ADR421ARMZ datasheet(20/24 Pages) AD

20 / 24 page

ADR420/ADR421/ADR423/ADR425

Rev. I | Page 20 of 24

PRECISION VOLTAGE REFERENCE FOR DATA

CONVERTERS

PRECISION BOOSTED OUTPUT REGULATOR

A precision voltage output with boosted current capability

can be realized with the circuit shown in Figure 49. In this

circuit, U2 forces VOUT to be equal to VREF by regulating the turn

on of N1. Therefore, the load current is furnished by VIN. In

this configuration, a 50 mA load is achievable at VIN of 5 V.

Moderate heat is generated on the MOSFET, and higher current

can be achieved by replacing the larger device. In addition, for

a heavy capacitive load with step input, a buffer may be added

at the output to enhance the transient response.

The ADR42x family has a number of features that make it ideal

for use with ADCs and DACs. The exceptionally low noise,

tight temperature coefficient, and high accuracy characteristics

make the ADR42x ideal for low noise applications such as

cellular base station applications.

AD7701 is an example of an ADC that is well suited for the

ADR42x. The ADR421 is used as the precision reference for

the converter in Figure 48. The AD7701 is a 16-bit ADC with

on-chip digital filtering intended for measuring wide dynamic

range and low frequency signals, such as those representing

chemical, physical, or biological processes. It contains a charge-

balancing (Σ-Δ) ADC, calibration microcontroller with on-chip

static RAM, clock oscillator, and serial communications port.

VIN

VOUT

25Ω

AD8601

2N7002

V+

V–

–

ADR421

VIN

VOUT

TRIM

GND

AD7701

ADR420/

ADR421/

ADR423/

ADR425

VIN

AVDD

DVDD

SLEEP

MODE

DRDY

SCLK

SDATA

DATA READY

READ (TRANSMIT)

SERIAL CLOCK

CLKIN

CLKOUT

SC1

SC2

DGND

DVSS

VREF

BP/UP

CAL

AIN

AGND

AVSS

0.1µF

10µF

+5V

ANALOG

SUPPLY

RANGES

SELECT

CALIBRATE

ANALOG

INPUT

ANALOG

GROUND

–5V

ANALOG

SUPPLY

GND

VOUT

0.1µF

10µF

Figure 49. Precision Boosted Output Regulator

Figure 48. Voltage Reference for 16-Bit ADC AD7701

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