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DRV8870: Logic control

Part Number: DRV8870

Hi team,

Here's an issue from the customer may need your help:

As per the spec,  "When using PWM, it typically works best to switch between driving and braking."

You can actually drive the motor spinning with driving and coast switching as well.

The customer would like to know what is the difference between these two logical approaches and how to choose in a real application? Will the torque and output power be greater in driving& braking mode?

Could you help check this case? Thanks.

Best Regards,

Cherry

  • Cherry,

    For a DC motor, you want to use BRAKE to maintain the current in the motor when not in the drive state.  Current will decay quickly if you use coast and the system may not have the required torque needed for the application.

    Regards,

    Ryan

  • The customer would like to know what is the difference between these two logical approaches and how to choose in a real application? Will the torque and output power be greater in driving& braking mode?

    This driver has 4 integrated FETs for the H-bridge outputs, and the control input logic is a little unusual in a sense that for motor current control, the lower FETs are PWM and the higher FETs for direction control. The PWM logic is reverse, that 0% is max motor current and 100% give minimum current.

    I would use Brake instead of Coast, as the former uses the lower FET turned on for synchronous current instead of the body diodes to conduct the flywheel current as in Coast method, as the body diodes can be damaged. 

    To implement this Drive/Brake mode, it needs the controller with 2 pwm output pins connected to the chip inputs. IN1 set to 1 for Forward and IN2 is PWM (reverse logic) for speed control; IN2 set to 1 for Reverse and IN1 PWM to control speed. 

    I don't like this logic control table.

    Brian