SI9961ACY_02 View Datasheet(PDF) - Vishay Semiconductors
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SI9961ACY_02 Datasheet PDF : 8 Pages
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Si9961
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. Si9961 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. Maximum retract
current may be calculated as:
0.66 V
IOUT + 175 x Iret + 175 x Rret
Head retract can be initiated automatically by an undervoltage
condition (either the 12-V or 5-V supplies on the Si9961) 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
Document Number: 70014
S-20883—Rev. G, 24-Jun-02
eliminate 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 signal since a power failure during this state may not
provide adequate spindle-motor back EMF to permit head
retraction.
Transconductance Amplifier Compensation
The Si9961CY features an integrated transconductance
amplifier to drive the voice coil motor (VCM). To ensure proper
operation, this amplifier must be compensated specifically 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.)
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