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TPA3251: Short mode protection question...

Peter Tseng
Genius 5555 points
Part Number: TPA3251

Dear Sirs,

While my customer did the short mode protection function of output , they found there is some different with datasheet.

The protection mode that customer use is CB3C and they found there are 2 kinds of test result that shown as below waveform.  

 

Ch1: OCP signal, Ch2: current waveform for OCP, CH3: input sine wave, CH4:TPA3251 output current

Result 1:

Result 2:

Note:

1. CH1 and CH2 are waveform by customer protection design

2. As waveform we can see, CH2 waveform will change related with different TPA3251 output current

3. TPA3251 output inductor is 44uH, and output cap is 1uF

4. input waveform is 60Hz sine wave

5. customer hope the output is always result 2.

Please help to advice:

1. What reason will cause the result 1 happen?

2. Is there any design modification suggest? 

Thanks.

  • 0
    TI__Mastermind 19080 points

    Hi Peter,

    I suppose it's in PBTL configuration so you get ~32A current limit.

    Are the two tests in the same hardware setup? The output current essentially depends on the input level. If you look at the input level on the two waveforms, when the "OC" event triggered, the input level are different. And the current has not reached the OC limit.

    In waveform 1 case, could you capture the waveform of OUTP/N, Spk_P or Spk_N, current?

    Also, could you explain how you did the short test?

    Regards,

    Sam

  • 0 in reply to Sam(MPAA) Zhang
    Genius 5555 points

    Hi Sam,

    1. Due to it is difficult to rework and the only one side output current can be measured. The measured output current is around 16A.

    2. Because customer application is use low frequency transformer as output device(such as attached file page1), not speaker, it is difficult to measure the output voltage and current of the secondary side of the transformer.

    3. As the output current waveform, it is indeed the transient current to touch the 32A current protection.

    4. Please help to advise if there is any method to suppress this transient current? 

    Please also refer to attached file that customer updated some test waveform in it.

    Thanks.

    TPA3251_application problem by short test(more waveform) .pptx

  • 0 in reply to Peter Tseng
    TI__Mastermind 19080 points

    Hi,

    As the turn ratio is a large number, during the short test, will the magnetic core get saturated and lead to the current transient?

    I also noticed that the output of TPA3251 has 3 levels, 0V/-20V/+24V. Could you explain this? For a normal switching device, the output level should swing between GND(0V) and PVDD(24V).

    Thanks!

    Regards,

    Sam

  • 0 in reply to Sam(MPAA) Zhang
    Expert 2035 points

    HI Sam

    Below figure is the customer block diagram,

    use the TPA3251 To be a current amp, to driver the transfomer primary side,

    and the sencond side will generator 5000 v, to apply in the DUT

    in the worse case, the DUT will short, or breakdown

    sometimes the TPA3251 into CC mode, and keep output

    sometimes the TPA3251 will disable,

    customer hope the TPA3251 keep CC mode, when the output is short stage

    please advise it ,thanks

  • 0 in reply to Chen Alex1
    TI__Mastermind 19080 points

    Hi Alex,

    Can you try to do the short on primary side of the transformer or even without the transformer? It can helps to identify if the problem has anything to do with the transformer.

    Regards,

    Sam

  • 0 in reply to Sam(MPAA) Zhang
    TI__Mastermind 34235 points

    No response in a week, the thread will be closed.