I am designing a board to drive a DC micromotor which requires a 100kHz PWM signal. The board is mainly a digital design board, with very little analog signalling. I am planning on driving the motor with the STSPIN240 motor IC via an STM32 MCU. The supply voltage is 6V, I need a motor voltage of 4V98, i.e. drive the motor at 100kHz PWM at a duty cycle of 0.83 for the desired torque/speed characteristics at max load.
The signal tracking from the MCU to the motor IC will travel approximately 70mm. The motor IC PWM output goes to a daughter board via two male/female kk connectors + cable. It then goes from the bottom to the top of the board, ~30mm tracking, and comes off this daughter board via two male/female kk connectors + cable to the DC motor.
The board is a four-layer board. Signal, signal ground, power, signal. The steps I plan on taking for these signals:
- MCU PWM signals will be given dedicated tracks, will not use vias and will go as direct as possible.
- The ground plane in the PCB will provide the path for the the MCU PWM path.
- Any time a PWM signal crosses a signal it will cross it perpendicularly.
- The MCU output and input will be tracked directly to the connector (distance of <10mm)
- The MCU PWM output cables will be twisted, length of 30mm.
- The tracks on the daughter board will be tracked and via'd to the top layer for the second connector with <30mm of tracking.
- The cable to the motor IC is a ribbon cable, should this made into another twisted pair?
- When the signal goes to a connector the connector will be surrounded by via's to ground.
Do these layout considerations sound sufficient?