I have a BLDC controller built around MP6538. The schematic is almost 1:1 with the devboard, I use IRFB3077 transistors. The motors I use are small, 5-6A@24V, all phasing/hall sequencing is correct and the controller spins them both ways successfully, but only at full speed. When I try to decrease the PWM duty cycle NOTHING happens and down to around 60% the motor keeps spinning at full speed, somewhere below 60% the motor speed drops significantly, and at 49% it stops. At 52% it makes a roaring noise and speed jumps up occasionally for a moment. It happens with 3 sizes of motors and 4 separate boards, all checked for wiring/electrical issues.
I tried disconnecting my CPU board and giving it PWM from a bench generator - same problem.
Can anyone please help me with this?