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ADR290GRU-REEL View Datasheet(PDF) - Analog Devices

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ADR290GRU-REEL Datasheet PDF : 15 Pages
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ADR290/ADR291/ADR292
VIN
ADR29x
VOUT
1F
GND
RLW
VIN
+VOUT
SENSE
A1
100k
RLW
+VOUT
FORCE
RL
A1 = 1/2 OP295
Figure 6. Advantage of Kelvin Connection
Low Power, Low Voltage Reference For Data Converters
The ADR29x family has a number of features that makes it
ideally suited for use with A/D and D/A converters. The low
supply voltage required makes it possible to use the ADR290
and ADR291 with todays converters that run on 3 V supplies
without having to add a higher supply voltage for the reference.
The low quiescent current (12 µA max) and low noise, tight
temperature coefficient, combined with the high accuracy of
the ADR29x makes it ideal for low power applications such
as hand-held, battery operated equipment.
One such ADC for which the ADR291 is well suited is the
AD7701. Figure 7 shows the ADR291 used as the 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, 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 communica-
tions port.
This entire circuit runs on ± 5 V supplies. The power dissipation
of the AD7701 is typically 25 mW and, when combined with
the power dissipation of the ADR291 (60 µW), the entire circuit
still consumes about 25 mW.
Voltage Regulator For Portable Equipment
The ADR29x family of references is ideal for providing a stable,
low cost and low power reference voltage in portable equipment
power supplies. Figure 8 shows how the ADR290/ADR291/
ADR292 can be used in a voltage regulator that not only has
low output noise (as compared to switch mode design) and
low power, but also a very fast recovery after current surges.
Some precautions should be taken in the selection of the out-
put capacitors. Too high an ESR (Effective Series Resistance)
could endanger the stability of the circuit. A solid tantalum
capacitor, 16 V or higher, and an aluminum electrolytic capacitor,
10 V or higher, are recommended for C1 and C2, respectively.
Also, the path from the ground side of C1 and C2 to the ground
side of R1 should be kept as short as possible.
CHARGER
INPUT 0.1F
6V
+
LEAD-ACID
BATTERY
VIN
ADR29x
VOUT
TEMP
GND
R1
402k
1%
R3
510k
OP20
R2
402k
1%
IRF9530
5V, 100mA
C1 + + C2
68F
1000F
TANT
ELECT
Figure 8. Voltage Regulator for Portable Equipment
+5V
ANALOG
SUPPLY
0.1F 10F
0.1F
RANGES
SELECT
VIN
VOUT
ADR291
GND
AVDD
VREF
DVDD
SLEEP
MODE
DRDY
AD7701 CS
SCLK
BP/UP
SDATA
CALIBRATE
ANALOG
INPUT
CAL
AIN
ANALOG
GROUND
5V
ANALOG
SUPPLY 0.1F
0.1F
AGND
AVSS
10F
CLKIN
CLKOUT
SC1
SC2
DGND
DVSS
0.1F
DATA READY
READ (TRANSMIT)
SERIAL CLOCK
SERIAL CLOCK
0.1F
Figure 7. Low Power, Low Voltage Supply Reference for
the AD7701
–14–
REV. B
 

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