AN1625 STMicroelectronics, AN1625 Datasheet - Page 30

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

AN1625 APPLICATION NOTE
Figure 32. Speed response to a 1mNm resistant torque step
Figure 33. Speed response to a 1V speed voltage step.
2.15.3 Loop Stability:
The phase margin is defined as 180° minus the phase of Gloop at the cut frequency (where Gloop=1). It should
be at least 45° to guarantee the stability. In the example it's about 65°.
2.15.4 Reference voltage ripple:
Due to the tacho waveform integration, the reference voltage provided to the L6235 V
wave (see Figure 27). The ripple can be calculated through the approximate relation:
30/39
where DC is the duty-cycle of the square wave at the tacho output:
Since this reference voltage is the torque control voltage, the ripple should be kept as low as possible,
accordingly to others main parameters. In the example the ripple is about 60 mV.
8000
6400
4800
3200
1600
100
20
40
60
80
0
0
0
0
0.1
0.1
V
re f
0.2
0.2
=
speedref
----------------------------------------------------- -
DC
R
fb1
0.3
=
0.3
n t
---------------------------------- -
f
tacho
pulse
1 DC
t [s]
t [s]
2
0.4
0.4
–
C
fb
m
0.5
0.5
--------------------
R
1
R
+
2
R
2
0.6
0.6
,
0.7
0.7
ref
input is a triangular