SBOS487B June 2009 – March 2020 PGA280
The input clamp protects the precision input amplifier from large voltages between the inputs that occur from a fast signal slew rate in the input. This clamp circuit pulls current from the input pins while active. Current flowing through the clamp can influence the signal source and cause long settling delays on passive signal filters. The current is limited by internal resistors of approximately 2.4 kΩ. Dynamic overload can result from the difference signal as well as the common-mode signal.
The input clamp turns on when the input signal slew rate is faster than the amplifier slew rate (see the specification) and larger than ±1V. Appropriate input filtering avoids the activation. However, transients from MUX switching, internal switches, and gain switching action cannot be filtered; therefore, to avoid these transients, activate the current buffer (BUF). The buffer isolates the signal input from the clamp, and therefore avoids the current pulse (see Figure 44).