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ADR291/ADR292
APPLICATIONS INFORMATION
HIGH VOLTAGE FLOATING CURRENT SOURCE
The circuit shown in Figure 33 can be used to generate a
floating current source with minimal self-heating. This
particular configuration operates on high supply voltages
determined by the breakdown voltage of the N-channel JFET.
+V S
E231
SILICONIX
2
V IN
LOW POWER, LOW VOLTAGE REFERENCE FOR
DATA CONVERTERS
The ADR291/ADR292 family has a number of features that
makes it ideally suited for use with analog-to-digital and digital-
to-analog converters. Because of its low supply voltage, the
ADR291 can be used with converters that run on 3 V supplies
without having to add a higher supply voltage for the reference.
The low quiescent current (12 μA maximum) and low noise,
tight temperature coefficient, combined with the high accuracy
of the ADR291/ADR292, make it ideal for low power applica-
tions such as handheld, battery-operated equipment.
ADR291/
ADR292
GND
4
OP90
2N3904
2.10k ?
One such ADC for which the ADR291 is well suited is the
AD7701 . Figure 35 shows the ADR291 used as the reference
for this converter. The AD7701 is a 16-bit ADC with on-chip
digital filtering intended for the measurement of wide dynamic
range, low frequency signals such as those representing chemical,
–V S
Figure 33. High Voltage Floating Current Source
KELVIN CONNECTIONS
In many portable instrumentation applications, the PC board
area is directly related to cost; therefore, circuit interconnects
are reduced to a minimal width. These narrow lines can cause
large voltage drops if the voltage reference is required to provide
load currents to various functions. In fact, circuit interconnects
physical, or biological processes. It contains a charge balancing
(Σ-Δ) ADC, calibration microcontroller with on-chip static
RAM, a clock oscillator, and a serial communications 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.
+5V
ANALOG
can exhibit a typical line resistance of 0.45 mΩ/square (1 oz. Cu,
for example). Force and sense connections, also referred to as
SUPPLY
0.1μF
10μF
AV DD
Kelvin connections, offer a convenient method of eliminating
the effects of voltage drops in circuit wires. Load currents flowing
through wiring resistance produce an error (V ERROR = R × I L ) at
0.1μF
V IN
V OUT
ADR291
V REF
DV DD
SLEEP
MODE
0.1μF
the load. However, the Kelvin connection shown in Figure 34
overcomes the problem by including the wiring resistance
within the forcing loop of the op amp. Since the op amp senses
the load voltage, the op amp loop control forces the output to
RANGES
SELECT
GND
AD7701 CS
BP/UP SDATA
DRDY
SCLK
DATA READY
READ (TRANSMIT)
SERIAL CLOCK
SERIAL CLOCK
compensate for the wiring error producing the correct voltage
at the load.
CALIBRATE
ANALOG
INPUT
CAL
A IN
CLKIN
CLKOUT
V IN
2
ADR291/
ADR292
V OUT 6
R LW
V IN
A1
R LW
+V OUT
SENSE
+V OUT
FORCE
R L
ANALOG
GROUND
–5V
ANALOG
SUPPLY
0.1μF
0.1μF
10μF
AGND
AV SS
SC1
SC2
DGND
DV SS
0.1μF
GND
4
1μF
100k ?
A1 = 1/2 OP295
Figure 35. Low Power, Low Voltage Supply Reference for the AD7701
Figure 34. Advantage of Kelvin Connection
Rev. F | Page 14 of 20
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ADR292 制造商:AD 制造商全称:Analog Devices 功能描述:Low Noise Micropower Precision Voltage References
ADR292ER 制造商:Analog Devices 功能描述:V-Ref Precision 4.096V 5mA 8-Pin SOIC N Tube 制造商:Analog Devices 功能描述:IC VOLT REF
ADR292ER-REEL 制造商:Analog Devices 功能描述:V-Ref Precision 4.096V 5mA 8-Pin SOIC N T/R
ADR292ER-REEL7 制造商:AD 制造商全称:Analog Devices 功能描述:Low Noise Micropower Precision Voltage References
ADR292ER-RELL 制造商:AD 制造商全称:Analog Devices 功能描述:Low Noise Micropower Precision Voltage References
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