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Original question:

THS4524 - Pin connection of unused opamp

THS4524: Unused Pin of THS4524

Sunil Dwivedi98
Prodigy 240 points
Part Number: THS4524
Other Parts Discussed in Thread: THS4552, THS4551

Out of 4, 1 module of THS4524 is not being used in my schematics. Power Supply is common to all 4 modules. 3 modules are used in diff to diff mode. For the not used one, both inputs are shorted together and connected to ground. There is no feedback resistor for 4th module.

whether such scheme can create problem with the other 3 module of THS4524 ? Functionally board works fine but whether in the noisy environment, 4th module can create any damage or problem ?

  • 0
    Guru 140200 points

    Hi Sunil,

    I wouldn't do that. I would add four 1k feedback resistors.

    Kai

  • 0 in reply to kai klaas69
    Prodigy 240 points

    Hi Kai,

    Thanks for the reply. Whether absence of feedback resistor can cause any issue to other 3 module of THS4524 ?

  • 0 in reply to Sunil Dwivedi98
    Guru 47535 points

    Kai is correct, you need to set up the unused channel with feedback R's and input R's to ground. The Vcm pin can be floated. The way you have it now would probably peg the outputs at full supply differential delta. Kind of an unknown operating point and while it might not impact the other 3 channels, it is not prudent. 

    This quad FDA is incidentally the only quad out there, you might consider the much improved upgrade (available as a dual) the THS4552. Much smaller packaging also. Or, if you only need 3 channels, a dual and a single THS4551.