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LMG5200: Operating the High-Side Gate with a PWM Duty Close to 100%

Duncan Stephenson
Prodigy 10 points
Part Number: LMG5200
Other Parts Discussed in Thread: SN6501-Q1

We want to drive the LMG5200's high-side gate with a PWM duty close to 100%. More specifically, every ten milliseconds, we wish to turn the high-side gate off for a microsecond or less.

After inspecting the datasheet, we understand that the device's bootstrap supply will not be able to support this operating mode. Because of this, we have considered connecting an isolated DC-DC converter to the device's HS and HB terminals. However, we are unsure how to do this in a way compatible with this device. 

In another LMG5200 discussion, it is stated that the device's bootstrap has an internal switch that only allows its internal capacitor to be charged to the required voltage. Therefore, could an isolated DC-DC converter with a 6V output be connected across the device's HS and HB pins, with a resistor used to limit current flow?

Is there any technical literature published by TI that describes the best way to achieve this?

  • 0
    TI__Expert 5635 points

    Hi Duncan,

    Yes, the LMG5200 can achieve 100% on time for the high side FET while using an isolated bias supply. We would suggest using an isolated bias supply output of 5V. 

    Best,

    Kyle

  • 0
    Prodigy 10 points

    Hi Kyle,

    Thank you for the reply and the suggestion to use a bias supply of 5V.

    Having looked through similar forum topics, I came across TI's SN6501-Q1, a transformer driver for isolated supplies. This appears to be a good fit for our application, which requires a low switching frequency of the half-bridge and, therefore, a low current requirement.

    Does this appear to be a sensible choice? We are considering the unregulated output design using one of the recommended transformers.

  • 0 in reply to Duncan Stephenson
    TI__Expert 5635 points

    Hi Duncan,

    Yes, this should be a good solution as long as the HB-HS voltage is between 4 to 5.25V as listed in the LMG5200 datasheet.

    Best,

    Kyle