Overcurrent protection x-nucleo IHM08M3

[UVagl.1]

Is it possible to change the current protection threshold in motor control WB? if yes, how?

[Peter BENSCH]

The X-NUCLEO-IHM08M3 does not exist (typo?), so maybe you mean the X-NUCLEO-IHM08M1?

If that is true then the overcurrent protection is done using three comparators comparing the phase current voltages (Vshunt_x) with a reference voltage (Vref). Vref is derived using a voltage divider (R179/R180) from the 3.3V supply, as you can see in UM1996 (pg. 17) or in the schematics.

Does it answer your question?

/Peter

[UVagl.1]

yes, i mean X-NUCLEO-IHM08M1 with 3-shunt topology.

I read that document and looking at the schematic, Vref is 0.3V and Vshunt_x is a sine wave that oscillates between ± 300mV because Rshunt is 10mOhm. In these conditions Imax is 30Apk. So if I replace Rshunt with a smaller value (e.g. 5 mOhm) without changing Vref, I should have Imax = 60Apk right? or am I doing something wrong?

[Peter BENSCH]

Theoretically you could do it that way, but for that board it is not recommended to increase the peak current limit to those values. Please keep in mind this is just a board designed for evaluation and quick development and therefore tracks (width, thickness), connector etc are limiting factors.

A better idea is to design your own board if your need higher motor currents.

/Peter

[UVagl.1]

Of course this is an idea for my own board.

The problem is that I simulated the overcurrent circuit and the result is different from what I expected.

Motor control WB sets a default (max) PWM frequency of 30kHz, but in the V- input of comparator there is an RC filter with a cutoff frequency of about 2340 Hz. So the signal that actually enters in the comparator does not oscillate between ± 300mV, but between ± 30mV. If the comparator threshold is set it is set to 300mV, how can it work? Where am I doing wrong?

[Peter BENSCH · Accepted solution]

Maybe it's the 2.34kHz causing the mistake, where do you get it from?

The RC filter at comparators U24/25/26 is a simple low pass filter with a time constant of 68µs (680 ohms + 100nF), quite a good value for 30kHz PWM.

/Peter

[UVagl.1]

the input filter is fine, I got confused.

I tried to replace the shunt resistor with a 5mOhm one and I connected my motor to a variable load. checking the motor current and varying the load I tried to see if the overcurrent protection had changed but the current still cannot exceed 30Apk. how is it possible?

thanks

[Laurent Ca...]

Dear @UVagl.1​ 

Did @Peter BENSCH​ 's answers solve your problem?

If not, do you still have this problem to solve?

Best regards

Laurent Ca...

[Laurent Ca...]

Dear @UVagl.1​ 

As you do not answer, I guess you don't have to solve this problem anymore, therefore I consider this thread closed.

If not, feel free to reopen it by posting a new answer.

Best regards

Laurent Ca...