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LP87524J-Q1: SW pin no switching soon after power on

PYTsai
Genius 11675 points
Part Number: LP87524J-Q1

Hi 

My customer had build 25 pcs of PCB and saw 10 pcs got issue that the output switch pin stop switching shortly (issue happen at SW_B0,B1,B2,B3 rendomly).

Below is the waveform we captured, any idea what might happen here ? 

Zoom In the above waveform as below

Finally the switching pin will settle at 0V as shown in below waveform

Below are customer's schematics, 

  • 0
    TI__Expert 8730 points

    Hi,

    Based on the scope plots provided, it is very difficult to provide any feedback on why regulators stopped switching.

    * Can you please ask them to probe, NRST and EN1 signal to make sure that these are not going down?

    * check the inductor current (or VIN current) to see whether it is hitting the current limit due to some short circuit on the board.

    * In this schematic, i dont see the input capacitors and have they placed those capacitors according to datasheet guidelines?

    Below are couple of points I noticed on the schematics, but in general, these should not cause the PMIC shutdown behavior

    * On the output side, we recommend atleast 2x22uF output capacitors on each regulator for improved stability.

    * For 5V input, we need snubbers on the switch pin.

    Regards,

    Murthy