DRV8833C: DRV8833C

Hi Barry,

1. whats is I,FS(A) ?

I,FS(A) is the saturation current in the motor. This current is specified by the motor manufacturer.

2. what is the relationship between I,FS(A) and I,CHOP ?

I,CHOP is the maximum desired current driven through either winding. The maximum current in a brushed motor can be reduced to limit the current at startup and stall. Limiting the current during startup and stall can reduce the size of the bulk capacitor required.

When the motor is operated within the manufacturer specifications for voltage, the two terms have little meaning.

But if a motor rated for 5V is operated at 9V, the terms now have meaning. I,CHOP can prevent the motor current exceeding the manufacturer's specification. For example if the motor is rated at 5V and 40 Ohms, the current is 125mA. If VM is set to 9V, the current would be 225mA which could overheat the motor.

Using your example below, placing a 1.6 Ohm RxISEN resistor to GND limits the current to 125mA by comparing the voltage across the resistor to the internal 200mV reference. I,CHOP = 200mV/1.6Ohm = 125mA

3. The VM=5V , motor RL is 40 Ohm while the Motor has 2 phases (that can work in parallel) , current per phase is 0.15A .

meaning I,FS(A)< 124mA , while RXISEN=0.2V/(2*0.15A) = 0.2V/0.3A=0.666 Ohm

with the answer of #1,2 i would like to set the correct RXISEN value .

Using a 0.666 Ohm resistor with the motor described will probably have the same result as connecting the xISEN pins to GND. The reason is that you set the chopping current at 300mA (typical). If the VM is 5V in your system, the motor may never reach 300mA even when stalled.