Oznog
Active Member
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.
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.