AN1625 STMicroelectronics, AN1625 Datasheet - Page 29

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

Figure 31. Regulated speed variations versus mechanical load.
2.15.2 Dynamic performance:
The loop bandwidth is the frequency range in which the loop gain is greater than 1 (0 dB). In the example it's
about 2.5 Hz. It expresses how fast will the loop regulate the speed after load changes.
The transfer function between the resistant torque and the motor speed is
while between speed reference voltage and speed we have:
Figure 32 and Figure 33 show how the speed changes after applying a 1mN resistant torque step and a 1V
speed voltage step, respectively
2.5 . 10
1.5 . 10
3.5 . 10
3 . 10
2 . 10
4
4
4
4
4
0.005
Vref=3.67 V
Vref=4.67 V
Vref=4.17 V
0.01
Resistant Torque (Tb) [Nm]
--------------- -
T
0.015
M
b
--------------------------
V
s
s
spe ed
M
=
0.02
s
------------------------------------------------------------------------------------------------------------------------------- ------ -
1
s
+
s
=
0.025
M
-----------------------------------------------------------------------------------------------------------
D
1
1
0.03
+
+
s
s


1
M
I
+
+
–
------------------------- -
G
------------------------ -
+
--- - G
D
1
1
o p amp
1
G
+
+
D
–
s
–
s
v
I
1
–
10
G


v
2
4
6
8
0
1
0
G
G
k
op amp
1
T
–
k
0.005
G
------------------------ -
T
1
op amp
AN1625 APPLICATION NOTE
+
–
s
G
0.01
Resistant Torque (Tb) [Nm]
1
I
k
Vref=4.17 V
T
0.015
,
0.02
0.025
0.03
29/39