Tool/software:
Hello,
Question for below:
1) In the error amplifer, how to read the phase margin? I suppose it should go to -180, but it's not.
2) For the control loop, what's specfic in schematic? I suppose it should be the same as error amplifier.
3) For the control loop, why the margin is 20degree? If compared with -180degree, the margin should be much bigger.
Hello Pan,
below shows a good example on how to read phase margin, gain margin and Fco (BW).
1) from the slide that you showed, looks like the error amplifier is at ~135deg
2) The systems they shows is under dumped and it is unstable with poor compensations
3) for stable systems should be at least 45 deg or more
Thanks!
Tahar
Hi Liping,
The slide attached is for the control loop only which is what you typically measure near the FB pin of the device. That slide is showing Phase margin = 67.5° and Gain margin ~23dB. This tends to be measured above top FB/VSENSE resistor.
As far as the control loop, that typical involves any components that affect output regulation:
TPS54620 offer external compensation to alter stability through COMP pin.
Regards,
Eileen
