Part Number: DRV8711
Dear Team,
we are using DRV8711 driver for brushed motor and i want to know the register configuration that suits to brushed motor. also please assist in velocity calculation for brushed motor. velocity calculation done in stepper motor as (microstepp*gear ratio)/step angle which is euql to 1 degree/sec so similary we need calcuation fro brushed motor also.
thank you for time.
Regards,
Padmaja
Hi Padmaja,
Thanks for your post in this forum.
we are using DRV8711 driver for brushed motor and i want to know the register configuration that suits to brushed motor.
For using the DRV8711 to drive a brushed DC BDC motor for each full-bridge A and B, you must set to Direct PWM Input Mode. PWMMODE bit in the OFF register must be set to 1b. See below information in the datasheet. The suggested control logic for BDC motor control in forward and reverse direction is indicated in the red rectangle box below. When the motor is not running both inputs AIN1, AIN2 and/or BIN1, BIN2 must be logic 1. This will also brake the motor by the low-side MOSFETs recirculation path also referred to as slow decay. For driving the BDC motor, one of the inputs must be logic 1 and the other must be PWM input. With this control setup motor output PWM is on when PWM input is 0 and motor output PWM is off when PWM input is 1. The PWM on/off ratio sets the duty cycle.
please assist in velocity calculation for brushed motor. velocity calculation done in stepper motor as (microstepp*gear ratio)/step angle which is euql to 1 degree/sec so similary we need calcuation fro brushed motor also.
Like you mentioned, velocity calculation for stepper motor requires gear ratio and step angle information from the stepper motor vendor. Likewise angular velocity of a BDC motor is directly proportional to the applied voltage and inversely proportional to the load torque. The vendor provides motor constant value Kv. Angular velocity ω = V x Kv. V is the voltage across the motor which would be supply voltage VM x PWM duty cycle. Some motor vendors provide BEMF constant Ke.
In this case Angular velocity ω = (V - (I x R)) / Ke. You can find a lot of academic information in the web regarding this BDC motor speed, torque etc. One example is this website.
With regards to the DRV8711, the motor velocity will depend on the PWM drive direction and its duty cycle and the coil current setting to limit startup inrush current will determine the acceleration time of the motor velocity based on the BDC motor formulae.
Regards, Murugavel
