Dear,
I am currently busy with the design of an double motor controller that can handles two15amp brushed motors.
The power stage is designed around the DRV8702 gate driver, the schematic of the gate driver is shown below:
The software for the motorcontroller is finished and we are busy with doing a couple of tests to verify the firmware.
But when using an smaller DC motor there where some resonances visible
Blue trace is the switch node of one side of the half bridge, Yellow is the motorcurrent
At first it seems logical to have resonance by switching an inductive load as an motor but after looking more in detail to understand the resonances better it seems more strange.
The motor uses sign magnitude (or slow decay) so when the high side mosfet is switched on the motor current current can flow through the body diode untill the lowside mosfet switches on
So the current through the wires or motor is never interrupted of reversed so it's strange to see this large resonances.
The only parts i would expect to resonance is the switch node (the inductance of the connection/case with the mosfet drain) because there the current is suddenly switched between the two paths.
But this resonances should be much lower an high frequent then the resonances we see.
To test this theory we did some tests with another motor (24V 150W)
With this motor there is no resonance visible an there is only an small ripple current visible as expected.
Or are this resonances that we see internal generated motor resonances?
Already thanks in advance!
Kind Regards
Alexander
