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AD549LH amplifier and Pin 8

Question asked by jchan5 on May 24, 2018
Latest reply on Jun 1, 2018 by ARoxas

I'm attempting to rebuild a circuit, a transimpedance amplifier circuit for a silicon photomultiplier. The amplifier uses the AD549LH op-amp, and I'm in the process of 'rewriting' the circuit as there is no schematic to reference the circuit off of. Think of this old circuit as just an old brown board with no ground plane with everything connected to wires and the new circuit to be on a nice, shiny PCB board. The issue that I'm facing is with pin 8, the guard pin connected to the case. On the original circuit, it was not connected to anything, not to ground or anything. Normally, I'd just leave it unconnected, but when I looked at the datasheet of the amplifier, I saw that in some circuits that pin 8 was connected to something, whether it be ground or a resistor to ground. Given that, how should I use pin 8 in my circuit? 

 

Attached is a rough circuit of what I think the current circuit is based on measuring where the wires attach to and such. 

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