OP193 View Datasheet(PDF) - Analog Devices
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OP193 Datasheet PDF : 20 Pages
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Data Sheet
A MICROPOWER FALSE-GROUND GENERATOR
Some single-supply circuits work best when inputs are biased
above ground, typically at ½ of the supply voltage. In these
cases, a false ground can be created by using a voltage divider
buffered by an amplifier. One such circuit is shown in Figure 30.
This circuit generates a false-ground reference at ½ of the supply
voltage, while drawing only about 27 μA from a 5 V supply.
The circuit includes compensation to allow for a 1 μF bypass
capacitor at the false-ground output. The benefit of a large
capacitor is that not only does the false ground present a very
low dc resistance to the load, but its ac impedance is low as well.
The OP193 can both sink and source more than 5 mA, which
improves recovery time from transients in the load current.
5V OR 12V
10kΩ
0.022µF
240kΩ
240kΩ
7
2
OP193
3
+
4
1µF
100Ω
6
2.5V OR 6V
+
1µF
Figure 30. A Micropower False-Ground Generator
A BATTERY-POWERED VOLTAGE REFERENCE
The circuit of Figure 31 is a battery-powered voltage reference
that draws only 17 μA of supply current. At this level, two AA
alkaline cells can power this reference for more than 18 months.
At an output voltage of 1.23 V at 25°C, drift of the reference is
only 5.5 μV/°C over the industrial temperature range. Load
regulation is 85 μV/mA with line regulation at 120 μV/V.
Design of the reference is based on the Brokaw band gap core
technique. Scaling of Resistor R1 and Resistor R2 produces
unequal currents in Q1 and Q2. The resulting ΔVBE across R3
creates a temperature-proportional voltage (PTAT), which, in
turn, produces a larger temperature-proportional voltage across
R4 and R5, V1. The temperature coefficient of V1 cancels (first
order) the complementary to absolute temperature (CTAT)
coefficient of VBE1. When adjusted to 1.23 V at 25°C, output
voltage temperature coefficient is at a minimum. Band gap
references can have start-up problems. With no current in R1
and R2, the OP193 is beyond its positive input range limit and
has an undefined output state. Shorting Pin 5 (an offset adjust
pin) to ground forces the output high under these circumstances
and ensures reliable startup without significantly degrading the
OP193’s offset drift.
OP193/OP293
R1
240kΩ
C1
1000pF
R2
1.5MΩ
V+
(2.5V TO 36V)
2
7
OP193
6
5
3
4
VOUT
(1.23V @ 25°C)
Q2 1 MAT01AH
2
+
3 VBE2
–
7 Q1
6
+
5 VBE1
–
V1
–
R4
130kΩ
R5, 20kΩ
OUTPUT
ADJUST
R3
68kΩ
ΔVBE
+
Figure 31. A Battery-Powered Voltage Reference
A SINGLE-SUPPLY CURRENT MONITOR
Current monitoring essentially consists of amplifying the voltage
drop across a resistor placed in series with the current to be
measured. The difficulty is that only small voltage drops can be
tolerated, and with low precision op amps, this greatly limits the
overall resolution. The single-supply current monitor of Figure 32
has a resolution of 10 μA and is capable of monitoring 30 mA
of current. This range can be adjusted by changing the current
sense resistor, R1. When measuring total system current, it may
be necessary to include the supply current of the current monitor,
which bypasses the current sense resistor, in the final result.
This current can be measured and calibrated (together with the
residual offset) by adjustment of the offset trim potentiometer,
R2. This produces a deliberate temperature dependent offset.
However, the supply current of the OP193 is also proportional
to temperature, and the two effects tend to track. Voltage devel-
oped at the noninverting input and amplified by (1 + R4/R5)
appears at VOUT.
V+
+
TO CIRCUIT
UNDER TEST
–
ITEST
R1
1Ω
3
7
OP193
6
4
2
5
1
R2
100kΩ
VOUT =
100mV/mA(I TEST )
R4
9.9kΩ
R5
100Ω
R3
100kΩ
Figure 32. Single-Supply Current Monitor
Rev. D | Page 15 of 20
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