I'm trying to design a high-power Buck-Boost converter, which is meant to convert a 45-63V input voltage into a "constant" 48V. The application requires quite high currents (up to 20A continuous). The input voltage is variable, but without rapid changes (it's actually an output from a 15S Li-Ion battery).

I plan to run the switches from a dedicated microcontroller. While looking for components, the only major problem I have is to find a good enough high-side MOSFET driver, that can accept my uC logic and drive FETs that are those 60V above.

Then I found MIC4102 half-bridge MOSFET driver. At first, it looked very promising, with the 100V range and accepting PWM on input. The one problem I have is the following paragraph from the datasheet (p. 13):

A low on the PWM pin causes the HO pin to go low after a short delay (THOOFF). Before the LO pin can go high, the voltage on the switching node (HS pin) must have dropped to 2.5V below the Vdd voltage. Monitoring the switch voltage instead of the HO pin voltage eliminates timing variations and excessive delays due to the high side MOSFET turn-off.

My question is, with the Buck-Boost topology, on the Boost side, and actually in any Boost topology, is that not a problem with HS always staying quite high? I might be wrong here, but I don't see how HS can ever go below Vdd with it being fed from the inductor. For reference:

boost side of a buck-boost mic4102 buck application


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