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TPS782xx-3xx, TPS706 ground current in dropout

Phil Ekstrom
Intellectual 640 points

I plan to use a LDO regulator to protect my 3.6V (max) MSP430 from a 4.1V (max when charging) lithium ion rechargeable battery. It will be an always-on, mostly-sleeping,  solar-powered situation, so low parasitic drain is crucial. Good regulation is not important, but voltage limiting is. The TPS782xx and -3xx have suitably low ground pin current when regulating, and with a FET pass element they would not necessarily have the particular high parasitic (base current) drain that a PNP pass element has in dropout, but one never knows for sure that something similar does not occur unless the data sheet tells you. But these data sheets don't tell you. The plot of ground pin current vs. input voltage is admirably flat, but does not extend into dropout, where my regulators will be working when it is most important for them to have low drain.


Does the ground pin current stay low when the input voltage (2.7 - 4.1V) drops below the regulator set point of 3.0V? Is one of these regulators better than the others in this service? Is there an even better choice available?

Thanks, Phil

  • 0
    TI__Guru 55940 points

    Hi Phil,

    The increase in ground current in dropout is a side effect of certain LDOs caused when the LDO is attempting to regulate.  This point can vary depending on loading conditions (dropout is lower at lighter loads).  What are the loading requirements for your application?

    Very Respectfully,

    Ryan

  • 0 in reply to Ryan Eslinger
    Intellectual 640 points

    Ryan,

    What I care about here is the parasitic (ground pin) current drain when the MSP430 is in LPM3 and drawing about 2uA, and the battery source for the regulator is down below the regulator set-point of 3V, let us say the battery is at 2.8V, so the regulator is clearly in dropout and not successfully regulating. I'm not asking about the voltage loss in the regulator, just the ground-pin current.

    I'd like the regulator itself to also be drawing no more than a microampere or two of ground pin current when lightly loaded like that and in dropout. The data sheet does not tell me about the ground pin current under those conditions, so here I am asking.

    After taking a more careful look at the data sheets I see that I'll likely want to use the TPS78330 to avoid the output discharge load of the TPS78230.

    Phil