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LM27222: Problems driving a DAB

John Sullivan3
Prodigy 10 points
Part Number: LM27222

Hello,
I'm having some troubles with the LM27222 while driving a dual active bridge
Switching frequency: 250kHz
Input Voltage: 20V
Output Voltage: 20V
Output current: up to 5A

(There are actually 4 LM27222 for driving the 8 switches, I just draw 2 in this image)

The switches are sisa10dn

My circuit works, but 1 out of 3 times I burn a LM27222 at the output bridge during start-up.

It is always the same way that the LM27222 breaks: The pin 3 (CB) connects to the pin 8 (GND)

I tried putting a 6V zenner in the supply pin (6) to GND but it didn't work.
I'm attaching the (important part) of the schematics here, I can send some images of the layout if required.

Any ideas are welcome
Thank You

  • 0
    TI__Mastermind 20950 points

    Hello John,

    Thank you for the interest in the LM27222. From your description it sounds like you have some failures of CB to ground, only during startup conditions.

    Can you confirm if the same LM27222 device location fails, or do you have different IC locations? I ask that question since layout has a large impact on the possibility of voltage spikes and ringing.

    Since the failure happens on startup, and if it is a specific location, examine the voltage waveforms during startup, to confirm the device is within the datasheet ratings.

    Confirm that CB to ground is <33V, using a differential probe confirm that CB to SW is <7V, confirm that SW to ground is within the -2V to 36V voltage range. It sounds like you tried a Zener on VCC, but also confirm it is within the recommended 4V to 6.85V range.

    There is likely some voltage transient that only happens during startup, that may exceed the device ratings.

    Regards,