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Original question:

TPS54335A: About light load operation

TPS54335A: About light load operation unregular

Wentao Zeng
Prodigy 590 points
Part Number: TPS54335A

Hi Team

My customer has faced one question.

CH1 is SW waveform,

CH2 is COMP voltage，

CH3 is in current waveform

 Vin=12V, Vout=1V to 5V.

Actually we use external Amplfier to to measure Current and Volatge and go back to COM to build Closed loop.

This is for battery testing equipment and need constant Volatge /constant Current (CC/CV control).

Now we face at light load condition. The Inductance current is ship, it also is normaly.

But we found it is not reguar, Maybe there has two continues PWM and next time has three PWM,or onely one PWM.

It is means that it is unstable? Normally it should has one regular PWM even enter into light load mode.

Or maybe noise come from COM pin that result in unregular  PWM?

Could you tell me the reason.

 

  • 0
    TI__Genius 10070 points

    Hi Wentao,

    1. Which mode dose the device work at when you tested this waveform? Current loop or voltage loop? Dose it have the same waveform in CC and CV?

    2. From the waveform, the loop seems to be unstable, you can test the waveform with 2A load to see whether it works well. If it is possible, you can test the bode plot and load transient to check the stability of loop.

    3. If it is convenient, please share the schematic.

  • 0 in reply to Shawn Nie
    TI__Prodigy 590 points
    We have test large current ,the waveform is good.
    Why there has two or three PWM somethimes ?
  • 0 in reply to Wentao Zeng
    TI__Genius 10070 points
    Hi Wentao,
    The fsw is 200kHz, from the waveform, it is correct, the device will skip the pulse when the peak switch current is lower
    than 0.5 A (typical), you can see the datasheet 7.2.3.
    Is the output current correct when you test this waveform?