IHM08M1 Over current Comparators strange behaviour

[Roberto Giovinetti]

Hello everyone

I'm playing with IHM08M1, and I'm trying to increase current up to 40/50 Ampere (peak). Changing parameters in Workbench I can do it, and motor spin well, even under heavy loads. There's only a problem: I've to remove one LMV331 in the circuit otherwise Overcurrent signal will trigger BKIN on the MCU.

Using an oscilloscope, I noticed that the output of the open collectors comparators is not truly "digital": it is expected that signal stay at 3V3 until current*Rshunt is less than Vref, but it happens that this signal start to decrease when current increase in one phase. If the current increase "too much" this decreasement causes the BKIN detection, while current*Rshunt is minor of Vref.

I've tried to change capacitor (10nF) on comparators outputs, but I've not obtained improvements.

I've noticed this behaviour on 3 different IHM08M1, and I changed LMV331, to be sure that they weren't defective.

Does anybody know why of this strange behaviour? Maybe BKIN of the MCU can affect the behaviour of the comparators output?

Thank you in advance

I hope someone can help me.

Roberto

[LXian.0]

Hi ST team,

I having the same problem with Roberto too. My work around is by reducing the Vin from 35V to 24V. The motor able to spin well but the IHM08M1 very hot(40-50C) near the phase OUT3 track. I also suspect the LMV331 too sensitive to the Vshunt detection but I didn't remove it as the protection is needed for prevent damaging the components.

My application need to run at 48V so I need help to solve issue too.

Regards,

XH Low

[Roberto Giovinetti]

Hi XH Low

I've tried a lot of tricks, and in the end I found the solution: you need to connect pin2 of LMV331 directly to Vshunt ground. If current increase a lot, in fact, there's a resistance path that degrade signal on the inverting input of the comparators. If you don't do this, BKIN signal will fall down every time currents increase over a certain value.

Using this trick (I soldered wires directly from shunt to LMV331 ground pin) I was able to handle about 30A RMS (42A peak) without false overcurrent faults.

Roberto

[LXian.0]

Hi Roberto,

Great!!!! It works.

I've checked the IHM08M1 PCB pin 2 trace routing. U25 and U26 pin 2 ground track routed with some distance. This might be the cause of the far return path for LMV331.

Thanks.

REgards,

XH Low

[Roberto Giovinetti]

Hi XH Low

Happy that it works!

I think that current path from shunts to input capacitors at high currents create a difference quite big respect signal ground of LMV331, so signal at inverting input is bigger than "reality".

Enjoy it!

Roberto

[ASHAI.1]

hello

@Roberto Giovinetti​ hope you are good

i am using X-NUCLEO-IHM08M1 with NUCLEOF302R8 trying to spin 1kw hall senored based bldc motor. i am facing the same problem(over current+speed feedback) but i am even unable to spin the motor

I configure the board like this

for FOC JP1&JP2 Closed, J9 Open

first thhe speed feedback fault was due to the hall sensor input in ihm08m1 board which was wrongly pullup after analysing i made my own circuit now the speed feedback fault has gone but over current fault still remain the same

The readdable current in sensing parameters is 30A and in over current protection it is 31A .

the BKIN pin never goes low while this fault occurs i check through multimeter

i think the drive parameters needs to be rectified correctly

can you please help me in doing this. i am literally trying as hard as i can but no results

kindly share your opinion and if possible your parameters too

It might help me to configure and spinn the motor

any type of help will be appreciated

[Roberto Giovinetti]

Hello

Sorry for answer after a lot of days, but you know, it's a difficult time.

I'm sorry, but I don't use Hall solution. I understand that you have over current fault, but I think that is not possibile to check BKIN using a multimeter. You need to check it via an oscilloscope. The only way you can have this fault is BKIN going low.

As mentioned in my previous posts, the problem is the ground reference of LMV331.

Did you try to connect pin2 to Vshunt?

Roberto

[Laurent Ca...]

"STM32 Motor Control" topic added.

Best regards