DRV8305: problem with current loop control of BLDC motor with FOC method

Part Number:DRV8305

Hello,

I am using sensored FOC method for controlling BLDC motor. In current loop,when I set the d axis current to zero and q axis current to something below the rated value, the motor starts to rotate and after few second the speed of motor began to decrease and finally the motor stops. when I look at the current of motor, it is constant and suddenly began to increase. so I want to know why it is happening?

Regards,
Mohammad.