I'm currently using a pair of IPT015N10N5 FETs in half bridge configuration, to drive a motor. The FET gates are driven by a UCC27211A-Q1 High Side/Low Side driver. I'm thinking that this particular driver is inadequate to drive these FETs. For those who will ask, yes, I calculated out the bootstrap CAP value, and that is as follows:
The gate driver must switch the full VDS range in accordance with the MOSFET’s tR of 30ns. So the gate driver must achieve a dVDS/dt with a QGD of 211nC in 30ns requiring a peak current of 7.03A (Ipk = QGD/tR). On the nominal side, driving the nominal gate charge of 169nC in 30ns requires a peak current of 5.6A, which exceeds the driver’s max ability of driving the FET, which is 4Apk.
But if I roll with this just to see what comes out of it…
Q_CB= Q_G+(Dt_CYCI_B )=169nC+(0.95*31.25E^(-6)*0.0065A)=362nC
So the total charge is 362nC to be supplied by CB.
The max allowable ripple of ΔVCB is 5% of VDD so the bootstrap cap value should be:
C_B=Q_CB/〖∆V〗_CB = 0.000000362/(0.05*15)=603nF
The closest value for this cap is 600nF, or 680nF. The current value is 330nF, so doubling that cap gives 660nF. This value was chosen.
Solving for RB (bootstrap resistor):
R_B= ((1-D_MAX )* t_CYC)/(5*C_B )=((1-.95)*0.00003125)/(5*0.00000066)=473mΩ
RB Can be a shunt as this value is negligible.
This has bumped the high side gate voltage 10V higher than the bus voltage. HOWEVER - I occasionally see it dip lower, around the max bus voltage. It's spastic and unpredictable... My motor hiccups all the time because of it.
With that being said, I need suggestions for a gate driver that can handle this FET... Any suggestions?
Link to Datasheets:
DESIGN REFERENCE for anyone who would like it.
