DRV8701: heavy loaded Motor is stalling when the PWM is on low state

Part Number:DRV8701

I am using DRV8701E motor controller for my Controller circuit. also, I am using PIC18f87k22  microcontroller to a controller the commands and PWM (Oscillator: 64Mhz Internal , PWM frequency 30000 ). Everything is working fine but when the motor is driven with a heavy load, It is more likely to stall, specially when I set up Low PWM like 50 ( using Mikro C compiler ) the motor is stalling if it is heavily loaded but without a load, it's driven normally.  Is there anyway to fix this issue ? thanks