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LM5176-Q1: Softstart Abnormal Issue

Lanxi Li
Expert 7555 points

Part Number: LM5176-Q1
Other Parts Discussed in Thread: LM5176

Tool/software:

Hello team,

My customer use LM5176 in their traction system at last, they can recurrence the softstart issue when doing the power on/off test.

As you can see, CH1-VIN, CH2-BBSW (Control Vin ON/OFF switching) CH3-EN, CH4-BB (buck-boost's out);

When VIN power on, the EN is pulled high immediately, but the Out is delayed 740ms which is abnormal.

They are testing more as below: CH1-FB, CH2-VIN, CH3-SS, CH4-OUT.

The SS pin is delayed 677ms to charge the cap at SS pin. 

Based on the test, please help check the root cause SS pin is delayed? Let me know if you need any more info?

Please help explain the SS pin working principle in LM5176?

Thank you.

Best regards,

Lanxi

  • 0
    TI__Mastermind 35900 points

    Hi Lanxi,

    Thanks for using the e2e forum.

    There are delays between turn-on of the EN pin and the SS pin to start ramping up, but this delay is normally in the range of 100us-500us.
    A delay of 700ms is indeed abnormally long, so there must be something, that keeps the device in shutdown mode for a longer time.

    Could customer measure the VCC voltage well?
    A fully ramped up VCC voltage is one of the start-up conditions for the softstart.

    Thanks and best regards,
    Niklas