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LM5118 VCCX pin issue

Jacky Chen29
Genius 4735 points
Other Parts Discussed in Thread: LM5118

Hola,

Does VCCX pin of LM5118 will impact UVLO function if it without supply power source？

Below figures shows that our product UVLO is set to 3.9V, but the output voltage will not stable(around 9V～5V, 7V is normal) when input voltage drop down to 6V

even we floating the UVLO pin. If we re-connect VCCX pin to the output site and the UVLO function can works normally.

My question is the VCCX pin should be connected or left open, or it should be connected to the others power source？

                

Below figures are our schematic for your kind information and I think it should be no problem, does TI have any suggestion of it？

  • 0
    TI__Mastermind 21720 points
    Jacky,

    If I’m understanding correctly when the VCCX pin is not connected regulation is not achieved but when VCCX is connected to the output regulation is achieved with VBatt=6V.

    I would suggest connecting the VCCX pin to the 7V output when operating around VBatt=6V. It sounds like you may possibly be hitting the VCC under voltage threshold. By connecting the VCCX to the output voltage you are ensuring that this will not happen by locking VCC to 7V. By using VCCX you will also save power dissipation in the IC because the internal VCC regulator will not be used.

    Also as a side note I would suggest having a capacitor connected to VIN pin.

    Thanks,

    Garrett