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TPS7A44: Bypass cuicuit on LDOs

Luke Sakamoto
Intellectual 2135 points
Part Number: TPS7A44
Other Parts Discussed in Thread: TPS7A43

Hi LDO team,

I would like to learn if below GPNs support bypass cuicuit.

-TPS7A44

-TPS7A43

Bypass means when Vin < set Vout, Vout will follow Vin as long as it is above the Vin recommended min value shown below?

i.e. When Vout is set at 6V but Vin becomes 5V, will is shut down? Or you will see the Vin (minus the internal FET RdsON Vdrops.)

Thanks,

Luke

  • 0
    TI__Genius 15125 points

    Hello Luke,

    Thank you for your question.

    Please allow me 2-3 business days to get an answer back to you.

    Best Regards,

    Hannah

  • 0
    TI__Genius 15125 points

    Hello Luke,

    I am seeing that the maximum dropout for the TPS7A44 is 800mV, so with headroom of 1V between Vin and Vout. Since Vin is dropping 1V below Vout, the LDO should not turn on when Vin drops that low. This seems to also be the case for the TPS7A43 part. Vin needs to be at least 1.5V higher than Vout for the part to align with datasheet specifications on features such as PSRR, noise reduction, etc... 

    Hope this helps!

    Best Regards,

    Hannah

  • 0 in reply to Hannah Grace
    TI__Intellectual 2135 points

    Hi Hannah,

    Hannah Grace said:
    Vin needs to be at least 1.5V higher than Vout for the part to align with datasheet specifications on features such as PSRR, noise reduction, etc... 

    Understood on having a headroom is required to be within the datasheet.

    My question was outside of datasheet, what happens when the Vin is below Vout? Will you see Vin - (internal FET Ron * Iout) = Vout for the output?

    I understand PSRR and other filtering are not guaranteed at all at this point.

    I am trying to understand the IC's output behavior in "Vout + headroom value"(specified in datasheet) > "below headroom" > Vin > "Vin UVLO".

    Thanks,

    Luke

  • 0 in reply to Luke Sakamoto
    TI__Genius 15125 points

    Hi Luke,

    Please see LDO Basics (Rev. A) (ti.com) for more information on dropout. 

    Best Regards,

    Hannah