L6258E View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6258E' PDF : 31 Pages View PDF
L6258E
Out_A and Out_B in case of low amplitude of the two triangular wave references.
The duty cycle has the max value of 100% when the input voltage is equal to the amplitude of the two triangular
references.
The transfer function of this block consist in the relation between the output duty cycle and the amplitude of the
triangular references.
Vout = 2 · VS · (0.5 - DutyCycle)
ACp wdB = 20 ⋅ log -∆-∆--V--V--o--i-nu---t = T----r--i-a----n---g---u---2-l-a---⋅r---V-A----Sm-----p----l-i-t--u---d---e--
ACp w dB = 10 ⋅ log -2---1-⋅--.-26----4- = 29.5dB
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.
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 :
Vsense
=
-----V-----o---u---t----
RL + RS
⋅
RS
so the gain of this block is:
ACload = V-----s---e---n---s---e- = -------R-----S--------
vout
RL + RS
ACloaddB
=
20
⋅
log
-------R-----S--------
RL + RS
AloaddB
=
20
⋅
log
-------0---.--3---3---------
12 + 0.33
=
– 31.4 d B
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 :
Fpole = ---------------1-----------------
2π
⋅
--------L----L--------
RL + RS
Fpole = -------------------1--------------------- = 163Hz
6.28
⋅
-1----2----⋅---1----0---–---3--
12 + 0.33
12/20
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