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TPS54425 OCP latching

Jose Garcia Navarro
Prodigy 40 points
Other Parts Discussed in Thread: TPS54425, TPS54427

Hi,

We are use TPS54425 to convert 12V input to 5.1V output. 3-4A max.

 

Schema is equal to TPS54425 data sheet, except: R1=22K1, R2=3k9, L1=3,3uH.

In data sheet, OCP (Overcurrent protection) and protections UVLO, UV, LO are no latching.

"EN" is permanently connected to Vin (12V).

Problem:

  • if a short circuit and over current Vout is disconnected permanently until deactivated and active again
  • if there is a 2200uF capacitor in parallel with Vin or Vin rises slowly with EN permanently connected to Vin, Vout = 0V. No output voltage

Regards,

Jose Garcia.

  • 0
    TI__Guru**** 191445 points

    I do not really understand your question.  Can you restate it?  If you can provide waveforms that demonstrate your concern that will help.

  • 0 in reply to JohnTucker
    Prodigy 40 points

    Dear John,

    ok,

    When a short circuit at the output ...

    the output remains permanently to 0 volts

    Does not resume operation until the DCDC do the following steps:

     1. - "EN" = 0V.
      2. - "EN" = 12V.

     

    No waveforms because there isn't output voltage.

     

    regards,

    Jose Garcia

     

  • 0 in reply to Jose Garcia Navarro
    TI__Mastermind 35165 points

    Hi Jose,

    The OCP and UVP sections can be misleading. The OCP section itself is non latching. But, if during the short circuit the UVP is tripped for greater than 250 us, then the part will latch off the two internal FETs until EN is toggled. The latching is described in the Over/Under Voltage Protection section.

    Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 40 points

    Dear Anthony,

     

    ok. I've checked in the data sheet, I understand.

    in practice, we found that releases easily for any small overhead.
    We believe that is not normal and there may be some unknown problem.

    The problem is that permanent disconnection is very dangerous because the system loses power and I can not reset it because I put "ON" to 0 (then VREG5 = 0V, no supply for uC, if I connect to VREG5 ) and then to 1 ..

    In our case this circuit feeds the electronics of an aircraft radio control of UAV / FPV.

    If power is disconnected for any small mistake and not restored the plane crashes.

    I think the TPS54425 is not suitable due to UV disconnect latch.
    In our case, there may be temporary overloads due to consumption of the servos.
    It is preferable to heat the DCDC.

    I will continue testing

    If you need more information I can send photos PCB, waves, etc.

    Thank you very much for your quick response

     
    Regards,

    Jose Garcia

    www.dmd.es

  • 0 in reply to Jose Garcia Navarro
    TI__Mastermind 35165 points

    Hi Jose,

    The TPS54425 will only latch if the over current brings the output voltage to lower than 65% the target output voltage. So it does not latch during all over current operations.

    How about the TPS54427 instead? This a similar part and does not have the latching UV protection.

    Regards,
    Anthony 

  • 0 in reply to Anthony F
    Prodigy 40 points

    Hi anthony,

     

    Ok. I Test TPS54427.

     

    Thanks,

    Jose Garcia