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LM22672: LM22672 - Switch Node not getting to ground

Steven White
Prodigy 20 points
Part Number: LM22672


We are using LM22672 in a buck / inverter circuit stepping down from +24 V to ±16.8 V. We are seeing an issue on multiple boards where the switch node isn't going all the way to ground:

On a good board it does:

When this happens, the negative rail ends up shifted due to the DC offset on the switch node. What would cause this behavior?

  • 0
    TI__Mastermind 24195 points

    Hi Steven, 

    Thank you for sharing your scope shots and your schematic. Let me review this with the team and I will get back to you in a couple days. 

    In the meantime, can you send over a layout that might help us better diagnose your issue?

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    TI__Mastermind 24195 points

    Hi Steven,

    After conferring with the team the C834 capacitor may be interfering with the SW node waveform. Please test this design without the C834 and see what this does to the SW node waveform.

    If this does not work the problem may be that the device is asynchronous and you might need a synchronous device to make this topology work.

    Thank you,

    Joshua Austria