REV. B

ADR290/ADR291/ADR292

–14–

A1

1 F

100k

GND

ADR29x

SENSE

A1 = 1/2 OP295

FORCE

Figure 6. 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 ADR290

and ADR291 with today’s converters that run on 3 V supplies

without having to add a higher supply voltage for the reference.

The low quiescent current (12

µA max) and low noise, tight

temperature coefficient, 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 7 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.

BP/

UP

CAL

AGND

SLEEP

MODE

DRDY

SCLK

CS

SDATA

CLKIN

CLKOUT

SC1

SC2

DGND

0.1 F

DATA READY

READ (TRANSMIT)

SERIAL CLOCK

SERIAL CLOCK

0.1 F

10 F

0.1 F

–5V

ANALOG

SUPPLY

ANALOG

GROUND

ANALOG

INPUT

CALIBRATE

RANGES

SELECT

0.1 F

ADR291

0.1 F

GND

+5V

ANALOG

SUPPLY

10 F

0.1 F

AD7701

Figure 7. Low Power, Low Voltage Supply Reference for

the AD7701

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 8 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 out-

put capacitors. 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.

ADR29x

GND

0.1 F

LEAD-ACID

BATTERY

+

6V

CHARGER

INPUT

R1

402k

1%

R2

402k

1%

+ C2

1000 F

ELECT

C1

68 F

TANT

+

5V, 100mA

IRF9530

R3

510k

OP20

TEMP

Figure 8. Voltage Regulator for Portable Equipment