Part Number:DRV8825
Hello, I'm having an issue with DRV8825 power dissipation and I would like to know if it is a normal operation or maybe we are doing something wrong.
VMA and VMB input voltage is 11.5V, and the value of sense resistors is 0.1ohms.
We are working in full step mode to move a nema 8 motor (winding resistor: 6.5ohms, current: 0.6A)
The VREF is set so the current per coil is 0.4A. The voltage and current measured per coil is (V = 2.94V and I = 0.4A) and the driver input current is 0.23A.
With these values the power delivered to the motor coils is 2*2.94*0.4 = 2.352W and the power at the input of the driver is 11.5V*0.23A = 2.654W
The power dissipated by the driver is 0.293W which differs a little from the thoretical value 4*0.3*0.4² = 0.192W calculated with the formula 4*RdsON*(Iout(RMS))²
If we change the VREF to get a current per coil of 0.05A the voltage and current measured per coil is (V = 0.375V and I = 0.047A) and the driver input current is 0.026A.
With these values the power delivered to the motor coils is 2*0.375*0.047 = 0.03525W and the power at the input of the driver is 11.5V*0.026A = 0.299W
The theoretical dissipation value by the driver in this case is 4*0.3*0.047² = 0.0026W and the measured dissipated power is 0.299W - 0.0325W = 0.264W.
Measurements of voltage and current are made using a multimeter. When the current to the motor is dissabled the current at the input of the driver is 4mA.
Is this a normal operation of the DRV8825? Does the efficiency decrease so much when the output current is reduced?
I'm almost sure that something is not correct in our calcs but I can`t figure out what.
Thanks