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LP2951-N: Error detection during shutdown

Brian West46
Prodigy 230 points
Part Number: LP2951-N
Other Parts Discussed in Thread: LP2951

When pulling the LP2951 shutdown pin low to disable the regulator, we noticed that the error (open collector output) pin is being pulled low. Does the error detection comparator circuit stay powered and active when the shutdown pin is pulled low (regulator disabled)? This is not explicity described anywhere in the data sheet but is very important for low power applications since the active low output with a pullup to an external supply will cause some quiescent current draw.

  • 0
    TI__Mastermind 23361 points

    Hi Brian, 

    When the Shutdown pin is low, the main control loop is off, but the reference voltage and the error detection error amp are still up. If you worry about the quiescent current through the error pin, you may consider pulling the error pin to the output rail through a resistor. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 230 points

    Hi Jason. Thanks for the quick reply confirming that the error detection is still active even when the regulator is shutdown. I would highly recommend that this "feature" be made more explicit in the data sheet. If you look closely at the functional block diagram on page 16 you can see that the shutdown signal only goes to the error amplifier, so technically it is shown, but it is not mentioned anywhere else. Typically, you would expect the entire part to be shutdown, especially an error detection circuit since there is normally no need for error detection when the regulator is off!

  • 0 in reply to Brian West46
    TI__Mastermind 23361 points

    Hi Brian, 

    Thanks for your feedback. I was also using the circuit diagram to locate the answer. I totally agree that this information needs to be more explicitly mentioned in the datasheet. I will put this request in our datasheet revision list and hopefully, it will be addressed in our next datasheet refresh. 

    Regards, 
    Jason Song