I am still on my struggle trying to design my own Brushed DC H-bridge with all N-MOS, still in the research stage and burning mosfets left and right.
I have come across this T.I design ,relatively recent. The full document about their design is here.
On page 12 and pictured below is the schematic of the H-bridge portion.
My question is as follows: I see no schottky diodes protecting it from the proverbial inductive spike. How come?
I do see the zener and resistor network but the paper says:
a Resistor-Zener network is provided on the switch nodes of the driver to protect it from overshoots and undershoots
I assume this "overshoot" refers to overshoot due to the bootstrap circuit and not inductive spiking?
Could it be that if you drive an H bridge in a complimentary manner, where the top and bottom mosfets are driven opposite of each other this gives the inductive spike a route to ground on off times.
For examplel: If you turn Q2 and Q3 ON the motor spins one way and when you turn them OFF there will be inductive spike so if you then turn Q1 and Q4 ON the spike has a route to ground and to Vbus.
that is the only explanation i can think of why they dont have protection diodes...
and yes I understand there has to be deadtime to protect from shoot through and all of that but my question is why there are no diodes?
One more question is what is the purpose of the resistor and capactors highlighted inside the bridge?? are these what they call snubber circuits?