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LM5035C / external DC bias

K.Yaita
Guru 29720 points
Other Parts Discussed in Thread: LM5035C, LM5025A

Hi Team,

My customer considers applying external DC bias to both VCC and VIN for LM5035C.
In this case, Operating Ratings shows 8V(min) in page 5 of datasheet.


On the other hand, it is required more than 8.3V in page 11 of datasheet.



Which is the correct value?

Best Regards,
Yaita / Japan disty

  • 0
    TI__Mastermind 31580 points
    Hi Yaita-san,

    The 8V value is a recommended minimum value and does not represent the value of Vcc necessary to exceed the UVLO threhold. I would follow the figure in the text on page 11 or 8.3V.

    I would agree that the value is not very well explained in the datasheet.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    Guru 29720 points

    Hi Peter-san,

    I understood the external bias must be greater than 8.3V to exceed the VCC UVLO threshold for LM5035C.

    How about LM5025A and LM5027A?
    Should LM5025A and LM5027A also be applied more than 8.3V if applying external DC bias to both VCC and VIN?
    It seems these datasheet doesn't show the value of 8.3V.

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    Guru 29720 points

    May I have your comments about the following?
    --------------------------------------------------
    How about LM5025A and LM5027A?
    Should LM5025A and LM5027A also be applied more than 8.3V if applying external DC bias to both VCC and VIN?
    It seems these datasheet doesn't show the value of 8.3V.
    --------------------------------------------------

    It's my guess that LM5027A requires more than 9.5V (regulation point)...

    Your support would be appreciated.

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    Guru 29720 points

    Could you please support for this issue?

    Best regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Mastermind 31580 points

    Hi Yaita-san,

    The LM5025A datasheet states that the the internal regulator will be turned off when the voltage level on the Vcc pin is at 8V.

    This winding must raise the VCC voltage above 8V to shut off the internal start-up regulator.

    The LM5027A appears to have a different implementation. The outputs and reference are enabled when Vcc reaches 9.5V, the regulation value. To turn off the internal regulator the bias voltage from the auxiliary winding must be raise the pin voltage over the regulation voltage which drops from 9.5V to 7.5V after the first SR pulse is produced.

    Regards

    Peter