SI9961A Datasheet, PDF (4/9 Pages) Vishay Siliconix – 12-V Voice Coil Motor Driver

Si9961A
Vishay Siliconix
PIN CONFIGURATION AND ORDERING INFORMATION
R_INH 1
R_INL 2
I_SENSE OUT ₃
FAULT 4
V_CC 5
I_{RET 6}
EXT V_REF 7
V+ 8
RETRACT ₉
GAIN SELECT ₁₀
ENABLE ₁₁
V_{REF− 12}
24-Pin SOIC
(Wide Body)
Top View
24 RFB
23 IA2−
22 ^OA2
21 ^ISENSE ^(IN)−
20 ^{SOURCE B}
19 ^{OUTPUT B}
18 ^VDD ^{(Spindle Supply)}
17 ^{OUTPUT A}
16 ^GND
15 ^{SOURCE A}
14 ^GND
13 ^ISENSE ^(IN)+
ORDERING INFORMATION
Lead (Pb)-Free Temperature
Part Number Part Number
Range
Package
Si9961ACY
Si9961ACY-T1
Si9961ACY-T1—E3
0 to 70_C
SOIC-24
(Wide Body)
APPLICATIONS
Introduction
The Si9961A Voice Coil Motor (VCM) driver integrates the
active feedback and drive components of a head-positioning
servo loop for high-performance hard-disk applications. The
Si9961A operates from a 12-V ("10%) power supply and
delivers 1 A of steady-state output current. This device is made
possible by a power IC process which combines bipolar,
CMOS and complimentary DMOS technologies. CMOS logic
and linear components minimize power consumption, bipolar
front-ends on critical amplifiers provide necessary accuracy,
and complimentary (p- and n-channel) DMOS devices allow
the transconductance output amplifier to operate from ground
to V_DD. Two user-programmable, current feedback/input
voltage ratios may be digitally selected to optimize gain for
both seek and track following modes, to maximize system
accuracy for a given DAC resolution. An undervoltage lockout
circuit monitors the V+ supply and generates a fault signal to
trigger an orderly head-retract sequence at a voltage level
sufficient to allow the spindle motor’s back EMF-generated
voltage to supply the necessary head parking energy. Head
retract can also be commanded via a separate RETRACT
input. VCM current during retract can be user programmed
with a single external resistor. External components are limited
to R/C filter components for loop compensation and the
resistors that are required to program gain, retract current, and
the load current sense.
www.vishay.com
4
User-Programmable Gains
During linear operation, the transconductance amplifiers’
gains (input voltage at V_IN vs. VCM current, in Figure 1) are set
by external resistors R₃ ! R₅, R_SA, and R_SB and selected by
gain input. After selecting a value for R_SA and R_SB that will yield
the desired VCM current level, the High and Low feedback
gain ratios may be determined by the following:
ǒ Ǔ^{R5 1}
High Gain + _{R3 4 RS}
ǒ Ǔ^{R5 1}
Low Gain + _{R4 4 RS}
(GAIN SELECT Input = High)
(GAIN SELECT Input = Low)
Where R_S = R_SA = R_SB
Input offset current may then be calculated as:
1
I_OS + _{4 RS}
ǒ Ǔ ^ǒ
ǒ_RS
) R_IN^Ǔ
R_IN ^VOSA2
)
5 V_IAS3^Ǔ
Where R_IN = R₃ or R₄
Document Number: 70014
S-40845—Rev. H, 03-May-04