High side PMOS driver

[Oznog]

I have always done high side drivers for 12V, switched by 5V PWM, with a PMOS transistor controlled by an NMOS open drain inverted, pulled up with a resistor.

I have had cases where the switching time was too slow on the ON->OFF transition, where only the resistor pulls up against the gate capacitance. The PMOS gets quite hot with my high freq, high current buck converters. It's supposed to stay in saturation or cutoff and run fairly cool. I tried smaller pullup resistors, they did speed it up, but it's not a very efficient picture. It can take tens of mA to keep the PMOS on then. Now the resistors get hot.

Is there a better way to do this that I'm not aware of? I thought to use an inverter or buffer, there are some which work with 15V or more, but in that case the input has to be much more than 5V to constitute a logical "1". So I can't control it with 5V. Some have open drain outputs, which are of course no better than the NMOS open drain solution.

 

[Styx]

Why not use a dedicated MOSFET driver?

I use ICL7667 and they are very good (10ohm gate res to the MOSFET)

It takes in a logic signal and gives out whatever you have suppled to the output (usually 15V)


Also via ZENER re-referencing you can use it to drive a N-type held at -15V and turn-on with 0V

 

[Roff]

I have used the circuit below for driving capacitive loads. You might want to add a resistor from OUT to GND if you want a solid zero volts for the low state.

 

[Oznog]

Wouldn't touch a bipolar for power apps. Vcesat's like 0.3v, but using an NPN like that is far, far worse- over a volt. And it requires a lot of quiescent current either on or off... and it will reverse bias the base, which will kill it if it's enough voltage.

I'm looking more at those MOSFET drivers. A lot of them have really hefty quiescent current, something to watch if it's battery powered! They're also pretty pricey for a basic component. But I think there's some out there that can do the job.

What's this zener rereferencing?

 

[Styx]

Zener re-referencing (prolly not what it is really called but what we use at work)


For our specialist gate drives that need to switch IGBT of 500A + we use MOSFET drive output that we want switching v-fast. The ICL7667 is just a driver that we all use.

For teh P-type top drive one of these chips is supplied with GND and +15V.
So from a logic signal teh output switches between +15V and GND

for the N-tpye that is strapped to -15V and GND

we supply -15V (at teh GND input to re-ref its GND) and 0V to its high output rail.

It still takes a logic signal in but this logic signal w.r.t. GND which is now -15V.
So we put the 5V signal into the cathose of a 15V zener and the zerner anode to -15V its burn resistor (speedup cap across zener).

Now teh logic input of teh MOS drive sees -15V or -10V (or 0 and 5V w.r.t. its -15V GND) for a 0V and 5V (w.r.t. 0v GND) logic signal