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LM5176: Lower VCC (Implemented)

James Dougall
Prodigy 30 points
Part Number: LM5176

Hi,

I've got an Application with Nominal Input voltage of 24V and Nominaly output of 35V. I'm ramping the Vout from 5V to 35V at startup with a PWM in the feedback.

I'm driving GaN FETS (GS61008T) and they have a Vgmax of 6V.

To enable 6V gate drive, I've got a 6V Zener regulator feeding Vin.

The regulator has been working reasonably well but I've damaged a few of the LM5176 during under voltage transients.

After damage, the device draws excess power from Vin, pulling the 6V zener reg down to ~1V or so. The device seems to 'retry' every ~1second or so. (much longer than the Tss/hiccup)

Has anyone attempted something like this?

Any thoughts on what's causing damage?

Cheers,

James

  • 0
    Prodigy 30 points

     

    Hey Stefan, Thanks for answering my last question about supplying the LM5176 with a lower voltage.
    I went ahead and implemented it. Any chance you have thoughts on what might be a problem?

    Also I saw your comment re. "LM5176: VCC Undervoltage Lockout"

    Unfortuntaely I didn't pop off the high side boost diodes to see if either of those drivers in the chip were loading down the 6V zener regulator.

    Thanks,

    James :)

  • 0 in reply to James Dougall
    TI__Mastermind 29710 points

    Hi James,

    Thanks for using the e2e forum and already getting in contact with Stefan.

    Regarding this circuit:
    The devices within our portfolio are not (yet) optimized for GaN drivers.
    I also do not have any reference design with this application from my side.

    If you say the damage happened during under voltage transients, it is indeed possible that the gate pins were overstressed below the abs min values and caused internal damage.

    To look further into this, it would be necessary to look at some waveforms to see have large and wide the peak actually are, to check if the device should be able to handle these peaks or if it is the root cause of the issue.

    Best regards,
    Niklas