DRV8718-Q1: Question about using independant half bridge

Hi Chase,

Thanks for your post.

Chase Jeong said:

• Is there any problem to control 1 DC motor for only one direction using only 1 half bridge of DRV8718-Q1? (In this case 1 half bridge remains as floating.)
• Or, Should I use remained 2 half bridges even I want to control DC motor for only one direction?

No issues to leave one of the half-bridges floating. The corresponding HBx must be set to HiZ to avoid a VGS, VDS fault report on that HBx because it may not have the FETs populated. 

Chase Jeong said:

And one more question. Is there any RPM limit if I control DRV8718-Q1 through SPI interface? (i.e. I use DC motor which maximum rpm is 1000, but DRV8718-Q1 can control only up to 800 rpm if I use SPI interface.)

For a BDC motor its RPM is determined by the PWM duty cycle if PWM speed control was used. Both pin control and SPI interface control support 100 % duty cycle which means the motor can run at full speed regardless of the interface. If PWM control is required pin control is recommended because to achieve a 20 kHz PWM the SPI must be written back to back pretty fast and may not be viable depending on the MCU resources. If only on/off 100 % duty cycle is required either pin control or SPI control can be used and achieve same results. Thank you.

Regards, Murugavel