INA148 Datasheet, PDF (9/16 Pages) Burr-Brown (TI) – ±200V Common-Mode Voltage DIFFERENCE AMPLIFIER

THE GAIN EQUATION
An internal on-chip resistor network sets the overall differ-
ential gain of the INA148 to precisely 1V/V. It’s output is
accordance with the equation:
V_OUT = (V_I+N – V_I–N ) + V_REF
(1)
COMMON-MODE RANGE
The 20:1 input resistor ratio of the INA148 provides an input
common-mode range that extends well beyond its power
supply rails.
The exact input voltage range depends on the amplifier’s
power-supply voltage and the voltage applied to the Ref
terminal (pin 1). Typical input voltage ranges at different
power supply voltages can be found in the applications
circuits section.
OFFSET TRIM
The INA148 is laser-trimmed for low offset voltage and
drift. Most applications will require no external offset ad-
justment.
Since a voltage applied to the reference (Ref) pin (pin 1) will
be summed directly into the amplifier’s output signal, this
technique can be used to null the amplifier’s input offset
voltage. Figure 2 shows an optional circuit for trimming the
offset voltage.
To maintain high common-mode rejection (CMR), the source
impedance of any signal applied to the Ref terminal should
be very low (≤5Ω).
A source impedance of only 10Ω at the Ref pin will reduce
the INA148’s CMR to approximately 74dB. High CMR can
be restored if a resistor is added in series with the amplifier’s
positive input terminal (pin 3). This resistor should be 19
times the source impedance that drives the Ref pin. For
example, if the Ref pin sees a source impedance of 10Ω, a
resistor of 190Ω should be added in series with pin 3.
+V_S
7
V_I–N
2 ^1MΩ
50kΩ
50kΩ
V_O = (V_I+N – V_I–N) + V_REF
2.7778kΩ
6
A1
V_O
190Ω
1MΩ
V_I+N
3
52.6316kΩ
4
–V_S
±15mV Offset
Trim Range, RTI
V_REF 1
10Ω
INA148
10kΩ
+15V
10kΩ
–15V
FIGURE 2. Optional Offset Trim Voltage.
+15V
7
V_I–N
2 ^1MΩ
50kΩ
A1
50kΩ
2.7778kΩ
V_O = (V_I+N – V_I–N) + V_REF
6
V_O
1MΩ
V_I+N
3
52.6316kΩ
4
V_REF 1
INA148
–15V
±15mV Offset
Trim Range, RTI
OPA237
100kΩ
+15V
100kΩ
100Ω _–15V
FIGURE 3. Preferred Offset Trim Circuit.
9
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INA148