SI9961A Просмотр технического описания (PDF) - Vishay Semiconductors
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SI9961A Datasheet PDF : 10 Pages
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Si9961A
Vishay Siliconix
12 V
System
Supply
V+ 8
5 V Ref
EXT
VREF 7 VREF_ 12
Back EMF Supply
VDD 18
mP
4 FAULT
5V 5
Voltage
Monitor
VR
Q1
VCC
8R
23 IA2- - A2
CL
+
R
+
A4
-
RL
VR
Q2
9 RETRACT
VR
6 IRET
Retract
Control
ENABLE
11 OA2
-
A5
22
Acceleration Error
RRET
R
VR
+
7R
GAIN 10
SELECT
mP
RINH RINL
12
RFB
24
A3 -
+
ISENSE ISENSE ISENSE
OUT IN+ IN-
GND
A
3
13 21 15 14
Q3
Q4
B
16 20
IOUT
VCM
17
OUTPUT
A
C2 R2
19
OUTPUT
B
R3 R4
R5
VIN
RSA
RSB
Figure 1. Si9961A Typical Application
Head Retract
A low on the RETRACT input pin turns output devices Q1
and Q4 on, and output devices Q2 and Q3 off. Maximum
VCM current can be set during head retract by adding an
external resistor between the IRET pin and ground. Maxi-
mum retract current may be calculated as:
0.66 V
IOUT = 175 × Iret = 175 × Rret
Head retract can be initiated automatically by an undervolt-
age condition (either the 12 V or 5 V supplies on the
Si9961A) by connecting the FAULT output to the RETRACT
input.
A high ENABLE input puts both driver outputs in a high-
impedance state. The ENABLE function can be used to elim-
inate quiescent output current when power is applied but the
head has been parked, such as a sleep mode. A sleep-mode
power down sequence should be preceded by a retract sig-
nal since a power failure during this state may not provide
adequate spindle-motor back EMF to permit head retraction.
Transconductance Amplifier Compensation
The Si9961A features an integrated transconductance
amplifier to drive the voice coil motor (VCM). To ensure
proper operation, this amplifier must be compensated specif-
ically for the VCM being driven. As a first approximation, the
torque constant and inertia of the VCM may be ignored,
although they will have some influence on the final results,
especially if large values are involved. (See Figure 1.)
Document Number: 70014
S-40845-Rev. H, 03-May-04
www.vishay.com
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