Running a BL-DC motor using DRV10963

I tried to run a BL-DC motor from MAXON P/N: 455020 using DRV10963, I applied a 4kHz PWM signal to the PWM input, I am using 3.3V as Vcc. When the power is applied the motor runs for about 1.5sec and stalls little more than 5 seconds and run again for same amount of time. Datasheet of the motor says no load current at 6V nominal voltage is 38.6mA, the current draw is about 260mA running from 3.3V supply when the motor runs which is lower than the current limit of the iC. I have captured the pulse output from FG pin when the motor runs there are exactly 59 for each run cycle separated by ~5.8sec ..see the two plots below. 

Any idea why it is doing like that.

Thanks,

Zahed Kabir