Use of powerSTEP01 in “voltage mode�?

[Central SUPPORT]

We are developing an OEM board which is capable of driving bipolar stepper motors from 15 to 80Vdc 10A max, in voltage mode and current control. Our customers should be able to change the supply voltage (Vbus), operating mode (voltage or current), without changing the assembly of the pcb.

We use powerSTEP01, and we studied AN4144 “Voltage mode control operation and parameter optimization�?, but still have a couple of questions:

1. How can we use voltage compensation (see AN4144, section 1.3) in our application without having to change the resistance values of the divider bridge? 
2. Does the current measurement resistors (Rsens) have an influence in voltage mode? Can we leave them for both operating mode?
3. Is there another way to define "Ke"? I use the method described in section 2.1 of AN4144, it works well but for OEM customers of our system it might be difficult to implement. Any suggestion?
4. Is it possible to preset a maximum speed according to VS, I, L, R or Ke? If so, by what formula?
5. Is there any documentation similar to AN4144 for current control?

NOTE: This question and answer originated from a customer support case which was handled by us. We regularly review support cases and add any helpful ones here for all to benefit from.

[Central SUPPORT]

Our answer to your questions:   

1.     When the motor supply voltage is different from its nominal value, the motor phases are driven with an incorrect voltage. For applications where you require smooth motion it is better to use this compensation. In case of wide supply range I recommend you to use comparators and switch lower parallel resistors in voltage divider.

2.     You can assemble Rsens also in Voltage mode.

3.     Ke should be defined in motor datasheet. If not, you have to measure it via oscilloscope and i.e. hand turning. Indeed, this procedure requires some effort not so hard to make, see attached 2 slides. In fact, if the motor manufacturer is unknown, there is no easy way to calculate Ke.

4.     For maximum speed which you can achieve by bipolar stepper motor is in voltage mode

5.     For current control mode please see AN4158 “Peak current control with automatic decay adjustment and predictive current control: basics and setup�?

[shilchenbach]

Hello,
I found this interesting formula above in this thread, but I can#t figure out, what is the unit of n_max. If I use this formula for a typical stepper motor, I get a result of 0,000005787. Udc=24V, Ke=0,15V/Hz, Kstep=200.

What is the unit of n_max?

Thanks in advance,

Stephan