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LM5109B: Possibility for a direct path mode instead of switching mode

Max Trybunksyi
Prodigy 70 points
Part Number: LM5109B
Other Parts Discussed in Thread: TIDA-010042, LM5109

Good day, 

We are using the LM5109 driver solution in interleaved buck converter design (see attached schematic). We used TIDA-010042 as a reference, just FYI. 

Apart from the buck operation we also need to provide a direct path between input and output without any switching, basically a straight conductor connection. I'd like to know if it's possible to set FETs in a constant open/close mode by setting LM5109 control pins to a HIGH/LOW state for a long time (like hours), not switching as PWM? Does it seem like bootstrapping is an issue in this case? If yes - what would be the solution for us in this case, maybe another drop replacement driver or circuit modification?

Thank you in advance. 

1447.Schematic.PDF



  • 0
    TI__Intellectual 2100 points

    Hi Max,

    Thank you for reaching out and sharing the image of the schematic! Once Vin has approached Vout, you will want to turn on both high-side switches. With both switches pulled high, you will have a constant output of Vin = Vout, and there should be no switching. This is because the output directly follows the input, so the output will be a constant high signal. To achieve this with 100% duty cycle, you will need an external charge pump (or some form of floating power supply) to help with charging the bootstrap occasionally.

    I hope this answers your question! Please let me know if you have any other questions or would like more clarification.

    Best,

    Alex Weaver