How to configure POWERSTEP01 ocd_th and stall_th?

[ARöss.1]

I've set up the POWERSTEP01 driver in voltage mode, which works nicely. Now I want to use the sensor less stall detection feature to implement sensor less homing. How must the stall_th and also the ocd_th values be dimensioned for this to work correctly.

Let's say for example I have a 1.68A stepper and my shunt resistor is 30mOhms. I've configured the hold current to be ~50% of the run current 1.68A using the formulas from application manual.

To calculate the voltages used in the register, I use U = R*I, v_stall = 30mOhm*1.8A = 0.054V, which results in stall_th register value of 1, meaning 31.25mV. Is this correct?

In general, how big shall the stall and overcurrent values approximately be for a stepper?

[dungeonlords789]

@Cristiana SCARAMEL​ 

[Cristiana SCARAMEL]

Hi @dungeonlords789​ ,

the powerSTEP01 SiP can manage 10 Arms and then higher peak current.

The overcurrent protection has been implemented to manage abnormal events (similar to current peaks).

The value of 38.46 A is an estimate given by the formula Ith = Vth / 2 x RdsON.

The real value is likely to be lower due to a higher value of RdsON that increases with the temperature.

If you need to set so high overcurrent threshold you still have to meet the limit of 10 Arms.

Let me know if I was able to clear your doubts.

Please, next time open a new topic to help the Community to address similar questions ;)

[dungeonlords789]

What is the point of such protection? Is it the protection of the driver when there is a short circuit in the motor? Or when the driver received more voltage than planned?

[Cristiana SCARAMEL]

As reported in the powerSTEP01 datasheet the overcurrent protection measures the load current of each half-bridge sensing the VDS voltage of the integrated MOSFET. You can find more details on the dedicated section 7.9 at page 29.

[dungeonlords789]

Datasheet says how to enable overcurrent protection. How does overcurrent may be in system? Is it the protection of the driver when there is a short circuit in the motor? Or when the driver received more voltage than planned? Or anything else?

[Cristiana SCARAMEL]

Hi @dungeonlords789​,

the protection in question concerns the power stage overcurrent.

Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of device (e.g. excessive load or failure in the shunt resistor).