ADR292FR Analog Devices Inc, ADR292FR Datasheet - Page 14

• Manufacturer Part Number: ADR292FR
• Manufacturer: Analog Devices Inc

Specifications of ADR292FR

• Fixed / Adjust / Prog: Precision
• Output Voltage (max): 4.096V
• Temperature Coefficient: 20ppm/°C
• Reference Voltage Accuracy (max): 0.1
• Line Regulation: 100ppm/V
• Load Regulation: 100ppm/mA
• Input Voltage (max): 18V
• Operating Temp Range: -40C to 125C
• Operating Temperature Classification: Automotive
• Mounting: Surface Mount
• Pin Count: 8
• Package Type: SOIC N
• Lead Free Status / Rohs Status: Not Compliant

ADR291/ADR292
APPLICATIONS INFORMATION
NEGATIVE PRECISION REFERENCE WITHOUT
PRECISION RESISTORS
In many current-output CMOS DAC applications, where the
output signal voltage must be of the same polarity as the reference
voltage, it is often necessary to reconfigure a current-switching
DAC into a voltage-switching DAC through the use of a 1.25 V
reference, an op amp, and a pair of resistors. Directly using a
current-switching DAC requires an additional operational am-
plifier at the output to reinvert the signal. A negative voltage
reference is then desirable from the point that an additional
operational amplifier is not required for either reinversion
(current-switching mode) or amplification (voltage-switching
mode) of the DAC output voltage. In general, any positive voltage
reference can be converted into a negative voltage reference
through the use of an operational amplifier and a pair of matched
resistors in an inverting configuration. The disadvantage to that
approach is that the largest single source of error in the circuit is
the relative matching of the resistors used.
The circuit illustrated in Figure 33 avoids the need for tightly
matched resistors with the use of an active integrator circuit. In this
circuit, the output of the voltage reference provides the input drive
for the integrator. To maintain circuit equilibrium, the integrator
adjusts its output to establish the proper relationship between the
reference’s V
desired can be chosen by simply substituting for the appropriate
reference IC. There is one caveat with this approach: although rail-
to-rail output amplifiers work best in the application, these
operational amplifiers require a finite amount (mV) of headroom
when required to provide any load current. The choice for the
circuit’s negative supply should take this issue into account.
Figure 33. A Negative Precision Voltage Reference Uses No Precision Resistors
ADR291/
ADR292
GND
V
4
2
IN
OUT
V
OUT
and GND. Thus, any negative output voltage
6
100kΩ
1kΩ
1µF
A1 = 1/2 OP291,
1/2 OP295
A1
1µF
+5V
–5V
100Ω
–V
REF
Rev. E | Page 14 of 20
PRECISION CURRENT SOURCE
In low power applications, there is often a need for a precision
current source that can operate on low supply voltages. As
shown in Figure 34, any one of the devices in the ADR291/
ADR292 family of references can be configured as a precision
current source. The circuit configuration illustrated is a floating
current source with a grounded load. The reference’s output
voltage is bootstrapped across R
current into the load. With this configuration, circuit precision
is maintained for load currents in the range from the reference’s
supply current, typically 12 μA to approximately 5 mA.
HIGH VOLTAGE FLOATING CURRENT SOURCE
The circuit shown in Figure 35 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.
ADR291/
ADR292
Figure 35. High Voltage Floating Current Source
GND
V
2
4
IN
ADR291/
ADR292
Figure 34. A Precision Current Source
GND
V
2
4
IN
V
OUT
6
OP90
1µF
SET
ADJUST
, which sets the output
+V
I
SY
S
R
L
I
OUT
–V
R1
P1
2N3904
E231
SILICONIX
S
2.10kΩ
R
SET