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LM74930-Q1: How to properly use the SW pin?

Jacob Wyrick
Expert 8365 points
Part Number: LM74930-Q1
Other Parts Discussed in Thread: LM74900

Tool/software:

Hi team - I have been reviewing a LM74930-Q1 implementation and I believe we've found a chicken-and-egg scenario. We want to connect our OV/UV sensing via a resistor ladder from SW to GND to feed the OV/UV pins on the LM74930-Q1. The goal is to remove the resistor ladder from always being tapped off-battery and have it be disconnected via the SW pin. The SW pin is connected to pin "A" via an internal switch and, when the device is on, "A" should be roughly connected to battery.

However, we think we've identified an issue.

The conditions to enable HGATE driver state OV pin and UV pin must be below/above their respective thresholds. However, if we are using a resistor ladder off of SW pin, then this would never be true because SW would always be off and OV/UV would both be biased to GND.

Is that accurate?

Is there a way to use the SW to do the OV/UV function or would those pins always need to be biased via another method?

Thanks,

Jacob

  • 0
    TI__Mastermind 47795 points

    Hi Jacob,

    You have understood the operation correctly.

    SW was expected to monitor the common source voltage.

    We can't really tap OV and UV ladders from SW. This is because LM74930-q1 is expected to withstand high voltage rails like 200V transients. This is achieved by OV pin usage and hence has to be directly tapped from the VBUS. IF we tap after HGATE from SW, high voltage will be seen on SW and OV and damage the device.

    You can consider using LM74900 where SW can be used.

    Regards,

    Shiven Dhir