LT1189 Просмотр технического описания (PDF) - Linear Technology
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LT1189 Datasheet PDF : 12 Pages
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LT1189
APPLICATI S I FOR ATIO
Instrumentation Amplifier Rejects High Voltage
Instrumentation amplifiers are often used to process
slowly varying outputs from transducers. With the LT1189
it is easy to make an instrumentation amplifier that can
respond to rapidly varying signals. Attenuation resistors
in front of the LT1189 allow very large common-mode
signals to be rejected while maintaining good frequency
response. The input common-mode and differential-mode
signals are reduced by 100:1, while the closed-loop gain
is set to be 100, thereby maintaining unity-gain input to
output. The unique topology allows for frequency re-
sponse boost by adding 150pF to pin 8 as shown.
3.5MHz Instrumentation Amplifier Rejects 120VP-P
VIN
VCM
120VP-P
10k*
10k*
* 0.1% RESISTORS
WORST CASE CMRR = 48dB
100*
100*
5V
2+
7
1 REF
6
3 – LT1189
8
FB 4
– 5V
10k
150pF 100Ω
LT1189 • AI03
Output of Instrumentation Amplifier with 1MHz Square Wave
Riding on 120VP-P at the Input
High Voltage Instrumentation Amplifier Response
20
0 DIFFERENTIAL-MODE RESPONSE
–20
COMMON-MODE RESPONSE
– 40
– 60
100k
1M
10M
FREQUENCY (Hz)
100M
LT1189 • AI05
Operating with Low Closed-Loop Gain
The LT1189 has been optimized for closed-loop gains of
10 or greater. The amplifier can be operated at much lower
closed-loop gains with the aid of a capacitor CFB across
the feedback resistor, (feedback zero). This capacitor
lowers the closed-loop 3dB bandwidth. The bandwidth
cannot be made arbitrarily low because CFB is a short at
high frequency and the amplifier will appear configured
unity-gain. As an approximate guideline, make BW × AVCL
= 200MHz. This expression expands to:
A VCL
2π(RFB )(C FB )
=
200MHz
or:
C FB
=
A VCL
(200MHz)(2π)(RFB )
The effect of the feedback zero on the transient and
frequency response is shown for AV = 4.
LT1189 • AI04
9
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