Rainbow Electronics MAX5302 User Manual

__________________General Description

The MAX5302 combines a low-power, voltage-output, 12-bit digital-to-analog converter (DAC) and a precision output amplifier in an 8-pin µMAX package. It operates from a single +5V supply, drawing less than 280µA of supply current.

The output amplifier’s inverting input is available to the user, allowing specific gain configurations, remote sensing, and high output current capability. This makes the MAX5302 ideal for a wide range of applications, including industrial process control. Other features include a software shutdown and power-on reset.

The serial interface is SPI™/QSPI™/MICROWIRE™ compatible. The DAC has a double-buffered input, organized as an input register followed by a DAC register. A 16-bit serial word loads data into the input register. The DAC register can be updated independently or simultaneously with the input register. All logic inputs are TTL/CMOSlogic compatible and buffered with Schmitt triggers to allow direct interfacing to optocouplers.

Applications

Industrial Process Control

Automatic Test Equipment

Digital Offset and Gain Adjustment

Motion Control

Remote Industrial Control

Microprocessor-Controlled Systems

Features

♦ 12-Bit DAC with Configurable Output Amplifier

♦ +5V Single-Supply Operation

♦ Low Supply Current: 0.28mA Normal Operation

2µA Shutdown Mode

♦ Available in 8-Pin µMAX

♦ Power-On Reset Clears DAC Output to Zero

♦ SPI/QSPI/MICROWIRE Compatible

♦ Schmitt-Trigger Digital Inputs for Direct

Optocoupler Interface

MAX5302

Low-Power, 12-Bit Voltage-Output DAC

with Serial Interface

________________________________________________________________ Maxim Integrated Products 1

MAX5302

OUT

DIN

SCLK

DAC

REF

DAC

INPUT

CONTROL

GND

16-BIT

SHIFT

Functional Diagram Pin Configuration

19-1559; Rev 0; 10/99

Ordering Information

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769.

SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corp.

8 µMAX

PIN-PACKAGETEMP. RANGE

0°C to +70°C

-40°C to +85°CMAX5302EUA

MAX5302CUA

PART

REF

DIN

SCLK

GND

OUT

MAX5302

µMAX

TOP VIEW

MAX5302

Low-Power, 12-Bit Voltage-Output DAC with Serial Interface

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 8, VDD= +5V ±10%, V

REF

= +2.5V, RL= 5kΩ, CL= 100pF, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical val-

ues are at T

= +25°C. Output buffer connected in unity-gain configuration.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

VDDto GND..............................................................-0.3V to +6V

REF, OUT, FB to GND ................................-0.3V to (V

+ 0.3V)

Digital Inputs to GND ...............................................-0.3V to +6V

Continuous Current into Any Pin.......................................±20mA

Continuous Power Dissipation (T

= +70°C)

8-Pin µMAX (derate 4.10mW/°C above +70°C) .........330mW

Operating Temperature Ranges

MAX5302CUA...................................................0°C to +70°C

MAX5302EUA ................................................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10sec) .............................+300°C

Code dependent, minimum at code 1554 hex

4.5V ≤ VDD≤ 5.5V

CONDITIONS

kΩ

14 20R

REF

Reference Input Resistance

- 1.4V

REF

Reference Input Range

µV/V

PSRR

Power-Supply Rejection Ratio

800

±4

Bits

12N

Resolution

ppm/°C1Gain-Error Tempco

LSBGEGain Error (Note 1) -0.3 ±3

ppm/°C6TCV

Offset-Error Tempco

LSBINLIntegral Nonlinearity (Note 1)

±0.3 ±8 mVV

Offset Error

UNITS

MIN TYP MAXSYMBOL

PARAMETER

REF

= 0.67Vp-p

kHz

650

Reference -3dB Bandwidth

Input code = all 0s, V

REF

= 3.6Vp-p at 1kHz

REF

= 1Vp-p at 25kHz, code = full scale

77SINAD

Signal-to-Noise Plus Distortion Ratio

dB-84Reference Feedthrough

2.4V

Input Voltage High

VIN= 0 or V

pF8C

Input Capacitance

µA0.001 ±0.5I

Input Leakage Current

V0.8V

Input Voltage Low

STATIC PERFORMANCE—ANALOG SECTION

DIGITAL INPUTS

REFERENCE INPUT

MULTIPLYING-MODE PERFORMANCE

Guaranteed monotonic LSB±1.0DNLDifferential Nonlinearity

MAX5302

Low-Power, 12-Bit Voltage-Output DAC

with Serial Interface

_______________________________________________________________________________________ 3

(Note 3)

CS = VDD, DIN = 100kHz

Rail-to-rail (Note 2)

To ±1/2LSB, V

STEP

= 2.5V

CONDITIONS

mA0.28 0.4I

Supply Current

V4.5 5.5V

Supply Voltage

nVs5Digital Feedthrough

µs20Start-Up Time

µA0.001 ±0.1Current into FB

V0 to V

Output Voltage Swing

µs14Output Settling Time

V/µs0.6SRVoltage Output Slew Rate

UNITSMIN TYP MAXSYMBOLPARAMETER

(Note 3) µA420Supply Current in Shutdown

µA0.001 ±0.5Reference Current in Shutdown

ns40t

SCLK Pulse Width High

ns100t

SCLK Clock Period

ns40t

CSS

CS Fall to SCLK Rise Setup Time

ns40t

DIN Setup Time

ns0t

CSH

SCLK Rise to CS Rise Hold Time

ns40t

SCLK Pulse Width Low

ns40t

CS1

CS Rise to SCLK Rise Hold Time

ns100t

CSW

CS Pulse Width High

ns40t

CS0

SCLK Rise to CS Fall Delay

ns0t

DIN Hold Time

Note 1: Guaranteed from code 11 to code 4095 in unity-gain configuration. Note 2: Accuracy is better than 1LSB for V

OUT

= 8mV to (V

- 100mV), guaranteed by a power-supply rejection test at the end

points.

Note 3: R

= ∞, digital inputs at GND or VDD.

DIGITAL INPUTSDYNAMIC PERFORMANCE

POWER SUPPLIES

TIMING CHARACTERISTICS (Figure 6)

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 8, VDD= +5V ±10%, V

REF

= +2.5V, RL= 5kΩ, CL= 100pF, TA= T

MIN

to T

MAX

, unless otherwise noted. Typical val-

ues are at T

= +25°C. Output buffer connected in unity-gain configuration.)

MAX5302

Low-Power, 12-Bit Voltage-Output DAC with Serial Interface

4 _______________________________________________________________________________________

-60 -20 20 60 100 140

MAX5302 toc04

POWER-DOWN SUPPLY CURRENT (µA)

POWER-DOWN SUPPLY CURRENT

vs. TEMPERATURE

TEMPERATURE (°C)

-100

0.5 1.6 3.8

OUTPUT FFT PLOT

-60

MAX5302 toc07

FREQUENCY (kHz)

2.7 4.9 6.0

-20

-40

-80

REF

= 3.6Vp-p CODE = FULL SCALE f

= 1kHz

SIGNAL AMPLITUDE (dB)

4.0 4.4 4.8 6.05.2 5.6

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX5302 toc05

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

400

350

500

450

300

250

150

100

200

-50

-90 1

100

TOTAL HARMONIC DISTORTION

PLUS NOISE vs. FREQUENCY

-85

MAX5302 toc06

FREQUENCY (kHz)

THD + NOISE (dB)

-70

-60

-55

-80

-75

-65

REF

= 2.5VDC + 1Vp-p SINE

CODE = FULL SCALE

2.49956

2.49960

2.49964

2.49968

2.49972

2.49976

2.49980

0.1k 1k 10k 1M100k

FULL-SCALE OUTPUT vs. LOAD

MAX5302 toc08

LOAD (Ω)

FULL-SCALE OUTPUT (V)

-100

0.5 1.6 3.8

REFERENCE FEEDTHROUGH

AT 1kHz

-60

MAX5302-09a/09b

FREQUENCY (kHz)

2.7 4.9 6.0

-20

-40

-80

OUTPUT FEEDTHROUGH

REFERENCE INPUT SIGNAL

SIGNAL AMPLITUDE (dB)

__________________________________________Typical Operating Characteristics

(VDD= +5V, RL= 5kΩ, CL= 100pF, TA = +25°C, unless otherwise noted.)

INL (LSB)

-0.5

0.4 1.2 2.0 2.8 3.6 REFERENCE VOLTAGE (V)

MAX5302 toc01

4.4

0.3

0.2

0.1

-0.1

-0.2

-0.3

-0.4

INTEGRAL NONLINEARITY

vs. REFERENCE VOLTAGE

-4

-8

-12

-16

-20 500k0

1M 1.5M

2M 2.5M 3M

MAX5302 toc02

RELATIVE OUTPUT (dB)

REFERENCE VOLTAGE INPUT

FREQUENCY RESPONSE

FREQUENCY (Hz)

400

380

360

340

320

300

280

260

240

220

200

-60 -20 20 60 100 140

MAX5302 toc03

SUPPLY CURRENT (µA)

SUPPLY CURRENT

vs. TEMPERATURE

TEMPERATURE (°C)

RL = ∞

MAX5302

Low-Power, 12-Bit Voltage-Output DAC

with Serial Interface

_______________________________________________________________________________________ 5

2µs/div

OUT

AC-COUPLED

10mV/div

CODE = 2048

DIGITAL FEEDTHROUGH (f

SCLK

= 100kHz)

MAX5302 toc11

SCLK

2V/div

CS = 5V

Typical Operating Characteristics (continued)

(VDD= +5V, RL= 5kΩ, CL= 100pF, TA = +25°C, unless otherwise noted.)

10µs/div

MAJOR-CARRY TRANSITION

MAX5302 toc10

OUT

AC-COUPLED

100mV/div

5V/div

10µs/div

DYNAMIC RESPONSE

MAX5302 toc12

OUT

1V/div

GND

GAIN = 2, SWITCHING FROM CODE 0 TO 4020

MAX5302

Low-Power, 12-Bit Voltage-Output DAC with Serial Interface

6 _______________________________________________________________________________________

Detailed Description

The MAX5302 contains a voltage-output digital-to-analog converter (DAC) that is easily addressed using a simple 3-wire serial interface. The IC includes a 16-bit shift register, and has a double-buffered input composed of an input register and a DAC register (see

Functional

Diagram). In addition to the voltage output, the amplifier’s

negative input is available to the user.

The DAC is an inverted R-2R ladder network that converts a digital input (12 data bits plus 1 sub-bit) into an equivalent analog output voltage in proportion to the applied reference voltage. Figure 1 shows a simplified circuit diagram of the DAC.

Reference Inputs

The reference input accepts positive DC and AC signals. The voltage at the reference input sets the full-scale output voltage for the DAC. The reference input voltage range is 0 to (VDD- 1.4V). The output voltage (V

OUT

) is represented by a digitally programmable voltage source, as expressed in the following equation:

OUT

= (V

REF

· NB / 4096) Gain

where NB is the numeric value of the DAC’s binary input code (0 to 4095), V

REF

is the reference voltage,

and Gain is the externally set voltage gain.

The impedance at the reference input is code dependent, ranging from a low value of 14kΩ when the DAC has an input code of 1554 hex, to a high value exceeding several gigaohms (leakage currents) with an input code of 0000 hex. Because the input impedance at the reference pin is code dependent, load regulation of the reference source is important.

In shutdown mode, the MAX5302’s REF input enters a high-impedance state with a typical input leakage current of 0.001µA.

The reference input capacitance is also code dependent and typically ranges from 15pF (with an input code of all 0s) to 50pF (at full scale).

The MAX873 +2.5V reference is recommended for the MAX5302.

Output Amplifier

The MAX5302’s DAC output is internally buffered by a precision amplifier with a typical slew rate of 0.6V/µs. Access to the output amplifier’s inverting input provides the user greater flexibility in output gain setting/signal conditioning (see the Applications Information section).

With a full-scale transition at the MAX5302 output, the typical settling time to ±1/2LSB is 14µs when loaded with 5kΩ in parallel with 100pF (loads less than 2kΩ degrade performance).

The amplifier’s output dynamic responses and settling performances are shown in the Typical Operating Char- acteristics.

Shutdown Mode

The MAX5302 features a software-programmable shutdown that reduces supply current to a typical value of 4µA. Writing 111X XXXX XXXX XXXX as the input control word puts the device in shutdown mode (Table 1).

In shutdown mode, the amplifier’s output and the reference input enter a high-impedance state. The serial interface remains active. Data in the input registers is retained in shutdown, allowing the MAX5302 to recall the output state prior to entering shutdown. Exit shutdown mode by either recalling the previous configuration or

OUT

SHOWN FOR ALL 1s ON DAC

MSB

2R 2R 2R 2R

RRR

REF

AGND

Figure 1. Simplified DAC Circuit Diagram

_____________________Pin Description

NAME FUNCTION

1 OUT DAC Output Voltage

Chip-Select Input. Active low.

3 DIN Serial-Data Input

4 SCLK Serial-Clock Input

8 V

Positive Power Supply

7 GND Ground

6 REF Reference Voltage Input

5 FB DAC Output Amplifier Feedback

MAX5302

Low-Power, 12-Bit Voltage-Output DAC

with Serial Interface

_______________________________________________________________________________________ 7

SCLK

DIN

I/O

MAX5302

MICROWIRE

PORT

Figure 2. Connections for MICROWIRE

DIN

SCLK

MOSI

SCK

I/O

SPI/QSPI

PORT

+5V

CPOL = 0, CPHA = 0

MAX5302

Figure 3. Connections for SPI/QSPI

Figure 4. Serial-Data Format

3 Control

Bits

12+1 Data Bits

D11.....................................D0, S0C2 C1 C0

Data Bits

MSB ................................LSB Sub-Bit

Control

Bits

16 Bits of Serial Data

MSB ..................................................................................LSB

Table 1. Serial-Interface Programming Commands

X = Don’t care

16-BIT SERIAL WORD

01 1

X0 0

X0 1

X1 0

11 1

No operation (NOP)

Load input register; DAC register immediately updated (also exit shutdown).

D11...............D0

MSB LSB

FUNCTION

Load input register; DAC register unchanged.

C2 C1 C0

Update DAC register from input register (also exit shutdown; recall previous state).

Shutdown

XXXXXXXXXXXX

12 bits of data

XXXXXXXXXXXX

by updating the DAC with new data. When powering up the device or bringing it out of shutdown, allow 20µs for the output to stabilize.

Serial-Interface Configurations

The MAX5302’s 3-wire serial interface is compatible with both MICROWIRE (Figure 2) and SPI/QSPI (Figure 3). The serial-input word consists of 3 control bits followed by 12+1 data bits (MSB first), as shown in Figure 4. The 3-bit control code determines the MAX5302’s response outlined in Table 1.

The MAX5302’s digital inputs are double buffered. Depending on the command issued through the serial interface, the input register can be loaded without affecting the DAC register, the DAC register can be loaded directly, or the DAC register can be updated from the input register (Table 1).

Serial-Interface Description

The MAX5302 requires 16 bits of serial data. Table 1 lists the serial-interface programming commands. For certain commands, the 12+1 data bits are “don’t cares.” Data is sent MSB first and can be sent in two 8-bit packets or one 16-bit word (CS must remain low until 16 bits are transferred). The serial data is composed of 3 control

MAX5302

Low-Power, 12-Bit Voltage-Output DAC with Serial Interface

8 _______________________________________________________________________________________

TO OTHER SERIAL DEVICES

MAX5302

DIN

SCLK

DIN

SCLK

DIN

SCLK

DIN

SCLK

CS1

CS2

CS3

MAX5302 MAX5302

Figure 7. Multiple MAX5302s Sharing Common DIN and SCLK Lines

SCLK

DIN

COMMAND

EXECUTED

C2 S0

D11

D10

D8 D5 D4 D3 D2 D1 D0D7 D6

Figure 5. Serial-Interface Timing Diagram

Figure 6. Detailed Serial-Interface Timing Diagram

SCLK

DIN

CSO

CSS

CSW

CS1

CSH

bits (C2, C1, C0), followed by the 12+1 data bits D11...D0, S0 (Figure 4). Set the sub-bit (S0) to zero. The 3-bit control code determines the register to be updated and the configuration when exiting shutdown.

Figures 5 and 6 show the serial-interface timing requirements. The chip-select (CS) pin must be low to enable the DAC’s serial interface. When CS is high, the interface control circuitry is disabled. CS must go low at least t

CSS

before the rising serial-clock (SCLK) edge to

properly clock in the first bit. When CS is low, data is clocked into the internal shift register through the serialdata input pin (DIN) on SCLK’s rising edge. The maximum guaranteed clock frequency is 10MHz. Data is latched into the MAX5302 input/DAC register on CS’s rising edge.

Figure 7 shows a method of connecting several MAX5302s. In this configuration, the clock and the data bus are common to all devices, and separate chip-select lines are used for each IC.

Applications Information

Unipolar Output

For a unipolar output, the output voltage and the reference input have the same polarity. Figure 8 shows the MAX5302 unipolar output circuit, which is also the typical operating circuit. Table 2 lists the unipolar output codes.

Figure 9 illustrates a Rail-to-Rail

output. This circuit shows the MAX5302 with the output amplifier configured with a closed-loop gain of +2 to provide a 0V to 5V fullscale range when a 2.5V reference is used.

Bipolar Output

The MAX5302 output can be configured for bipolar operation using Figure 10’s circuit according to the following equation:

OUT

= V

REF

[(2NB / 4096) - 1]

where NB is the numeric value of the DAC’s binary input code. Table 3 shows digital codes (offset binary) and the corresponding output voltage for Figure 10’s circuit.

Using an AC Reference

In applications where the reference has AC-signal components, the MAX5302 has multiplying capability within the reference input range specifications. Figure 11 shows a technique for applying a sine-wave signal to the reference input where the AC signal is offset before being applied to REF. The reference voltage must never be more negative than GND.

The MAX5302’s total harmonic distortion plus noise (THD+N) is typically less than -77dB (full-scale code), given a 1Vp-p signal swing and input frequencies up to 25kHz. The typical -3dB frequency is 650kHz, as shown in the Typical Operating Characteristics graphs.

MAX5302

Low-Power, 12-Bit Voltage-Output DAC

with Serial Interface

_______________________________________________________________________________________ 9

Table 2. Unipolar Code Table

ANALOG OUTPUT

1111 1111 1111 (0)

1000 0000 0001 (0)

DAC CONTENTS

MSB LSB

1000 0000 0000 (0)

0111 1111 1111 (0)

0000 0000 0000 (0)

0000 0000 0001 (0)

Note: ( ) are for sub-bit.

MAX5302

DAC

REF

OUT

GND

+5V

Figure 8. Unipolar Output Circuit

Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd.

REF

2048

 



4096

REF

4095

 



4096

2049

 



4096

 



2047

 



4096

 



4096

 



 



REF

 



 



MAX5302

Low-Power, 12-Bit Voltage-Output DAC with Serial Interface

10 ______________________________________________________________________________________

DAC

OUT

V+

+5V

V-

R1 = R2 = 10kΩ ±0.1%

REF

OUT

MAX5302

GND

Figure 10. Bipolar Output Circuit

Digitally Programmable Current Source

The circuit of Figure 12 places an NPN transistor (2N3904 or similar) within the op amp feedback loop to implement a digitally programmable, unidirectional current source. The output current is calculated with the following equation:

OUT

= (V

REF

/ R) (NB / 4096)

where NB is the numeric value of the DAC’s binary input code, and R is the sense resistor shown in Figure 12.

Power-Supply Considerations

On power-up, the input and DAC registers are cleared (set to zero code).

For rated MAX5302 performance, V

REF

must be at least

1.4V below VDD. Bypass VDDwith a 4.7µF capacitor in parallel with a 0.1µF capacitor to GND. Use short lead lengths and place the bypass capacitors as close to the supply pins as possible.

Grounding and Layout Considerations

Digital or AC transient signals on GND can create noise at the analog output. Connect GND to the highest-quality ground available.

Good PC board ground layout minimizes crosstalk between the DAC output, reference input, and digital input. Reduce crosstalk by keeping analog lines away from digital lines. Wire-wrapped boards are not recommended.

Table 3. Bipolar Code Table

MAX5302

DAC

REF

OUT

10k

GND

+5V

Figure 9. Unipolar Rail-to-Rail Output Circuit

ANALOG OUTPUT

1111 1111 1111 (0)

1000 0000 0001 (0)

DAC CONTENTS

MSB LSB

1000 0000 0000 (0) 0V

0111 1111 1111 (0)

0000 0000 0000 (0)

0000 0000 0001 (0)

Note: ( ) are for sub-bit.

2047





REF



2048





REF



2048



-V



REF



2048

2047



-V



REF



2048

 



2048

 



-V

REF REF

-V

 



 



 



 



MAX5302

Low-Power, 12-Bit Voltage-Output DAC

with Serial Interface

______________________________________________________________________________________ 11

Chip Information

TRANSISTOR COUNT: 3053

SUBSTRATE CONNECTED TO AGND

DAC

OUT

10k

26k

REF

GND

+5V

REFERENCE

INPUT

500mVp-p

MAX5302

MAX495

+5V

Figure 11. AC Reference Input Circuit

DAC

MAX5302

REF

OUT

2N3904

+5V

GND

Figure 12. Digitally Programmable Current Source

Low-Power, 12-Bit Voltage-Output DAC with Serial Interface

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Package Information

MAX5302

8LUMAXD.EPS

Rainbow Electronics MAX5302 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual