E-L6258EA STMICROELECTRONICS [STMicroelectronics], E-L6258EA Datasheet - Page 16

• Manufacturer Part Number: E-L6258EA
• Description: PWM controlled high current DMOS universal motor driver
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

PWM current control loop
3
3.1
16/32
PWM current control loop
Open loop transfer function analysis
Block diagram: refer to
Input parameters:
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these data refer to a typical application, and will be used as an example during the analysis
of the stability of the current control loop.
The block diagram shows the schematics of the L6258 internal current control loop working
in PWM mode; the current into the load is a function of the input control voltage V
the relation between the two variables is given by the following formula:
where:
V
G
G
R
In this configuration the input voltage is compared with the feedback voltage coming from
the sense resistor, then the difference between this two signals is amplified by the error
amplifier in order to have an error signal controlling the duty cycle of the output stage
keeping the load current under control.
It is clear that to have a good performance of the current control loop, the error amplifier
must have an high DC gain and a large bandwidth.
DAC
s
in
s
V
L
R
R
R
C
Gs transconductance gain = 1/Rb
Gin transconductance gain = 1/Ra
Ampl. of the Tria_0_180 ref. = 1.6V (peak to peak)
R
R
V
L
S
r
L
S
C
C
a
b
= Internal reference equal to V
= 12mH
= 12Ω
= 40KΩ
= 20KΩ
= 24V
= 0.33Ω
= to be calculated
= to be calculated
is the resistor connected in series to the output to sense the load current
is the control voltage defining the load current value
is the gain of the input transconductance amplifier ( 1/Ra )
is the gain of the sense transconductance amplifier ( 1/Rb )
Figure 5.
I
LOAD
I
LOAD
I
=
LOAD
V
⋅
DAC
R S
· R
DD
/2 (Typ. 2.5V)
⋅
S
⋅
· G
-------
R b
--------------------- -
R a
1
S
R
⋅
=
= V
b
R s
V
DAC
DAC
=
· G
0,5
⋅
-------
R a
in
1
⋅
V
-------------- - A
R S
DAC
( )
DAC
L6258EA
, and