AN1139 STMicroelectronics, AN1139 Datasheet - Page 48

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

AN1139 APPLICATION NOTE
8.0 APPENDIX
8.1
Following are the models and Mathcad analisys for the Spindle Current control loop, Spindle Speed control loop
and Voice Coil Current control Loop. The external component used are referred to the typical application depict-
ed in Figure #22. The 5.0 release of Mathcad has been used and a floppy disk with the three analisys is available
through the STMicroelectronics representative.
8.1.1 Spindle Current Control Loop
Figure #34 shows the Spindle Current Control Loop model used for the analisys. Figures 35a, 35b, 35c show
the Mathcad analisys of the loop.
Figure 34. Spindle Current Control Loop Model
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MODELS & MATHCAD ANALISYS
gm1
(User specified parameters)
(Device parameters)
Ro1
Rc
Cc
Rm
Lm
Rs
gm1
Ro1
Rota
Cml
Ra
Id
gm2
Ro2
Cds
Cgd
Cgs
A
Rc
Cc
4
110 10
. 5 10
10 10
0.3
130
1.2 10
5.3
20 10
5.3 10
30 10
30 10
0.6 10
2.7 Id
5.2
12 10
Id
10 10
.
.
.
.
.
.
.
3
.
.
.
.
9
3
3
6
3
12
x1
12
12
12
3
Rota
(External compensation resistance)
(External compensation capacitance)
(Motor's winding resistance - Phase to Phase)
(Motor's winding inductance - Phase to Phase)
(External sense resistor)
(Transconductance of OTA)
(Output resistance of OTA)
(Output resistance of OTA buffer)
(Miller capacitor value)
(Output resistance of predriver)
(Coil current)
(Transconductance of DMOS)
(Output resistance of DMOS)
(Drain-source capacitance of DMOS)
(Gate-drain capacitance of DMOS )
(Gate-source capacitance of DMOS )
(Gain of sense amplifier)
Cm1
x1
x4
Ra
Cgs
Cgd
gm2
Ro2 47.273
=
=
Rs
g m 2
0.895
Ro2
Cds
Lm
Rm