Non-bootstrap PMOS/NMOS half-bridge mosfet driver

[bobstay]

Hi all,

First-time poster here, please be gentle! I'm looking for a device which I suspect has gone out of fashion.

I want to build a synchronous-rectifier DC-DC switcher which can go to 100% duty cycle (DC). I will need a gate driver chip for the mosfets, as I want to use quite a high PWM frequency. I can find all sorts of bootstrap-style gate drivers designed for using two N-channel fets, which use a capacitor to boost the gate voltage for the high-side N-channel fet. They also have an integrated dead-time generator to prevent shoot-through currents. But, I understand these won't work for me as they can't go to 100% duty cycle because they require some switching to recharge their bootstrap capacitor.

I therefore intend to use a P-channel high-side fet and an N-channel low-side fet. So, I want to find a gate driver chip that has the following characteristics:

- Dual gate driver for PMOS high-side and NMOS low-side half-bridge
- (This means both outputs are in-phase, barring dead-time)
- Single TTL PWM input
- Automatic dead-time generation
- Will allow me to go to 100% duty cycle with the high-side fet permanently on and the low-side fet permanently off

I've searched high and low on my favourite component suppliers' sites and semiconductor manufacturers' sites, without success. They have dozens of varieties of bootstrap-style devices for driving dual NMOS half-bridges, but none for PMOS/NMOS. Does anyone know if such a beast exists?

 

[PaulHolland]

look at microchip gatedrivers

 

[mtwieg]

You could just replace the bootstrap capacitor with an isolated DC supply. The driver chip won't know the difference.

Do you really need 100% duty cycle. It's pretty much unnecessary in a properly designed converter.

 

[bobstay]

You could just replace the bootstrap capacitor with an isolated DC supply. The driver chip won't know the difference.

I'm kinda trying to keep the parts count down as space is limited, so adding an extra dc supply would be difficult. Do you have a recommendation for a small device that can do this?

Do you really need 100% duty cycle. It's pretty much unnecessary in a properly designed converter.

The reason for the 100% duty cycle requirement is that this is to be a buck/boost h-bridge. As such, there will be two sets of mosfets, and two driver chips. At the changeover point from buck to boost, neither set will be switching, and both will be in continuous conduction with the high-side fets on.