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ADR420(RevB) View Datasheet(PDF) - Analog Devices

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ADR420 Datasheet PDF : 16 Pages
First Prev 11 12 13 14 15 16
Table III. VREFX vs. R1 and R2
R1, R2
R1 = R2
R1 = R2
R1 = R2
R1 = 3R2
R1 = 3R2
R1 = 3R2
Digital Code
0000 0000 0000
1000 0000 0000
1111 1111 1111
0000 0000 0000
1000 0000 0000
1111 1111 1111
VREF
2 VREF
1.3 VREF
VREF
4 VREF
1.6 VREF
VREF
VREFA
DACA
VREFB
DACB
VOUTA
R1
؎0.1%
R2
؎0.1%
VREF
VIN ADR425
VOUTB
VOB = V REFX (DB)
ADR420/ADR421/ADR423/ADR425
+5V
ANALOG
SUPPLY 0.1F
10F
0.1F
VIN
VOUT
ADR42x
GND
RANGES
SELECT
CALIBRATE
ANALOG
INPUT
ANALOG
GROUND
0.1F
5V
ANALOG
SUPPLY
0.1F
10F
AD7701
AVDD
VREF
DVDD
SLEEP
MODE
DRDV
CS
SCLK
SDATA
BP/UP
CLKIN
CAL
AIN
AGND
CLKOUT
SC1
SC2
DGND
AVSS
DVSS
0.1F
DATA READY
READ (TRANSMIT)
SERIAL CLOCK
SERIAL CLOCK
0.1F
VREFC
DACC
VOUTC
VOC = V REFX (DC)
VREFD
DACD
AD7398
VOUTD
VOD = V REFX (DD)
Figure 11. Programmable DAC Reference
Precision Voltage Reference for Data Converters
The ADR42x family has a number of features that make it ideal
for use with A/D and D/A converters. The exceptional low noise,
tight temperature coefficient, and high accuracy characteristics
make the ADR42x ideal for low noise applications such as cellular
base station applications.
Another example of ADC for which the ADR421 is also well-suited
is the AD7701. Figure 12 shows the ADR421 used as the precision
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 and 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 communications port.
Figure 12. Voltage Reference for 16-Bit A/D Converter
AD7701
Precision Boosted Output Regulator
A precision voltage output with boosted current capability can
be realized with the circuit shown in Figure 13. In this circuit,
U2 forces VO to be equal to VREF by regulating the turn on of
N1, therefore, the load current will be furnished by VIN. In this
configuration, a 50 mA load is achievable at VIN of 5 V. Moder-
ate heat will be generated on the MOSFET and higher current
can be achieved with a replacement of the larger device. In
addition, for heavy capacitive load with step input, a buffer may
be added at the output to enhance the transient response.
N1
VIN
2 U1
VIN
6
VOUT
5
TRIM
GND
4 ADR421
5V
2N7002
V+
AD8601
VU2
VO
RL 25
Figure 13. Precision Boosted Output Regulator
REV. B
–15–
 

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