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LM5108: Can bootstrap-intended half-bridge drivers be used with an external power supply rather than bootstrap capacitor ?

Ben Gouhier
Prodigy 10 points
Part Number: LM5108
Other Parts Discussed in Thread: UCC27282, UCC21220, , UCC27288

I am looking for a half-bridge driver to control a pair of MOSFETs in a half-bridge arrangement. This is not a motor drive or a conventional use as the driving frequency of the bridge can go from DC to 20kHz. With such a frequency range, it is impossible to use a bootstrap capacitor as the high MOS can stay active virtually indefinitely.

I would like to know if drivers designed to rely on a bootstrap capacitor and either an external or internal bootstrap diode (such as the LM5108 or the UCC27282) can be used with an external power supply to allow DC operation, or if this is not compatible with the internal circuitry of the component ? I believe this should not be an issue as the bootstrap circuit is passive (diode + cap), but there may be some internal safeties or limits that prevent this ? I have used UCC21220 in the past, but I dont need the high voltage isolation nor the isolated low-side.

In general, if there are bootstrap chips able to handle this, how can I identify them ?

Thank you

  • 0
    TI__Intellectual 2100 points

    Hi Ben,

    Thank you for reaching out! It sounds like you will want to implement charge pump circuitry to help keep the boot cap charged. TI has a tech article available that helps explain the process for implementing a charge pump: Link. I am unaware of any internal mechanisms associated with using an internal bootstrap diode that would prevent using a charge pump. You will want to make sure the forward voltage rating and diode turnoff time are in-line with your system requirements.

    UCC27288 is a similarly rated half-bridge driver with no internal bootstrap diode. If you would like more flexibility choosing your boot diode, UCC27288 should help acheive this.

    Please let me know if you have any questions on implementing the charge pump, or any additional questions over either device.

    Best,

    Alex Weaver