SLG55021 no supply behavior

Hi Team,

I'm having a problem where a H bridge built using discrete parts is latching up while power is off on the control side.
Is it possible if 5V0 is not present on U26 below, Q12 gate is floating ( I have no units left, just trying to dig as deep as I can before I get some)?
This was a very rare event before and kept happening around 1 per 100 units, we kept adding protection everywhere, it did not make sense.
Today the customer changed their story and apparently this latchup happens even if the unit is not turned on or fw is not uploaded (5V0 rail is not powered).
VBAT is present even if the unit is powered off, it's a lead acid car battery.

Customer told me today, out of 9 units 3 failed after 2 minutes if they had them connected to the battery but the FW was not loaded.

thank you,
Kind regards,

  • Hi, 

    Can you share waveform for same? 



  • Hi,
    well apparently the gate of the Q12 floats if the SLG55021 has no supply.
    In my case sometimes it drifts into a territory, while the unit is switched off, where the whole bridge just latches up.
    A 3.0Meg resistor in between Q12 Gate and Source fixes the problem, we just have 600 all around the world waiting to fail. Even a x10 scope probe between gate and source the does the trick, though there's a 0.8V spike on the gate in that case.

    RED = Source. YELLOW = Gate
    We get around 6V of gate voltage with 3meg and 10meg in parallel loading it.

    kind regards,