Strange problem with L6208-based driver

[dteney]

Hello all,

I built a 3-axis driver for my bipolar stepper motors, but it's not working perfectly. I implemented the "typical application" given in the datasheet of the L6208, and also mentionned in an app note from the manufacturer.

See p19 of the datasheet: http://www.st.com/stonline/products/...re/ds/7514.pdf

The problem
- If I power up the board, then I start "jogging" in Mach3, the motor vibrates or move randomly in no precise direction.
- If I start sending pulses with the power OFF, then I turn on the power of the board, then the motor rotates smoothly in the commanded direction. But if I stop and restart again, the motor again vibrates or rotates randomly.

I tried to add more capacitors to improve filtering of the power supply but it didn't help. I'm running in full-step mode, but I wonder if switching to half-step would change anything.

I really don't know how to could solve this problem, so I'd be really glad to get some help.

Thanks in advance.

[moonrock]

Originally Posted by dteney - If I power up the board, then I start "jogging" in Mach3, the motor vibrates or move randomly in no precise direction.

Much like to failure of one of phases(a or b) during power up. If current in one winding is present, but in another is absent - motor is start to twitch and then can run to random direction.

Can you show oscillograms from SENSEA and SENSEB pins?

[dteney]

I can't, I don't have an oscilloscope.

What could be the cause of that ? What is really intriguing is that it works every each time if the card already gets pulses when it is turned on.

[moonrock]

Bulding PWM based designs without osc is really hard

Mmm. May be check again circuits around RESET, EN, VREF pins?

Or replace IC at all?

[dteney]

I checked the circuit around those pins, and I already changed the circuit, it didn't help. I already tried another motor, too.

Right now I'm using a stabilized 12V power supply. I measured the voltage, which is normally almost 12V, but it increases to a bit more than 13V when I try to make the motor rotate. Is it normal ? Could it be the cause of my problem ? I measured the voltage on the logic inputs (reset, enable, etc.) it always is +5V or 0V.

Thanks again for your help.

[dteney]

It works. I switched to half-step mode. I don't have an explanation but it works now.