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LM5122: How to determine the operation mode

ACGUY
Guru 11170 points
Part Number: LM5122

Hello E2E,

I work in distributor at Japan. Our customer has issue for the boards they designed.
About LM5122-Q1, I have some questions.

 - Please let me know the how to check for internal operating mode.
 - Please let me know the how to restart up at pre bias.
 - In the datasheet, what is "VCC undervoltage threshold"? Is it the lower limit of the output of internal LDO?

Vin is fluctuate 30V -> 3V -> 32V in product spec when cold crank.
Currently, our customer designed circuit board can't operating normaly at restart Vin.
At then, Css voltage is less than 1.2V.
We guess that the cause of the restart failure is that the discharge of Css's charge is incomplete.

 - Does the circuit restart if discharging Css before restarting?

Regards,
ACGUY

  • 0
    TI__Guru* 78060 points
    Please show some key waveforms.
    -What do you mean by restart at prebias?
    -The VCC undervoltage threhold is a level when VCC is lower than that the IC will stop switching.
    -Once discharge of Css is triggered, it must complete before restart.