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TLV62569: bode plot measurement with PSM mode

Patrick Chen(TPE System & Application)
Expert 3430 points
Part Number: TLV62569

Hi Sir,

May I know if bode plot measurement with PSM mode is possible?

My customer using TLV62569 for a small current application and ask us to measure Gain margin and Phase margin.

we found that in PSM mode the Gain margin and phase margin could not pass(Gain<-10db,Phase >45degree), but in PWM mode it will pass.

Therefore, we would like to check with you:

1. May I know if bode plot measurement with PSM mode is possible?

2. Or we should make the TLV62569 enter the PWM mode to measure the Gain margin/Phase Margin as a reference for light load?

Thanks,

Patrick

  • 0
    TI__Expert 3465 points
    Hello Patrick,

    it's a pleasure to support you. I will go straight to your points:
    1. PSM bode plot measurements do not make much sense since this mode is supported by PFM (pulse frequency modulation), which is highly non linear. If you want to check the dynamic performances in PSM, you may check the stability in the time domain . You need to make load transient measurements from a load condition that implies PWM operation to another that forces the device in PFM operation (and vice-versa).
    2. PFM and PWM operations work thanks to different control topologies implemented in the same device, hence it's not meaningful to correlate their stability or dynamic performances.

    Anyway, PFM operation (or PSM) is meant to be very stable because since the inductor current is completely reset (for each cycles it reaches 0A like in DCM) the average behavior of the filer stage is of single pole type.