On 25/01/2023 10:33, Jan Panteltje wrote:>> The workings of the driver are opaque to me; I assume there is some >> cleverness to justify the their existence else we would just use a >> single transistor. > > No, you likely need a totempole:The functional diagrams of the drivers suggest they are totempoles. Which is why I am better using an existing part rather than having invent myself.>> Do I need a gate driver with enough "zap" to match the MOSFET gate >> charge? > > Yes > > >> [Does the cleverness mean at high frequency the charge coming >> out is stored and fed back in on the next cycle?] >> Will the driver fuse? > > Well even in a totempole its drive will limit current. > > >> Will it run out of power halfway though switch on? > > ?If it stores energy and dumps over a few nano seconds it has both a current limit and a total charge. Microchip talk about having a big enough capacitor on the supply so I guess (lots of guessing because the device is opaque to me) it just dumps the external supply capacitor's charge into the gate charge. "A value of 1.0uF is suggested" says for TC442[12] and TC442[678]. Should it be matched to the capacitance of the gate?>>> My idea, get some MOSFET and play with it,,,,, >> >> Buy 10 at a time. Prepare for whiffs of smoke... > > Na, just measure one on the bench, Vgs versus Id at some Vdd voltage... etcI'm not sure how I measure a 30ns current event. I have bought 10x TC4428 to play with.
P-channel MOSFET gate driver
Started by ●January 21, 2023
Reply by ●January 29, 20232023-01-29
Reply by ●January 29, 20232023-01-29
On a sunny day (Sun, 29 Jan 2023 10:45:46 +0000) it happened James <news@oxdrove.co.uk> wrote in <tr5ios$2np4n$1@dont-email.me>:>On 25/01/2023 10:33, Jan Panteltje wrote: > >>> The workings of the driver are opaque to me; I assume there is some >>> cleverness to justify the their existence else we would just use a >>> single transistor. >> >> No, you likely need a totempole: > >The functional diagrams of the drivers suggest they are totempoles. >Which is why I am better using an existing part rather than having >invent myself. > > >>> Do I need a gate driver with enough "zap" to match the MOSFET gate >>> charge? >> >> Yes >> >> >>> [Does the cleverness mean at high frequency the charge coming >>> out is stored and fed back in on the next cycle?] >>> Will the driver fuse? >> >> Well even in a totempole its drive will limit current. >> >> >>> Will it run out of power halfway though switch on? >> >> ? > >If it stores energy and dumps over a few nano seconds it has both a >current limit and a total charge. Microchip talk about having a big >enough capacitor on the supply so I guess (lots of guessing because the >device is opaque to me) it just dumps the external supply capacitor's >charge into the gate charge. "A value of 1.0uF is suggested" says for >TC442[12] and TC442[678]. Should it be matched to the capacitance of >the gate? > > >>>> My idea, get some MOSFET and play with it,,,,, >>> >>> Buy 10 at a time. Prepare for whiffs of smoke... >> >> Na, just measure one on the bench, Vgs versus Id at some Vdd voltage... etc > >I'm not sure how I measure a 30ns current event. > >I have bought 10x TC4428 to play with.As I understand you just want to switch supplies with it. In that case switch time, when an external capacitor is present, may not be so important, milli-seconds would even be OK. Could easily be done with discrete I am sure. http://panteltje.com/panteltje/cb/ scroll down to the circuit diagram that switches a high power radio transmiter using a MOSFET and optocoupler. even added extra capacitance on the gate :-) Often small caps are used on IC pins just to prevent the chip oscillating or in other ways malfunctioning, it is called RF decoupling. But you have that TC4428 chip now, so just following their application note should be OK.
