About the zenner one, i think could use the circuit with supplies more than 15v, while keeping the gate at just 15v, as long as the current through the upper 30ohms resistor gives less power than rating of the zenner.
But, there should be no need to have the fall time with 2 paralel resistors, i dont see why. Normally the fall time is much shorter than rise time, but i guess somebody thought at something else. However different resistor rating means the lower transistor needs much bigger peak rating, which is probably not true - more likely it has same peak rating as the upper one.
The transistors peak rating gives the values of resistors, e.g. the resistors are there to limit the peak current to a value just under the transistor's peak rating.
The R57 i guess its there to take out the parasitic uC outputs like some pins read 1-2v even when they are off or not in use, and that could be enough to enable the transistors.
If it is ensured by design that the transistors cant be both on at same time, then it should be safe to merge the 2 resistors into just one. If mosfets are used instead of transistors, then could get rid of the R53.
There are some pnp and npn paired together in an 6pin-8pin packages, for both transistors and fets, dunno if there are any matches for this specific (?3.3v), but probably worth taking a look - besides pairing characteristics its also convenient packaging - as long as the board can use the layout as it is, without any vias.
But, there should be no need to have the fall time with 2 paralel resistors, i dont see why. Normally the fall time is much shorter than rise time, but i guess somebody thought at something else. However different resistor rating means the lower transistor needs much bigger peak rating, which is probably not true - more likely it has same peak rating as the upper one.
The transistors peak rating gives the values of resistors, e.g. the resistors are there to limit the peak current to a value just under the transistor's peak rating.
The R57 i guess its there to take out the parasitic uC outputs like some pins read 1-2v even when they are off or not in use, and that could be enough to enable the transistors.
If it is ensured by design that the transistors cant be both on at same time, then it should be safe to merge the 2 resistors into just one. If mosfets are used instead of transistors, then could get rid of the R53.
There are some pnp and npn paired together in an 6pin-8pin packages, for both transistors and fets, dunno if there are any matches for this specific (?3.3v), but probably worth taking a look - besides pairing characteristics its also convenient packaging - as long as the board can use the layout as it is, without any vias.