I have a customer who wants to buffer the FB loop of the TPS54623. The reason is to reduce current consumption on a highly sensitive / accurate current reading. Would adding in a buffer like the OPA189 create any issues with phase margin? This opamp (I think) has a small enough phase shift at low frequencies that the loop phase shift shouldn't go near 180 degrees. Can you confirm if there would be any issues here?
The gain for the regulator feedback loop is about 20 or about 26 dB. There is no GBW plot for the regulator amplifier but I’d guess no more than 50 kHz or so?
The OPA189 is being run as a buffer, at 0 dB the phase shift is about -10 to -15 degrees from what I can see from the open-loop plot. I think it will be OK unless the TPS54623 is right on the edge of about -170 degrees of phase shift.