Why is the L6470 getting hot?

[Nathan Coon]

Posted on July 21, 2017 at 18:13

I am using the X-NUCLEO-IHM20A1 board. The stepper motor that I am driving is a PK296A2A-SG36.

Resistance (Ω/phase) = .96 [Bipolar (Series)]

Inductance (mH/phase) = 6 [Bipolar (Series)]

Voltage (VDC) = 2 [Bipolar (Series)]

Current per Phase (A/Phase) = 2.1 per phase

I am using a 24V supply.

I used those values to get my Kval like this:

For full current:

Kval = (.96 * 2.1) / 24 = .084%

Kval is an 8 bit register so I found 20/255 = .08 so the register value should be 20 it I want to use the full 2.1 amps. When I use this value the L6470 gets really hot.

Currently I am only giving it the command run(1, 75) so it is quite low. It even gets hot when running at half kval = 10. I am not sure what is going on. Any help would be greatly appreciated.

[David Walker]

Posted on August 03, 2017 at 08:52

KVAL is not the only parameter for the L6470. It is a voltage mode controller and it computes the PWM duty cycle depending on the speed of the motor. For details, see the application note AN4144. To verify you aren't crazy, you could set the registers ST_SLP, FN_SLP_ACC and FN_SLP_DEC all to zero. Then, KVAL_RUN will specify the duty cycle for all speeds. Another factor that can scale the duty cycle is supply voltage compensation which is enabled in the option register. There are quite a few parameters that need to be specified to use this part, but if done correctly, I think it works well. 

David Walker

[Nathan Coon]

Posted on August 03, 2017 at 17:48

I will try setting those all to zero though I should have mentioned that I already used AN4144 to find all the parameters. I haven't done the fine tuning part but I think that the values should be close enough to not have this issue.