Other Parts Discussed in Thread: OPA690
Hi expert,
My customer use OPA695 and find some of them output abnormal when temperature increases. Please see schematic and waveforms in attached pdf.
Regards and thanks.
Jiandong
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I am surprised it works at all, you are trying to make a current source with a current feedback part. The total feedback Transimpedance (that sets stability) includes the transconductance of the FET, that may well vary over temperature - the pin equivalent OPA690 is a drop in alternate to try, not as as fast, but pretty good on slew rate.
Hi Michael,
Thanks for your reply.
1. Could you explain why current feedback part can't make a current source?
2. As you mentioned, feedback transimpedance varies with temperature causes unstable. Do you think if can make OPA695 stable by increasing the feedback resistors?
Regards and thanks.
Jiandong
Well if you force it, a CFA can probably do this - but to buy phase margin over the FET transconductance range and load (the FET Zo and load form a thevinin equivalent source Z to the feedback network) you would want to raise the feedback R until you are stable over temp - which might just bandlimit you back to where a part like the OPA690 is just as adequate. yes, make R4 about 750ohm and see if your situation improves.