The schematic below appears typical stepper motor driver application with NJM3770A. As seen in the diagram, the single channel stepper motor drivers NJM3717 and NJM3770A are not synchronized.
such PWM switching of one channel is totally independent of the other
channel. Sometimes switching of the two channels may cause audible noise
and vibrations from the motor.
Read more complete here in pdf for synchronizing the NJM3770A Stepper Motor Driver switching in the two channels so that interference and noise will be canceled (source: njr.co.jp).