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TPS62992-Q1: Large quiescent current increase in dropout kills my battery

Leonard Sherman
Prodigy 10 points

Part Number: TPS62992-Q1

Tool/software:

I was hoping to use the TPS62992-Q1 in alkaline cell powered device that needs to last a year or more between battery swaps. The device wakes up every hour for a minute of so but draws <1uA between wakes. The TPS device's 4uA quiescent operating current was the lowest I could find for a step-down that could handle the 4-cell max voltage of 6.6V. The problem I have discovered is that the TPS62992-Q1 quiescent current rises to over 1mA while in dropout! My circuit has no problem operating at lower voltages so I would like to run the batteries into the ground, but if the TPS62992-Q1 Iq rises to 1mA that will kill the cells in weeks or less when the pack voltage falls to 5V. I'd like to find a part with no Iq rise in dropout but this seems to be rarely (maybe never?) spec'd. I'm a bit surprised that dropout Iq rise is not mentioned more with so many battery powered devices being made.

  • 0
    TI__Intellectual 2230 points

    Hi Leonard,

    I will once check and get to you.

    Regards

    Rupayan

  • 0 in reply to Rupayan Saha
    TI__Intellectual 2230 points

    Hi Leonard,

    In dropout as the input voltage decreases to keep the output voltage of the buck regulated the duty cycle of the buck increases and as a result the on time of the high side fet will increase  to increase the duty cycle and it creates a low impendence path from input to output and as a result the dc inductor current/input current/Iq increases , so Iq rises . and also the gate driver has to be high most of the time to keep the high side fet on so also the iq rises.

    Regards

    Rupayan