TDA5345HT Datasheet, PDF (21/44 Pages) NXP Semiconductors – 5 V spindle & VCM driver combo

Philips Semiconductors
5 V spindle & VCM driver combo
Preliminary specification
TDA5345HT
Act+
I_{VCM VCM}
+ _<=>
I_VCM
V_VCM
Act+
R_VCM
L_VCM
Act-
Fig.13 VCM motor model
VCM
back-EMF
e
+
Act-
V_VCM=
(R_VCM
× I_VCM)
+


L_V
C
M
×
-d---I--d^V----^C_t---^M-- _
+
e
(8)
If the VCM current I_VCM can be considered as constant, the back-EMF becomes:
e= V_VCM – (R_VCM × I_VCM)
(9)
Figure 14 presents the VCM back-EMF amplifier as it is implemented in the TDA5345HT:
VcmMinus
(ext.)
Rsense
R2
(6)
(ext.) ⁽³⁰⁾
OpAmpInM
R1
(ext.)
I_VCM
(ext.)
(22)
VcmSenseInM
VCM
VcmPlus
(11)
Fig.14 VCM back-EMF amplifier
OpAmpOut
(31)
R
2R
R = 10 kΩ
VcmBemf
R
(29)
2R
(18) ^{VcmRef=1.482V}
The first operational amplifier output voltage (OpAmpOut) is:
OpAmpOut=
V
c
m
S
e
n
s
e
I
n
M
–_
RR-----12--
×
R_S
ens
e
×
I_VC

M
(10)
The VCM back-EMF amplifier output voltage (VcmBemf) is:
VcmBemf= 2 × (VcmPlus – OpAmpOut) + VcmRef
(11)
VcmBemf= 2 ×
V
c
m
P
l
u
s
–


V
c
m
S
e
n
s
e
I
n
M
–
〈
RR-----12--
×
R_S
en
s
e
×
I_V
C
M^〉


+ VcmRef
(12)
1999 June 10
21