AN1139 STMicroelectronics, AN1139 Datasheet - Page 56

• Manufacturer Part Number: AN1139
• Description: L6254 - L6268 - L6269 12V DISK DRIVE POWER COMBO IC
• Manufacturer: STMicroelectronics

AN1139 APPLICATION NOTE
8.1.3 Voice Coil Current Control Loop
Figure #38 shows the Voice Control Loop model used for the analisys. Figures 39a, 39b, 39c show the Mathcad
analisys of the loop.
Figure 38. Voice Coil Current Control Loop Model
56/64
Device parameters
User specified value
DAC
Kamp
wamp
Ksen
wota
Lm
Rm
Rs
Ri
Kgm
Rf
BW
Cc1
Cc2
Rc
. 1 10
. 1 10
0.25
6.2 10
1.5 10
13.3
1.8 10
1.8 10
. 1 10
1
60 10
4
.
16
600 10
.
4
4
.
.
.
4
4
.
3
6
9
10
Ri
3
gain of power stage
pole of power stage
gain of sense amplifier
pole of OTA
coil inductance
coil resistance
sense resistance
input resistor
target DC loop transconductance(A/V)
feedback resistor suggested Rf value
target bandwidth(Hz)
compensation capacitance suggested Cc1 value
compensation capacitance suggested Cc2 value
compensation resistance suggested Rc value
Cc2
Rc
wota
Rf
Cc1
Ksen=4
wamp
Kamp=16
Rfs
Ksen Rs Ri Kgm
Rcs
.
Cc1s
Cc2s
Rs
.
Cc1 (
.
Rf (
.
Cc1
.
10
Rs
Lm
Ksen Rs Kamp
Rs
Rfs
Rm
.
Rm 2
=
Cc2s
1 10
)
.
)
. .
Rm
Rcs
=
4
1.8 10
.
BW
=
6.15 10
10
Cc1s
4
Lm
=
1.879 10
9