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LM25019: Which is used, Vcc or External bias

Hirotsugu Kobayashi
Mastermind 9540 points
Part Number: LM25019

Hi, team.

When VCC and external bias voltage is the same, which is used?

Best Regards,

  • 0
    TI__Mastermind 40040 points

    Hello Hirotsugu san

    What ever voltage is higher will end up sourcing the current, either the internal VCC or external VCC. In a rare situation if the voltages are exactly the same presented at the VCC pin,  the currents could share, but this situation is unlikely occur.

    Hope this helps?


    David.

  • 0 in reply to David Baba
    Mastermind 9540 points

    Hi, David.

    When internal VCC and external VCC is close, does the intenal regulator repeat on-off by a fluctuation of external VCC?

    Is there a hysteresis?

    Best Regards,

  • 0 in reply to Hirotsugu Kobayashi
    TI__Mastermind 40040 points

    Hello Hirotsugu san,

    The only hysteresis on the VCC is its UVLO that occurs at ~4.5V, and it has ~300mV of hysteresis.  In short, no, hysteresis up at the ~7.6V.

    Regards,

    David.

  • 0 in reply to David Baba
    Mastermind 9540 points
    Hi, David.

    Please answer my another question.
    When internal VCC and external VCC is close, does the intenal regulator repeat on-off by a fluctuation of external VCC?

    Best Regards,
  • 0 in reply to Hirotsugu Kobayashi
    TI__Mastermind 40040 points

    Hello Hirotsugu san,

    As mentioned, there is no VCC UVLO function occurring at 7.7V, and as a result,  if the voltages are exactly the same, the currents will share.

    The likelihood of the voltages being exactly the same is very unlikely, either the internal VCC or the External VCC will likely source all the VCC currents.  If the customer needs assurances regarding the external VCC supply sourcing all the VCC currents, they will need to have an external bias voltage above the maximum regulation point of 8.55V as stated in the datasheet.  Recommend following the guidelines in the datasheet for using an external VCC supply.

    I hope this helps?

    David.