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TPS22976: Problem with load switch for battery powered system

Julius Merz
Prodigy 10 points
Part Number: TPS22976

Hey TI,

we have a very small battery operated device, that will be powered by a small Li-Ion battery with a voltage from 3,3V up to 4,2V.

We want to use a button to turn the device on, than the device will be held on by a GPIO of a microcontroller for the duration the device is being used.

In the past we had an OR-Gate and a single channel load switch. In order so reduce the space needed on our PCB, we decided to go with the TPS22976N instead of the OR-Gate + Loadswitch.

SW1 will apply VBAT (3,3V up to 4,2V) to ON1. The load switch will turn on, VBAT_SWITCHED will feed to a LDO to turn the MCU on.

SYS_ON will be pulled HIGH up to 3,3V by the MCU. The button gets released and Channel 1 will turn off, while Channel 2 will carry the current.

I have chosen the Version of the TPS22976N that has NO output discharge, so it should be ok to tie channels together as back feeding is not possible VIN>=VOUT.

All capacitors are MLC and rated for at least 25V.

Can this be done?

  • 0
    TI__Mastermind 19340 points

    Hi Julius,

    Welcome to e2e!

    Nice use case. That should work fine, but one thing I would caution against is using the same CT capacitor for both channels - in general this is ok if both ON pins will be high at the same time, but the data sheet doesn't specify behavior when the CT pin is high voltage while the channel is disabled, so I can't guarantee it won't damage the CT driver. If you decide to continue with this device, I would recommend using separate CT capacitors for each channel.

    However, alternatively, you could use 2xTPS22992 - each package is 1.25mmx1.5mm compared to TPS22976's 3mmx2mm, and it has lower Iq, lower Rdson, and some extra features like PG should you need them.

    Please let me know if I can assist more with either solution.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 10 points

    Thank you very much Patrick, I have revised the schematic to use two capacitors as you suggested.

    Have a nice day!