Other Parts Discussed in Thread: DRV8323
Hi,
I'm designing a BLDC controller with the DRV8323RS and encountering thermal issues at mosfet level.
System description
This is a 1-sense design.
The mosfets are AON7262E - 60V 34A 6.2mohm
I stalled the motor to monitor phases and switching current (3-PWM mode):
| State | |
| HS_U | PWM |
| LS_U | !PWM |
| HS_W | Low |
| LS_W | High |
| HS_U | Floating |
| LS_W | Floating |
Equivalent circuit would be:
The DRV8323 Idrive current is configured based on recommended calculation (120mA/240mA). Dead time = 100ns, Tdrive = 4000ns, no fault detection.
Problem:
The high-side mosfet is overheating A LOT under light load. I designed if for a 10A application, but I have thermal overrun (20°C/s) at as low as 2A mean current.
Measurements:
I made measurements at 8% duty cycle (0.6A mean current) and 20% duty cycle (2.1 mean current). Measurements are identical:
- W phase & input current (nothing to note except the low-side mosfet being always active)
- U phase measurements. This is the phase which is in PWM.
- High side rise/fall times:
Analysis
- Conduction losses: <100mW
- Switching losses: switching at 24kHz, 10% duty cycle with switching times below 100ns, shouldn't be much...
- Diode losses: should not have any
I know the PCB is a bit minimalist in term of power dissipation but losses do not call for more room; especially under such light load (2A)
Thanks for the help
