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LM5122: IC is heating up during standby and the standby current is abnormal.

Weiwei Su
Prodigy 230 points
Part Number: LM5122

Tool/software:

Hi Team,

I've built a 32V 8A boost circuit from this IC, so far the it works out very good, except the IC itself seems like drawing power (around 50mA) and heating up (probably up to 32C in 25C ambient) when no load is attached, while the temperature is ignorable but I don't think LM5122 have that much of quiescent current? 

I have read https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1041259/lm5122-high-quiscent-current-lm5122 this post states that Fet losses can induce current draw when no load is attached. But, shouldn't be the low side fet gets heat up instead of IC itself?

Also another question, during full load the SW voltage can shoot up to 38V (because of overshoot), and my mosfets are rated at 40V but due to this fet is used in other places in the board I don't really want to select a dedicated 60V mosfet only for the boost circuit. Should a RC snubber is recommended to suppress the overshoot to avoid protential issue of damaging the mosfet?

  • 0
    TI__Mastermind 29750 points

    Hello Weiwei,

    Thanks for using the e2e forum.
    Regarding the light load efficiency:
    - Are you running the device in FPWM? (MODE pin selection)? If yes, this could be the reason why you have higher losses in light load operation. Switching to DEM or SKIP mode will increase output voltage ripple in light load, but will greatly improve efficiency

    Regarding MOSFET selection:
    I agree that 2V is a rather low margin. An RC snubber can indeed reduce the voltage overshoot at the switch node. Another alternative is to add gate resistance, which has the same effect. I can recommend to place at least footprints for both.

    Best regards,
    Niklas