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LM5069: Output off after long time running

Rocky Chen
Expert 8860 points
Part Number: LM5069

Hi

We are using LM5069-2 as a 24V input hot swap. Recently, it is found after running some hours, the 24V output of LM5069 circuit could be dropped off to 0V and then it will become re-started to 24V. Since the same 24V is also used for other boards. Every board has LM5069. And only this board meet this issue. We suspect if there is any over current or power limit. After check, it looks the current limit and power limit has enough margin and the load could not trip it. So, we wonder to know, for this phenomenon, is there any other event or clue we should check? 

Thank you!

-Rocky

  • 0
    TI__Guru** 105361 points

    Hi Rocky,

    Can you please share filled up design calculator.  

    Can you also capture test waveform of GATE,  Vout, timer voltage and input current during turn-off  by keeping oscilloscope in trigger mode on GATE high to low.

    Best regards,

    Rakesh

  • 0 in reply to Rakesh
    TI__Expert 8860 points

    Hi Rakesh

    The issue could be re-produced by raise ambient temperature with a Heat gun of 70°C. See below waveforms of 24V, Timer and Gate. The chip become down and the timer voltage seems not correct. The chip could not be re-actived by power down and power up. Keep the board powered off for a night. Then, the chip could be actived and re-start to work in room temp. But once heat it, the issue repeated again like above.

    However, so far, this phenomenon looks happened only on some chips. And for other chips, it does not happen this issue. So, it looks there is some spec is temperature sensitive. Such as: we do not see current sense reference spec over temperature range. Would you please help check if there is any characterization data? We hope to get some clue to find out this issue.

    The sch is here, the real load is within 300mA. The current limit is set at 1A. Power limit is set at 5W for start up power limit.

  • 0 in reply to Rocky Chen
    TI__Guru** 105361 points

    Hi Rocky,

    Thanks for the details.

    The current limit is set at 55mV/50mOhm= 1.1A (typ) and the typical circuit breaker trip point is at 105mV/50mOhm = 2.1A.

    Please refer Figure 13 in the datasheet for the current limit threshold variation with the temperature. It is pretty constant over the temperature.

    Few questions to debug..

    1. Can you zoom-in with 5ms/div scale to see what's happening. 2s/div is large..
    2. Do you expect pulsed current of >2.1A from the down stream ?
    3. Have you swapped parts having issue to a good working board and tested ?
    4. Is marking on LM5069 on all the parts same ?

    Best regards, Rakesh

  • 0 in reply to Rakesh
    TI__Expert 8860 points

    Hi Rakesh

    We did ABBA test, and the issue followed the chips. They were already sent to FA, so now we can not make a zoom in waveform.

    Actually, we do not know what happened from downstream in real environment. But the load is within 300mA. Do you think these chips are already functional failure? The mark information on top side is 62R5 SNBB and the other chip is 79CK SNBB.

    Thanks!

    -Rocky

  • 0 in reply to Rocky Chen
    TI__Guru** 105361 points

    Hi Rocky,

    OK. Replicating the issue on EVM on those chips would give us some insight.

    Can you loop me into that FA email. The FA team can track back based on the top marking and lot details.

    Best regards, Rakesh

  • 0 in reply to Rakesh
    TI__Guru** 105361 points

    Hi Rocky,

    As FA is under going..   Please close this thread. The FA team will update you the progress.

    Regards, Rakesh