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LP8725: BUCK1 unused - can we safely depopulate these components?

Gerry Hawkins
Prodigy 40 points
Part Number: LP8725

Hello,

We are not using BUCK1 in our application (i.e. FB1 (pin E4), SW1 (pin E5)). Nonetheless, we have an inductor and capacitor fitted to this output as it is initially enabled at start-up, and we were unsure of the ramifications of removing these output passives.

  • Can you please confirm if we are able to remove the BUCK1 output components without compromising the behaviour of the PMIC?
  • If so, please advise of the required termination of the FB1 and SW1 pins

Kind regards,

Gerry

  • 0
    TI__Genius 17380 points
    Hi Gerry,

    I would not recommend depopulating those components. The device was not designed for enabled bucks to be unpopulated so behavior could be unexpected.

    My first thought is if you are using the RESET_N pin, it will be asserted by a power fault detection on BUCK1 which may prevent processor from booting. If you can disable BUCK1 with I2C it may allow RESET_N to be released though - datasheet isn't clear on whether fault detection is masked for disabled BUCKs but it usually is.

    I don't see anything specific other than that so you could try it out and see if it works but I don't know whether PMIC will boot as expected and continue running. If you want to try it, typically VIN is left connected to the supply but input capacitor removed, SW is left floating, and FB is shorted to either GND or a supply higher than BUCK1 with the second being preferred as the first may cause the BUCK to switch until it detects a "short circuit" (voltage on FB stuck at 0 V). I don't see overvoltage detection so with FB1 tied to a higher voltage it may even register as power good and let RESET_N go.