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Question about LP8861-Q re-start up

kura
Genius 4680 points
Other Parts Discussed in Thread: LP8861-Q1

I have  questions about LP8861-Q1.

We can't re-start up LP8861-Q1 in below condition.They are using internal LDO(CLDO = 1uF)

VIN off ---> Vin on ---->normaly start up ----->Vin off ------>input capacitor discharge -----> Vin reach around 0.85V----->Vin on again ----> this device can't startup.

Waveforms are attached .We could find LDO pin is stay 0.85V,so I think this device can't enter to STANDBY mode.

Question1.

Please tell me the reason why this device can't re-start up in this case.

Question2.

When LDO pin  applied 5V from extarnal source ,please let us know voltage sequence of VIN and LDO.

regards,waveform.xlsx

  • 0
    TI__Guru 60242 points
    Kura,

    This thread has been moved to the LED Driver forum for more appropriate support.

    Regards,
  • 0
    TI__Genius 11020 points

    Hello,

    Based on the oscilloscope plots the FAULT pin is pulled low and at the same time it pulls the EN/VDDIO low. So the device cannot startup when the EN/VDDIO signal is low. It appears that the EN/VDDIO signal is too weak to stay high in case the FAULT signal goes low.

    When LDO is applied from the external source the startup sequence should be: VIN --> VLDO --> EN/VDDIO.

    Thank you.

    Best Regards,

    Tomi Koskela