I'm making a charge pump to provide a floating supply (to replenish the boostrap capacitor for the high drive MOSFET so it can maintain continuous gate drive).
I can use a 555 timer or some isolated charge pump circuit IC from ONSemi, but they all require a few too many components and I'm running out of room and need a few of these lying around the PCB. I was thinking I can cut out the timing capacitors and Vdd/Vss pins normally required on such ICs if I just use a CMOS pair and use a pin from the uC as the clock instead (please see diagram).
I only have one pin to implement this on (no software controlled dead-time), and it would somewhat defeat the purpose of minimizing components for this anyways if I used two pins. It would also very obviously defeat the purpose if I used gate driver ICs with dead time. So, I was thinking I could just place a resistor on the source of the PMOS to deal with shootthrough. I don't think any current realy flows through the PMOS- it's just used to float the capacitor to charge the floating cap.
Does anyone see a problem with this?
EDIT: Oh wait, the current that transfers charge between the caps passes through the resistor. Hmmm. ANd splitting the resistor between high and low side ends up speeding up the charge transfer a bit while slowing down the charging of the capacitor that gets boosted up. Does anyone know of a realy simple way to get around this? Maybe I should just size the resistor appropriately?
How do 555 timers deal with shoot through in their push-pull circuits? I'm pretty sure they don't have anything like that but I could be wrong.
I can use a 555 timer or some isolated charge pump circuit IC from ONSemi, but they all require a few too many components and I'm running out of room and need a few of these lying around the PCB. I was thinking I can cut out the timing capacitors and Vdd/Vss pins normally required on such ICs if I just use a CMOS pair and use a pin from the uC as the clock instead (please see diagram).
I only have one pin to implement this on (no software controlled dead-time), and it would somewhat defeat the purpose of minimizing components for this anyways if I used two pins. It would also very obviously defeat the purpose if I used gate driver ICs with dead time. So, I was thinking I could just place a resistor on the source of the PMOS to deal with shootthrough. I don't think any current realy flows through the PMOS- it's just used to float the capacitor to charge the floating cap.
Does anyone see a problem with this?
EDIT: Oh wait, the current that transfers charge between the caps passes through the resistor. Hmmm. ANd splitting the resistor between high and low side ends up speeding up the charge transfer a bit while slowing down the charging of the capacitor that gets boosted up. Does anyone know of a realy simple way to get around this? Maybe I should just size the resistor appropriately?
How do 555 timers deal with shoot through in their push-pull circuits? I'm pretty sure they don't have anything like that but I could be wrong.
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