Datasheet

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
programmable V
REFX
for the rest of the DACs. The circuit
configuration is shown in Figure 41.
V
REFA
DAC A
V
REFB
DAC B
V
REFC
DAC C
V
REFD
DAC D
V
OUTA
V
OUTB
V
OUTC
V
OUTD
V
OB
=V
REFX
(D
B
)
V
OC
=V
REFX
(D
C
)
V
OD
=V
REFX
(D
D
)
ADR43x
AD7398
V
IN
V
REF
R1 ± 0.1%
R2
± 0.1%
04500-012
Figure 41. Programmable DAC Reference
The relationship of V
REFX
to V
REF
depends on the digital code
and the ratio of R1 and R2, given by
⎟
⎠
⎞
⎜
⎝
⎛
×+
⎟
⎠
⎞
⎜
⎝
⎛
+×
=
R1
R2D
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.
V
REF
is the applied external reference.
V
REFX
is the reference voltage for DAC A to DAC D.
Table 10. V
REFX
vs. R1 and R2
R1, R2 Digital Code V
REF
R1 = R2 0000 0000 0000 2 V
REF
R1 = R2 1000 0000 0000 1.3 V
REF
R1 = R2 1111 1111 1111 V
REF
R1 = 3R2 0000 0000 0000 4 V
REF
R1 = 3R2 1000 0000 0000 1.6 V
REF
R1 = 3R2 1111 1111 1111 V
REF
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- ADC, a calibration microcontroller
with on-chip static RAM, a clock oscillator, and a serial
communications port.
SERIAL CLOCK
READ (TRANSMIT)
DATA READY
+5
V
A
NALO
G
SUPPLY
SERIAL CLOCK
RANGES
SELECT
CALIBRATE
ANALOG
INPUT
ANALOG
GROUND
–5V
ANALOG
SUPPLY
DV
DD
SLEEP
MODE
DRDY
CS
SCLK
SDATA
CLKIN
CLKOUT
SC1
SC2
DGND
DV
SS
AV
SS
AGND
A
IN
CAL
BP/UP
V
REF
AV
DD
V
IN
V
OUT
GND
ADR431
AD7701
0.1µF
0.1µF
0.1µF
0.1µF
10µF
0.1µF
10µF
0.1µF
2
6
4
04500-013
Figure 42. Voltage Reference for the AD7701 16-Bit ADC