The INA117 is a monolithic difference amplifier with the unique ability to accept up to ±200V common-mode input signals while operating on standard ±15V power supplies. Because the gain of the INA117 is set at 1V/V, and because the output would saturate into the rails at about ±12V, the maximum specified differential input range is ±10V. The INA117 is available in three standard 8-pin packages: hermetic TO-99, plastic DIP, and the small surface-mount SOIC package, specified for the -40ºC to +85°C temperature range.
Similarly, the INA149 is a precision 36V unity-gain difference amplifier with a very high input common-mode voltage range (±275V). On standard ±15V power supplies, the maximum specified differential input range is ±13.5V. The INA149 is available in the SOIC-8 package with operation specified over the extended industrial temperature range of -40°C to +125°C.
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Since the common-mode input range is high (±200V INA117 and ±275V INA149), it makes sense that some designers would also like to use these part for differential inputs greater than ±10V and ±13.5V. Figure 1 shows the recommended circuit for the INA117. Adding resistors to the input may seem simpler, but there are some problems with that approach.