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OPA2156: OPA2156, or THS4631, in feedback path of INA597 instead of BUF634A

Part Number: OPA2156
Other Parts Discussed in Thread: BUF634A, , INA597, THS4631, BUF602

The BUF634A has to high of voltage offset for my application.  The datasheet for INA597 shows a BUF634A in the feedback path to boost the current drive.  Could I replace this with OPA2156 or THS4631?

  • Morning Michael, 

    The easiest way to think about this imbedded boost stages is as if you were the INA597 IC designer and wanted to add a much higher output power IC stage. The issues become, 

    1. Its DC performance is corrected by the overall loop (so your concern is misplaced)

    2. Can I keep the overall loop stable with the added phase shift through this power stage? Here, that includes layout prop delay. 

    So, you don't need to worry about offset for inside the loop power boost, I assume you are talking about this figure, 

    You do need to worry about phase margin (add the load to be sure). 

    The BUF634A being a poor DC and AC accurate part is used often here as suitable to the inside the loop app. It is pretty fast, but there are faster parts with shorter prop delay - unity gain wise, look at the BUF602 if it has enough V_I swing.