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TPS562201: poor load regulation

Mike Farley
Prodigy 735 points
Part Number: TPS562201
Other Parts Discussed in Thread: TPA6211A1, TPS562208

Assigned customer uses TPS562201 to supply class AB amp TPA6211A1.

7-11V input to TPS562201, configured for 5.4V out, into TPA6211A1 which drives a 2-3Vpk-pk max speech signal into a 6Ohm speaker ~0.5A rms load current).

TPS562201 Vout appears to have poor load regulation as there is a 1V pk-pk a.c signal appearing to modulate Vout at the sine wave low KHz test frequencies applied to the amplifier.

As per attached schematic, output capacitance is 3 x 10uF X5R ceramic + 1 x 33pF C0G ceramic, no compensation fitted.

Please review the schematic and advise - thank you,

MikeTPS562201 load regulation issue PDF.pdf

  • 0
    TI__Expert 4875 points
    Hi Mike,

    TPS562201is an eco mode part and it will get higher Vout at light load compared to heavy load condition. It is due to the high output ripple during light load skip mode. I am not sure whether the device loading current is small in your application. You could try to use TPS562208 which is a FCCM part and BOM to BOM to TPS562201. TPS562208 has a better load regulation at light load condition. Thanks!

    I am not familiar with the function of TPA6211A1. Could you explain the connection between the load regulation and the performance of the amplifier? What does it mean" there is a 1V pk-pk a.c signal appearing to modulate Vout at the sine wave low KHz test frequencies applied to the amplifier."

    Thanks!

    Best,
    Anthony
  • 0 in reply to Anthony Lang
    TI__Prodigy 735 points

    Hi Anthony,

    Understood that ripple will increase at light load, but to clarify, the 1V a.c. signal I'm referring to is appearing on top of the Vout of the TPS part, at the same frequency being used to drive the amplifier, so in response to changing load current (few mA up to 600mA peak) - and assumed to be unrelated to the skip operation so far.

    I assume we don't expect dips of approx 1V in Vout?

    What is the expected loop response time please? (I assume a few uS rather than up to a millisecond, if you consider a 1KHz tone in the amplifier)

    Many Thanks,
    Mike

  • 0 in reply to Mike Farley
    TI__Expert 4875 points
    Hi MIke,

    I think you are referring to output ripple, not load regulation, correct? I don't think the output ac ripple could be 1V and with a millisecond period. Could you share your waveform? Also, could you let me know how is the loading and input voltage is changing when you saw the issue. Maybe it is related to load transient and line transient. Thanks!

    Best,
    Anthony
  • 0 in reply to Anthony Lang
    TI__Prodigy 735 points
    Sorry if I've not described clearly enough Anthony...
    1. The TPS562201's load is the TPA6211A1 amplifier with a sine wave test signal driving a speaker.
    2. In this test case, the load presented to the TPS562201's output is a sine wave current waveform approx. equal to the current consumed in the speaker (up to 600mA peaks and 200mA rms, according to the customer).
    3. The customer finds that instead of a steady 5.4Vdc output, he sees a sinewave ripple on Vout of the TPS part with a frequency equal to that being applied to the amplifier input (the load current follows this amplifier test signal input).
    4. Because the output ripple is very large (around 1Vpk-pk) and at the amplifier test frequency, we can infer that the regulator is not regulating quickly enough to compensate for the change in load current -> hence the poor load regulation diagnosis.

    Q: why is the TPS562201's loop response seemly not fast enough to cope with comparatively low audio frequencies (0.3 - 8KHz)?
    And/Or - do you have another suggestion for the root cause? (in case you agree with the use case in the schematic)

    I will try to collect a waveform, but appreciate your comments meantime.

    Many Thanks,
    Mike
  • 0 in reply to Mike Farley
    TI__Expert 4875 points

    Hi Mike,

    I start to understand your case. What you saw is an variant load at TPS562201 (up to 600mA peaks and 200mA rms) and you saw a same low frequency output ripple which has a high peak to peak ac voltage. Is it correct? If this is the case, I think what you refer to is a poor load transient performance. For TPS562201, the load transient performance is very good due to its DCAP2 mode. I think there should be some other root cause for this. What is your input voltage when you saw this issue. You said the input could drop to 7V. I also would like to know how the input voltage change. If a waveform is measured, please include input voltage, output voltage and SW waveform for me. It is better for me to know what is exactly happened instead of just trying to guess and assume. Thanks!

    Best,

    Anthony

  • 0 in reply to Anthony Lang
    TI__Prodigy 735 points

    Hi Anthony,

    Sorry for the lack of comms, the issue is now sorted.

    It turned out that with the 5.4V output and 3.3uH inductors that actually were much lower value, there was not enough energy being store per cycle.

    The inductor is being changed to a 4.7uH as per the suggested typical in the datasheet.

    Thanks and Regards,

    Mike

  • 0 in reply to Mike Farley
    TI__Expert 4875 points
    Hi Mike,

    Thanks for your notice. Thanks!

    Best,
    Anthony