my output DAC Voltage from LTC2644 varying continuously

i am using LTC2644 in motor control application. I am converting controlled PWM output to Analog Voltage by using LTC2644.But when feedback is connected to our system PWM Varies and Stabilize at one point,But my output DAC Voltage from LTC2644 varying continuously.

when feedback is not connected to our system generates 90% Duty Cycle constant.then LTC2644 giving stable output.

Is noise causing this problem?

what care should i take using LTC2644 in noise elimination?