Hello
I have a problem with the current limit circuit of the DRV8830. In order to simplify the problem I have connected the output of the drive on a variable resistor Rload. The drive is powered with a votage of 4 V.
I want to limit the current to 0.5 A. To meet this condition, I choose a sense resistor = 0.4 Ohm between Isense and the ground. If the resistror of the load Rload is greater than 4/0.5 = 8 Ohms, the expected current is smaller than 0.5 A and the output of the drive is ok (programmed voltage). If Rload is smaller than 8 Ohms the output is only 0.4 V. In this case the current is only 0.4/Rload which is far below than the expected limit (0.5 A). For instance with Rload = 6 Ohms the output current is only 0.06 A.
The datasheet says : "When the voltage exceeds a reference voltage of 200 mV for more than approximately 3 μs, the PWM duty cycle is reduced to limit the current through the motor to this value."
In my application, the PWM duty cycle is not only reduced to obtain the limit current : it is reduced much more than expected.
Furthermore the current limit seems to be measured by taking into account the voltage that power the drive and not the voltage that is programmed
Thank you for your help
Sincerly yours
Etienne