 0 100 kΩ to GND 1 1 Three State
Table 5. Modes of Operation for the AD5678
MSB LSB
DB31 – DB28
x 0 1 0 0 x x x x x PD1 PD0 DacH DacG DacF DacE DacD DacC DacB DacA
Don’t Cares
DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB10—
COMMAND BITS (C2-C0) ADDRESS BITS (A3 – A0)
Don’t cares
DB19
Don’t Cares
DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
Power Down Mode
Power Down/Up Channel Selection – Set Bit to a “1” to select
Table 6. 32-Bit Input Shift Register Contents for Power Down/Up Function
Clear Code Register
The AD5678 gives the option of clearing all DAC channels to 0, midscale or fullscale code. Command 0101 is reserved for the Clear Code function. See Table1. These clear code values are software-programmable by setting two bits (DB1 and DB0) in the control register. Table shows how the state of the bits corresponds to the clear code values of the device. Upon execution of the hardware /CLR pin (active LOW), the DAC output is cleared to the clear code register value (default setting is zero). See Table 8 for contents of the Input Shift Register during the Clear Code Register operation
Clear Code Register
CR1 CR0 Clears to code
Rev. PrB| Page 19 of 22
AD5678
0 0 0000h
0 1 8000h
1 0 FFFFh
1 1 No operation
Table 7. Clear Code Register
MSB LSB
Preliminary Technical Data
DB31 – DB28
X 0 1 0 1 1/0 1/0 1/0 1/0 x 1/0 1/0
Don’t Cares
Table 8. 32-Bit Input Shift Register Contents Clear Code Function
LDAC Function
The outputs of all DACs may be updated simultaneously using the hardware /LDAC pin. Synchronous LDAC: The DAC registers are updated after new data is read in on the falling edge of the 32nd SCLK pulse. LDAC can be permanently low or pulsed as in Figure 1. Asynchronous LDAC: The outputs are not updated at the same time that the input registers are written to. When LDAC goes low, the DAC registers are updated with the contents of the input register.
The outputs of all DACs may be updated simultaneously using the /LDAC function, with the added functionality of selecting through software any number of DAC channels to synchronize. Writing to the DAC using command 110, the hardware /LDAC pin can be overwritten by setting the bits of the 8-bit /LDAC register (DB7-DB0) . SeeTable 9 for the /LDAC mode of operation. The default for each channel is “0” ie /LDAC pin works normally. Setting the bits to a “1” means the DAC channel will be updated regardless of the state of the /LDAC pin. This gives the added benefit of allowing any combination of channels to be synchronously updated. See Table 10 for contents of the Input Shift Register during the /LDAC overwrite mode of operation.
DB27 DB26 DB25 DB24 DB23 DB22 DB21 DB20 DB2-
DB19
COMMAND BITS (C2-C0) ADDRESS BITS (A3 – A0)
Don’t Cares
DB1 DB0
Clear Code Register (CR1­CR0)
Load DAC OVERWRITE
/LDACBITS (DB7­DB0)
0 1/0
1 x – Don’t Care
Table 9. LDAC Overwrite Definition
/LDAC PIN /LDAC Operation
Determined by /LDAC pin
DAC channels will update, overwriting the /LDAC pin
Rev.PrB | Page 20 of 22
Preliminary Technical Data
MSB LSB
AD5678
DB3
DB2 1 – DB2 8
x 0 1 1 0 x x x x x DacH DacG DacF DacE DacD DacC DacB DacA
Don’t Cares
DB26 DB25 DB24 DB23 DB22 DB21 DB2
7
COMMAND BITS (C2-C0) ADDRESS BITS (A3 – A0)
Don’t cares
DB8
DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
0
DB1 9
Don’t
Setting /LDAC bit to “1” overwrites /LDAC pin
Cares
Table 10. 32-Bit Input Shift Register Contents for /LDAC Overwrite Function
Power Supply Bypassing and Grounding
Inductance (ESI), e.g., common ceramic types of capacitors.
This 0.1 µF capacitor provides a low impedance path to ground When accuracy is important in a circuit it is helpful to carefully consider the power supply and ground return layout on the
for high frequencies caused by transient currents due to internal
logic switching. board. The printed circuit board containing the AD5678 should have separate analog and digital sections, each having its own area of the board. If the AD5678 is in a system where other devices require an AGND to DGND connection, the connection should be made at one point only. This ground point should be as close as possible to the AD5678.
The power supply line itself should have as large a trace as
possible to provide a low impedance path and reduce glitch
effects on the supply line. Clocks and other fast switching
digital signals should be shielded from other parts of the board
by digital ground. Avoid crossover of digital and analog signals
if possible. When traces cross on opposite sides of the board, The power supply to the AD5678 should be bypassed with 10 µF and 0.1 µF capacitors. The capacitors should be physically as close as possible to the device with the 0.1 µF capacitor ideally right up against the device. The 10 µF capacitors are the tantalum bead type. It is important that the 0.1 µF capacitor has low Effective Series Resistance (ESR) and Effective Series
ensure that they run at right angles to each other to reduce
feedthrough effects through the board. The best board layout
technique is the microstrip technique where the component
side of the board is dedicated to the ground plane only and the
signal traces are placed on the solder side. However, this is not
always possible with a two-layer board.
Rev. PrB| Page 21 of 22
AD5678
© 2005
PR05299-0-2/05(PrB)
OUTLINE DIMENSIONS
Preliminary Technical Data
0.201 (5.10)
0.193 (4.90)
0.177 (4.50)
0.006 (0.15)
0.002 (0.05)
SEATING
PLANE
14
0.169 (4.30)
1
PIN 1
0.0256 (0.65)
BSC
8
7
0.0118 (0.30)
0.0075 (0.19)
0.256 (6.50)
0.246 (6.25)
0.0433 (1.10) MAX
0.0079 (0.20)
0.0035 (0.090)
8° 0°
0.028 (0.70)
0.020 (0.50)
Figure 26. 14-Thin Shrink Small Outline Package [TSSOP]
(RU-14)
Dimensions shown in millimeters
0.201 (5.10)
0.193 (4.90)
16 9
0.177 (4.50)
0.006 (0.15)
0.002 (0.05)
SEATING
PLANE
0.169 (4.30)
1
PIN 1
0.0256 (0.65)
BSC
0.0118 (0.30)
0.0075 (0.19)
8
0.256 (6.50)
0.246 (6.25)
0.0433 (1.10) MAX
0.0079 (0.20)
0.0035 (0.090)
8° 0°
0.028 (0.70)
0.020 (0.50)
Figure 27. 16-Thin Shrink Small Outline Package [TSSOP]
(RU-16)
Dimensions shown in millimeters
ORDERING GUIDE
1 Thin Shrink Small Outline Package (TSSOP)
© 2003 Analog Devices, Inc. All rights reserved. Trademarks and registered
trademarks are the property of their respective companies. Printed in the U.S.A.
Model INL (LSB) Power-On-Reset Internal Reference Package
Option1
AD5678ARUZ-2 ±32 Zero 2.5V RU-16
Rev.PrB | Page 22 of 22
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