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LM5020: External VCC

Kuramochi Tadahiko
Guru 28715 points
Part Number: LM5020

Hi,

I heard that VCC must rise up after VIN rises up if VCC is supplied external rail.

Is it correct?

If yes, does this mean that VCC must rise up after UVLO of VIN is released?

Best Regards,

Kuramochi

  • 0
    TI__Guru* 78220 points
    Hi TQ,
    It is correct if your VIN pin does not have a block diode to stop the current back flow from VCC to VIN. There is a LDO producing VCC from VIN, and if VIN is not up but VCC is supplied, the body diode of the LDO will conduct.

    Hope this clarifies,

    Thanks,
    Youhao Xi, Applications Engineering
  • 0
    TI__Mastermind 21720 points
    Hi TQ,

    There shouldn't be a problem with supplying the VCC rail when VIN is low. If the VIN and VCC pins are not tied together there should be a blocking diode on the VIN pin to keep the VCC rail from backfeeding the VIN rail.

    If you are using an external rail to power the device it is suggested to tied the VIN and VCC rail together to minimize power dissipation. The UVLO can then be used to enable the controller when needed.

    Thanks,

    Garrett