ADR430/ADR431/ADR433/ADR434/ADR435/ADR439

Rev. J | Page 20 of 24

PROGRAMMABLE DAC REFERENCE VOLTAGE

By employing a multichannel DAC, such as the AD7398,

quad, 12-bit voltage output DAC, one of its internal DACs

and an ADR43x voltage reference can be used as a common

configuration is shown in Figure 41.

DAC A

DAC B

DAC C

DAC D

ADR43x

AD7398

R1 ± 0.1%

R2

± 0.1%

Figure 41. Programmable DAC Reference

and the ratio of R1 and R2, given by

⎟

⎠

⎞

⎜

⎝

⎛

×

+

⎟

⎠

⎞

⎜

⎝

⎛ +

×

=

R1

R2

D

R1

R2

V

V

N

REF

REFX

2

1

1

(6)

where:

D is the decimal equivalent of the input code.

N is the number of bits.

R1, R2

Digital Code

R1 = R2

0000 0000 0000

R1 = R2

1000 0000 0000

R1 = R2

1111 1111 1111

R1 = 3R2

0000 0000 0000

R1 = 3R2

1000 0000 0000

R1 = 3R2

1111 1111 1111

PRECISION VOLTAGE REFERENCE FOR DATA

CONVERTERS

The ADR43x family has a number of features that make it ideal

for use with ADCs and DACs. The exceptional low noise, tight

temperature coefficient, and high accuracy characteristics make

the ADR43x ideal for low noise applications, such as cellular

base station applications.

Another example of an ADC for which the ADR431 is well

suited is the AD7701. Figure 42 shows the ADR431 used as

the precision reference for this converter. The AD7701 is a 16-bit

ADC with on-chip digital filtering intended for the measurement

of wide dynamic range and low frequency signals, such as those

representing chemical, physical, or biological processes. It contains

a charge-balancing Σ-Δ ADC, a calibration microcontroller

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

communications port.

SERIAL CLOCK

READ (TRANSMIT)

DATA READY

+5V

ANALOG

SUPPLY

SERIAL CLOCK

RANGES

SELECT

CALIBRATE

ANALOG

INPUT

ANALOG

GROUND

–5V

ANALOG

SUPPLY

SLEEP

MODE

DRDY

CS

SCLK

SDATA

CLKIN

CLKOUT

SC1

SC2

DGND

AGND

CAL

BP/UP

GND

ADR431

AD7701

0.1µF

0.1µF

0.1µF

0.1µF

10µF

0.1µF

10µF

0.1µF

2

6

4

Figure 42. Voltage Reference for the AD7701 16-Bit ADC