AN1139 STMicroelectronics, AN1139 Datasheet - Page 49

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

Figure 35a. Mathcad Analisys of the Spindle Current Control Loop
1ST STAGE (OTA) TRANSFER FUNCTION :
2ND STAGE TRANSFER FUNCTION :
H2( ) n
A1
wz
wp
G( ) s
(
(
Cgd S( ) n
Cgs S( ) n
i
f( ) n
S( ) n
n
ZL( ) n
H1( ) n
Ci
Co
Ra
1
Rc Cc
gm1 Ro1
.
Cc (
.
, 1 1.01 6
A1
Cgs
1
.
Ci S( ) n
.
Cgd
0
1
.
10
Rc
.
.
2 i
. .
Lm S( ) n
A1
n
1
1
1
..
gm2
gm2
Cgd
.
.
.
Cds
Ro1
10
wp
wz
(
(
1
1
s
s
Cgd S( ) n
Cgs S( ) n
n
)
)
Ra
)
1
S( ) n
S( ) n
(
wp
.
wz
.
Cml Co S( ) n
Rm
Ci S( ) n
0
.
gm2
gm2
Ro2
)
1
.
Cgd S( ) n
Cml S( ) n
)
)
( Transfer function of OTA after compensation)
Cds S( ) n
(
.
.
Cml Co S( ) n
Ro2
.
1
A1
Fz
Fp
Ro2
=
)
1
ZL( ) n
3.18 10
.
Cgd S( ) n
Cml S( ) n
. 2
wz
. 2
1
wp
Cds S( ) n
(motor)
.
.
(OTA)
3
(
Ro2
.
Cgs
1
gm2
Cds S( ) n
Fz 3.183 10
Fp
ZL( ) n
1
=
=
)
.
3
Cgs S( ) n
Ro2
1
Rota
AN1139 APPLICATION NOTE
0
0
0
1
0
.
gm2
3
Cds S( ) n
Rota
1
.
Cml S( ) n
Ro2
1
Ra
Cml S( ) n
0
.
1
.
Rs
1
Rota
1
Cml S( ) n
Ra
Cml S( ) n
0
.
1
.
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