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LM25011: Encountering start-up issues

Fabio Gou
Intellectual 2810 points
Part Number: LM25011

The customer encountered start-up failure nearly 5% when there is a weak 1.4V in the output. (Which is leaked by the communication port TX.)

If there is no that weak 1.4V in the output, there is no any issues.

The customer have done AB/BA test. They found this issue follow the chip.

Yellow is the Output voltage.

Purple is the SW.

Green is the PG.

What is the potential reason for the 5% failure rate?

  • 0
    TI__Mastermind 28660 points

    Hello Fabio,

    the A/B swap test can mean you are sorting on spec limit edges, does not mean there is a specific failure of the device.

    please fill out design calculator with your specification and share so I can check your design again spec.  Also, I noted the Css is 100nF, is there a reason for this?  Does the issue occur on restart?  suggest rechecking issue with small SS cap, say 22nF.  

    Hope this helps.

    David.

  • 0 in reply to David Baba
    TI__Intellectual 2810 points

    Blue：BST(Pin10) to SW(Pin9) voltage

    Yellow：SS(Pin4) to GND

    Green：SW(Pin9) to GND

    Purple：Vout(3.3V) to GND

    The customer found the BST-SW voltage is only 5V-0.3V-1.4V=3.3V.

    This may can not turn on the upper bridge MOSFET, because UVLOGD Gate Drive UVLO maybe be triggered. (5% abnormal rate)

    Could you help to comment on this?

    Besides, whether there is any solutions for this if the 1.4V leakage voltage is always be there?

  • 0 in reply to Fabio Gou
    TI__Mastermind 48721 points

    Hello Fabio 

    I agree with you. You can confirm that the issue is caused by the BST_UVLO function or not, by connecting a battery (Vbat>4.4V) between BST and SW.  If the BST_UVLO function is the root-cause, you will be able to resolve the issue by using synchronous buck.

    Also, I think you can avoid the leak current (leaked by the communication port TX) flowing to the output of the buck converter by connecting a diode at the output of the buck converter.  

    -EL