AN1625 STMicroelectronics, AN1625 Datasheet - Page 28

• Manufacturer Part Number: AN1625
• Description: L6235 THREE PHASE BRUSHLESS DC MOTOR DRIVER
• Manufacturer: STMicroelectronics

AN1625 APPLICATION NOTE
Figure 30. G
The relation between the speed reference voltage (V
(
for a given speed, the speed reference voltage to apply is:
Designing the speed loop, care must be taken choosing the values of R
a good compromise between static performance, dynamic performance, stability and torque ripple:
2.15.1 Static performance - Speed Regulation vs. Resistant Torque:
The relation between V
speed. To minimize the resistant torque effect the term (D + G -v · G
possible.
Figure 31 shows how the speed changes with the load torque, and percentage regulation error.
Due to the op-amp output voltage saturation, beyond a certain load torque value the system cannot produce
further torque, then the motor speed drastically decreases.
28/39
M
) is given by the expression:
135
180
1 . 10
1 . 10
25
50
45
90
50
25
0
loop
0
module and phase.
3
3
speed
, T
b
V
and
0.01
0.01
speed
M
=
M
=
-----------------------------------------------------------------------------------------------------------
D
shows that for a fixed speed reference, the load torque (T
V
------------------------------------------------------------------------------------------------------------
+
spee d
M
1 s
D
+
M


0.1
0.1
1
1
G
+
+
+
speed
–
G
G
------------------------ -
G
v
1
op amp
op a mp
+
f [Hz]
f [Hz]
–
G
–
–
v
), the load resistant torque (T
s
1
G
I
k
1


T
k
G
G
G
T
1
1
op a mp
1
1
G
------------------------ -
k
k
–
1
T
op amp
pullup
T
1 ·
+
–
–
k
s
T
T
fc
fc
b
, R
+
I
· G
T
fb1
b
op-amp
, R
fb2
10
10
) must be kept as high as
, C
b
fb
) and the motor speed
, R
1
and R
b
) affects the
2
100
100
obtaining