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ADR292ER

Low Noise Micropower Precision Voltage References

Analog Devices 

ADR290/ADR291/ADR292

VIN

2

ADR29x 6

VOUT

GND

1␮F

4

RLW

VIN

RLW

A1

+VOUT

SENSE

+VOUT

FORCE

RL

100k⍀

A1 = 1/2 OP295

Figure 35. Advantage of Kelvin Connection

Low Power, Low Voltage Reference For Data Converters

The ADR29x family has a number of features that makes it

ideally suited for use with A/D and D/A converters. The low

supply voltage required makes it possible to use the ADR29x

with today’s converters that run on 3 V supplies without having

to add a higher supply voltage for the reference. The low quies-

cent current (12 µA max) and low noise, tight temperature coef-

ficient, combined with the high accuracy of the ADR29x makes

it ideal for low power applications such as hand-held, battery

operated equipment.

One such ADC for which the ADR291 is well suited is the

AD7701. Figure 36 shows the ADR291 used as the reference

for this converter. The AD7701 is a 16-bit A/D converter with

on-chip digital filtering intended for the measurement of wide

dynamic range, low frequency signals such as those representing

chemical, physical or biological processes. It contains a charge

balancing (sigma-delta) ADC, calibration microcontroller with

on-chip static RAM, a clock oscillator and a serial communica-

tions port.

This entire circuit runs on ± 5 V supplies. The power dissipation

of the AD7701 is typically 25 mW and, when combined with

the power dissipation of the ADR291 (60 µW), the entire circuit

still consumes about 25 mW.

Voltage Regulator For Portable Equipment

The ADR29x family of references is ideal for providing a stable,

low cost and low power reference voltage in portable equipment

power supplies. Figure 37 shows how the ADR290/ADR291/

ADR292 can be used in a voltage regulator that not only has

low output noise (as compared to switch mode design) and low

power, but also a very fast recovery after current surges. Some

precautions should be taken in the selection of the output ca-

pacitors. Too high an ESR (Effective Series Resistance) could

endanger the stability of the circuit. A solid tantalum capacitor,

16 V or higher, and an aluminum electrolytic capacitor, 10 V or

higher, are recommended for C1 and C2, respectively. Also, the

path from the ground side of C1 and C2 to the ground side of

R1 should be kept as short as possible.

CHARGER

INPUT

0.1␮F

2

VIN

6V

+

LEAD-ACID

BATTERY

VOUT 6

ADR29x

TEMP 3

GND

4

R3

510k⍀

2

7

6

3

4 OP20

IRF9530

+5V, 100mA

R1 R2

402k⍀ 402k⍀

1% 1%

C1 +

68␮F

TANT

+ C2

1000␮F

ELECT

Figure 37. Voltage Regulator for Portable Equipment

+5V

ANALOG

SUPPLY

0.1␮F 10␮F

0.1␮F

RANGES

SELECT

VIN

VOUT

ADR291

GND

AVDD

VREF

DVDD

SLEEP

MODE

AD7701

BP/UP

DRDY

CS

SCLK

SDATA

CALIBRATE

ANALOG

INPUT

CAL

AIN

ANALOG

GROUND

–5V

ANALOG

SUPPLY 0.1␮F

0.1␮F

AGND

AVSS

10␮F

CLKIN

CLKOUT

SC1

SC2

DGND

DVSS

0.1␮F

DATA READY

READ (TRANSMIT)

SERIAL CLOCK

SERIAL CLOCK

0.1␮F

Figure 36. Low Power, Low Voltage Supply Reference for

the AD7701

–14–

REV. A

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