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ADR439BR-REEL7 View Datasheet(PDF) - Analog Devices

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ADR439BR-REEL7 Datasheet PDF : 24 Pages
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ADR430/ADR431/ADR433/ADR434/ADR435/ADR439
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 VREFX for the rest of the DACs. The circuit
configuration is shown in Figure 41.
VREFA
DAC A
VREFB
DAC B
VOUTA R1 ± 0.1%
R2
± 0.1%
VREF
VIN ADR43x
VOUTB
VOB = VREFX (DB)
VREFC
DAC C
VOUTC
VOC = VREFX (DC)
VREFD
DAC D
VOUTD
VOD = VREFX (DD)
AD7398
Figure 41. Programmable DAC Reference
The relationship of VREFX to VREF depends on the digital code
and the ratio of R1 and R2, given by
VREFX
=
VREF
⎜⎝⎛1 +
×
⎜⎝⎛1
+
R2
R1
⎟⎠⎞
D
2N
×
R2
R1
⎟⎞
(6)
where:
D is the decimal equivalent of the input code.
N is the number of bits.
VREF is the applied external reference.
VREFX is the reference voltage for DAC A to DAC D.
Table 10. VREFX vs. R1 and R2
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
VREF
2 VREF
1.3 VREF
VREF
4 VREF
1.6 VREF
VREF
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.
+5V
ANALOG
SUPPLY 0.1µF
10µF
AD7701
0.1µF
2
VIN
VOUT 6
ADR431
GND
4
AVDD
VREF
DVDD
SLEEP
MODE
DRDY
CS
SCLK
SDATA
0.1µF
DATA READY
READ (TRANSMIT)
SERIAL CLOCK
SERIAL CLOCK
RANGES
SELECT
CALIBRATE
ANALOG
INPUT
ANALOG
GROUND
0.1µF
–5V
ANALOG
SUPPLY
0.1µF
10µF
BP/UP
CAL
AIN
AGND
AVSS
CLKIN
CLKOUT
SC1
SC2
DGND
DVSS
0.1µF
Figure 42. Voltage Reference for the AD7701 16-Bit ADC
Rev. J | Page 20 of 24
 

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