L6258EX datasheet(18/32 Pages) STMICROELECTRONICS

18 / 32 page

PWM current control loop

L6258EX

18/32

Moreover, having the two references Tri_0 and Tri_180 a triangular shape it is clear that the

transfer function of this block is a linear constant gain without poles and zeros.

3.3

Load attenuation

The load block is composed by the equivalent circuit of the motor winding (resistance and

inductance) plus the sense resistor.

We will considered the effect of the Bemf voltage of the motor in the next chapter.

The input of this block is the PWM voltage of the power amplifier and as output we have the

voltage across the sense resistor produced by the current flowing into the motor winding.

The relation between the two variable is:

so the gain of this block is:

where:

RL = equivalent resistance of the motor winding

RS = sense resistor

Because of the inductance of the motor LL, the load has a pole at the frequency:

ACpw

224

⋅

1,6

-----------------

log

⋅

29,5dB

sense

out

----------------------

⋅

ACload

sense

out

---------------------

----------------------

ACload

----------------------

log

⋅

Aload

0,33

------------------------

log

⋅

31,4dB

–

Fpole

---------------------

⋅

-----------------------------------

Fpole

6,28

–

⋅

0,33

---------------------------

⋅

----------------------------------------------

163Hz

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