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TPS2553-1: Not switching off when slowly increase the load.

christopher2
Intellectual 515 points
Part Number: TPS2553-1
Other Parts Discussed in Thread: TPS53353

Circuit diagram is very typical.

3.5V Vin, 1uF input capacitance, 100nF on the output, Fault pulled up to Vout by 100k, EN pin via 100k to the Vin.

The situation is following.

Current treshold is set to 100mA. 230K resistor from Pin ILim to GND. Now I connect 100 Ohm variable resistor  to the output of TPS2553-1 and I slowly increase the load current. It should cut off the output when the overrcurrent is reached. But it does not. When I increase the load faster it switching off. But When I very slowly increasing the load by hand it is just limiting the current at 104mA, output voltage is reduced almost to 0, depend from the resistor setting, it can goes dow to 0 on full short. So it work but partially.

From my ubderstanding it should be switched off and latched after 8 ms of over-current. Or am I wrong?

  • 0
    TI__Expert 8980 points
    Hi, Christopher,

    Sorry for late reply because of vacation.

    Your understanding is correct. TPS2553-1 should be switched off and latched after 8ms of over-current.

    I can not quite understand your description:
    "But When I very slowly increasing the load by hand it is just limiting the current at 104mA, output voltage is reduced almost to 0, depend from the resistor setting, it can goes dow to 0 on full short. So it work but partially."
    When you increase load to limit threshold, Vout is 0V. I thinks the part is switched and latched off. Isn't it correct? What's your question?

    If you slowly increase the load and the part isn't switched off, it might because the load still not touch the limit threshold.

    Regards,
    Bob
  • 0 in reply to Bob Ma
    Intellectual 515 points

    For sure it was over the threshold point. I had short circuit at the output.

    "When you increase load to limit threshold, Vout is 0V. I thinks the part is switched and latched off. Isn't it correct? What's your question?"

    No it is not correct.  Thats the problem it was not latched off. It was contentiously limiting the current at value of 104mA.

    In the meantime I noted that if I supply the TPS2553-1 IC from DC supply  it works ok. The problem exist when it is supplied  from DC/DC noisy converter, the TPS53353. When I added between them a ferrite ring with three turns it works ok.

    It seems they are very sensible devices.

  • 0 in reply to christopher2
    TI__Expert 8980 points
    Hi, Chris,

    Yes, this device is sensible to input noise. If dc-dc noise is too high, fault signal deglitch time might be prolonged. It's my first time to know noise will also influence latch-off. Thank you for this information.

    Do you have any more question that I can help on?

    Regards,
    Bob
  • 0 in reply to Bob Ma
    Intellectual 515 points

    Hi Bob, the problem was solved so no more question. thanks.