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rob23
rob23
Associate
February 11, 2014
Question

L6470 BEMF calculations

  • February 11, 2014
  • 2 replies
  • 835 views
Posted on February 12, 2014 at 00:59

Hi,

Is there an online version of the BEMF compensation tool?  I have a couple of boards from Sprakfun that are based on the L6470 but I'm having issues getting the performance out of the stepper motors that I thought I would be able to get.   Maybe I'm a bit dense but looking at the BEMF formulas I'm getting numbers that are ridiculously high so I must be messing something up somewhere. 

If there isn't an online version of the tool could someone possibly walk through an example of the calculations?  That way I could see where I'm going wrong and be able to apply the same calculations to other motors that I have as well.  

Thanks

#l6470
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2 replies

rob23
rob23Author
Associate
February 12, 2014
Posted on February 12, 2014 at 14:11

As an example this is what I am currently getting as a value based on the BEMF formula:

INT_SPEED = 4 *  Rm/2�?€Lm *  2^26 * ttick   where ttick == 250ns

Motor specs

Rm = 1.65

Lm = 2.8

Im = 1.68

INT_SPEED = (4*1.65/(2*pi*2.8))*(2^26)*250 = 

6293988307.48 

Does this seem correct?  Any of the other posts I've seen about INT_SPEED they seem to be using much lower numbers.

Thanks

Enrico Poli
Enrico Poli
ST Employee
February 17, 2014
Posted on February 17, 2014 at 16:34

Hi,

I think you forgot the order of magnitude of some of the parameters.

Inductance is expressed in mH and the tick time is in ns:

INT_SPEED = (4*1.65/(2*pi*2.8*10^-3))*(2^26)*250*10^-9 =

698830748

In any case you can use the attached document for the calculation of the parameters.

Best Regards

Enrico

________________

Attachments :

BEMF_compensation.xlsx : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HzI1&d=%2Fa%2F0X0000000bJM%2FXBYEO0lVfnTTdcR_klKHkTpFRhcgDFrEslLENaIewO4&asPdf=false
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