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TPSM843A26: Issue output reduce and high ripple

Yuxi Liu(Tony)
Expert 3280 points
Part Number: TPSM843A26


Tool/software:

Hi TIer

My customer use tpsm843a26 in system.

Currently test we found a issue:

1. If output current large than 13A, the ripple voltage will be large suddenly. If I increase output current , the output voltage will reduce to 0.4V. If reduce the output current , the Vout will increase.

2. we try to change C889 to 3.9pF and the phenomenon is consistent. (not working)

Could you help check the sch and give some suggestion?

Thank you very much.

  • 0
    TI__Mastermind 24325 points

    The MSEL and FSEL pins should not have a capacitor to ground.   

    The capacitor can cause error in the pin strap reading at startup.

    Remove C889 and C608.   

    The MSEL resistor R699 is 22kOhm which sets the current limit to the lower setting, try using the higher current limit setting.

    Change R699. Use a 1.78kOhm or lower resistor.

    If problems persist, after these modifications, remove the ext sync resistor R696 and send waveform and board layout. 

    Capture plots:  Vout (dc coupled), SYNC,  Vout (ac coupled and trigger) to check switching frequency.  typically we used SW node but this is difficult on this device.