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LP2951: Input-output bypass

Mark Philip Felipe
Genius 11140 points
Part Number: LP2951
Other Parts Discussed in Thread: TPS746, TPS7A49,

Hi Team, seeking for some support.

Like to provide bypassing between the IN and OUT of LDOs. I am considering LP2951 LP38502 TPS746 TPS7A49 and/or TLV766, but I imagine the answer is applicable to any LDO.
Considering two typical LDO topologies with high-side BJT or FET.


1) With a FET switch, the input and output can be bypassed and can be any voltage within the recommended (output) operating conditions. If the LDO contains an active output discharge, the LDO must remain enabled to prevent the discharge circuitry from pulling a large current. If the LDO does not contain an active output discharge, the LDO may de enabled or disabled.


2) With a BJT, the input and output can be bypassed in two cases: In general, the output of the error amplifier must be high such that there is no current being sunk through the BJT base. The LDO must therefore be disabled and may not feature active discharge circuitry, or the LDO may be enabled if the bypassed output voltage remains higher than the feedback/configured output voltage.

Thank you.

-Mark

  • 0
    TI__Guru 50025 points

    Hi Mark,

    This concept could also be realized with an adjustable device. If you were to instead connect the FET (n-channel) drain to FB and source to GND, you can force the LDO into dropout when FB goes toward GND. Then you would get the bypassing without losing protection features like current limit and thermal shutdown. Would this be an attractive solution to you?

    Regards,

    Nick