Datasheet LT1189 (Analog Devices) - 9

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