A8932: Voice-Coil Motor Driver

Data Sheet
26300.2A†
8932-A
VOICE-COIL MOTOR DRIVER
RET REF
1
V FLT
2
PROTECT
28
RET SET
27
V SENS
26
V LOAD
–
CIRCUIT
V BEMF
3
GROUND
4
25
V SENS FB
UV SET
5
24
SGND N
R OUT P
6
23
OUTP
OUT
7
VDD 22
SWITCH
8
E
L
B
A
E
L
L
I
A
A
V
S
A L
R
A
E
R
E
G
N
N
E
O
L G
R
O
N FO
+
–
IN N
Providing control and drive of the voice-coil motor used for head
positioning in 5 V disk drive applications, the second-generation
A8932CLWA is a full-bridge driver that can be configured so that its
output current is a direct function of an externally applied control
voltage or current. This linear current control function is supplemented
by additional circuitry to protect the heads and the data disk during
system failure or normal system shutdown.
9
OUT SW
10
RETRACT
11
FAULT
12
MP RESET
13
SIGNAL
SUPPLY
14
21
OUT N
20
SGND P
19
ACT FB
18
PWR OFF
17
H GAIN
+
16
REFERENCE
–
15
ACT
+
V REF
–
+
2V
PROTECT
CIRCUIT
V CC
LOAD
SUPPLY
Dwg. PP-042B
ABSOLUTE MAXIMUM RATINGS
Supply Voltages, VCC and VDD ............ 6.0 V
Output Current, IOUT (peak) ........... ±600 mA
(continuous) ........................... ±500 mA
Analog Input Voltage Range,
VIN .................................... -0.3 V to VCC
Logic Input Voltage Range,
VIN ............................... -0.3 V to +6.0 V
Package Power Dissipation,
PD ......................................... See Graph
Operating Temperature Range,
TA ..................................... 0°C to +70°C
Junction Temperature, TJ ............... +150°C†
Storage Temperature Range,
TS ................................ -55°C to +150°C
The two ±500 mA MOS driver outputs provide very low saturation
voltage and minimal power dissipation. Additional headroom is
achieved by the sense-FET structure eliminating the need for an external current-sense resistor. Internal circuitry can be configured to
provide closed-loop velocity control of the actuator by utilizing the
generated back-EMF of the voice-coil motor. Thermal protection and
under-voltage lockout disables the system in a controlled sequence if a
fault condition occurs.
FEATURES
■
■
■
■
■
■
■
■
■
■
■
Class-B, 2 Ω rDS(on) at 500 mA Output
Lossless Current Sensing
Zero Current-Loop Deadband
High Transconductance Bandwidth
User-Adjustable Transconductance Gain
Digital Transconductance Gain Switch (4:1 Ratio)
5 Volt Monitor with Selectable UV Trip Point
Retract Circuitry Functional to 0 Volts
Sleep Mode Function
Internal Back-EMF Velocity Loop Option
Internal Thermal Shutdown Circuitry
† Fault conditions that produce excessive junction
temperature will activate device thermal shutdown
circuitry. These conditions can be tolerated, but
should be avoided.
Output current rating may be restricted to a value
determined by system concerns and factors.
These include: system duty cycle and timing,
ambient temperature, and use of any heatsinking
and/or forced cooling. For reliable operation the
specified maximum junction temperature should
not be exceeded.
Always order by complete part number, e.g., A8932CLWA .
8932-A
VOICE-COIL MOTOR DRIVER
FUNCTIONAL BLOCK DIAGRAM
SIGNAL
SUPPLY
LOAD
SUPPLY
14
VDD
V CC
ACT FB
19
VOLTAGE-SENSE
AMP
22
–
I SENSE +
26
V LOAD
20
SGND P
+
23
OUT P
–
21
OUT N
24
SGND N
25
V SENS FB
27
V SENS
+
ERROR
– AMP
ACT 15
POWER
AMP
+
REFERENCE 16
2V
H GAIN 17
POWER
CONTROL
LOGIC
PWR OFF 18
REF.
CURRENT-SENSE
AMP
I SENSE –
–
+
REF.
TSD
FAULT 12
11
+
REF.
6
R OUT P
RET SET
1
RETRACT
28
RET REF
2
VFLT
3
–
RETRACT
CONTROL
4
8
GROUND
SWITCH
2.0
1.5
/W
R, C
AI 66°
EE =
FR JA
R θ
ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS
UVSET
5
VBEMF
MP RESET 13
PROTECTION
CIRCUITRY
1.0
0.5
0
25
50
75
100
125
AMBIENT TEMPERATURE IN °C
150
Dwg. GP-034
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 1992, 2001 Allegro MicroSystems, Inc.
9
IN N
7
OUT
10
OUT SW
Dwg. FP-024D
8932-A
VOICE-COIL MOTOR DRIVER
ELECTRICAL CHARACTERISTICS at TA = +25°C, VCC = VDD = 5.0 V, VREF = VIN = 2.0 V,
Load = 150 µH/3.5 Ω (unless otherwise noted).
Limits
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
—
—
±50
mV
Error Amplifier
Input Offset Voltage
VIO
ILOAD = 0 mA
Current Gain
AiH
H GAIN ≥ 3.5 V
7200
8000
8800
—
AiL
H GAIN ≤ 0.7 V
1800
2000
2200
—
IOUT = 5 mA to 500 mA, Ai = AiL
—
—
±10
%
IOUT = 5 mA to 500 mA, Ai = AiH
—
—
±10
%
VREF
1.5
—
2.5
V
Voltage Gain
AVD
0.36
0.40
0.44
—
Output Offset Voltage
VOO
ILOAD = 0 mA
—
—
±25
mV
Amplifier Error
EVD
(Rs x ILOAD / (Ai x VSENSE)) - 1
—
1.0
—
—
Input Offset Voltage
ViO
ILOAD = 0 mA, Ai = AiL
—
—
±25
mV
ILOAD = 100 mA
—
2.0
2.5
Ω
ILOAD = 500 mA
—
2.0
2.5
Ω
VOUT(P) - VOUT(N) - VRETSET
—
—
±100
mV
-3 dB
1.0
—
—
kHz
Current Gain Linearity
Reference Voltage Range
EL(adj)
Voltage-Sense Amplifier
Current-Sense Amplifier
Output Drivers
Total On Resistance
rDS(on)
(Source + Sink)
Retract Output Voltage Error
Full Power Bandwidth
EOUT(PN)
BW
Uncommitted Op Amp
Voltage Gain
AVS
—
91
—
dB
Unity Gain Bandwidth
BW
—
1.0
—
MHz
CLOAD
—
40
—
pF
Slew Rate
SR
—
4.2
—
V/µs
Output Voltage
VO
VSWITCH ≤ 0.7 V
2.5
—
3.5
V
VOSW
VSWITCH ≥ 3.5 V
2.5
—
3.5
V
Max. Load Capacitance
Max. Output Current
IO
—
±250
—
µA
Input Offset Voltage
VIO
—
<±10
—
mV
Continued next page…
Negative current is defined as coming out of (sourcing) the specified device terminal.
Typical Data is for design information only.
www.allegromicro.com
8932-A
VOICE-COIL MOTOR DRIVER
ELECTRICAL CHARACTERISTICS at TA = +25°C, VCC = VDD = 5.0 V, VREF = VIN = 2.0 V,
Load = 150 µH/3.5 Ω (unless otherwise noted).
Limits
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Miscellaneous
Supply Voltage
Under-Voltage Lockout Voltage
Fault Logic Output
VCC
Operating
4.5
5.0
5.5
V
VDD
Operating
4.5
5.0
5.5
V
VCC
VCC = VDD
3.9
4.2
4.35
V
VRETRACT ≥ 3.5 V
—
—
500
mV
VRETRACT ≤ 0.7 V
4.5
—
—
V
VFLT = 2.25 V
—
>20
—
µA
VRETRACT ≥ 3.5 V
4.5
—
—
V
VRETRACT ≤ 0.7 V, IMPREST = 1.5 mA
—
—
800
mV
Outputs Balanced, No Load
—
—
10
mA
Sleep Mode, PWR OFF = VCC
—
—
2.0
mA
VIN(0)
—
—
0.7
V
VIN(1)
3.5
—
—
V
TJ
—
165
—
°C
∆TJ
—
20
—
°C
VFAULT
IFAULT
Power-On Reset
VMPRESET
Total Supply Current
Logic Input Voltage
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
ICC + IDD
Negative current is defined as coming out of (sourcing) the specified device terminal.
Typical Data is for design information only.
The products described here are manufactured under one or more
U.S. patents or U.S. patents pending.
Allegro MicroSystems, Inc. reserves the right to make, from time to
time, such departures from the detail specifications as may be required
to permit improvements in the performance, reliability, or
manufacturability of its products. Before placing an order, the user is
cautioned to verify that the information being relied upon is current.
Allegro products are not authorized for use as critical components
in life-support devices or systems without express written approval.
The information included herein is believed to be accurate and
reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement of patents or other rights of
third parties which may result from its use.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
8932-A
VOICE-COIL MOTOR DRIVER
TERMINAL FUNCTIONS
Term.
Terminal Name
1
RET REF
2
VFLT
3
VBEMF
4
GROUND
5
UVSET
Under-voltage trip point reference input. Set internally to 4.2 V but may be overridden by
external resistor divider. (Equation 4).
6
ROUT P
Source driver used for retract; externally connected to OUTP.
7
OUT
8
SWITCH
9
INN
10
OUTSW
11
RETRACT
12
FAULT
13
MPRESET
14
SIGNAL SUPPLY
15
ACT
16
REFERENCE
17
H GAIN
18
PWR OFF
19
ACTFB
Input connection for feedback network which sets the error amplifier gain and bandwidth.
20
SGNDP
Power ground for the OUTP sink driver.
21
OUTN
22
LOAD SUPPLY
23
OUTP
24
SGNDN
Power ground for the OUTN sink driver.
25
VSENS FB
Input connection for feedback network which sets the current-sense amplifier gain and
bandwidth. Also called gm SET.
26
VLOAD
An output voltage proportional to the load voltage. Used in conjunction with closed-loop
velocity control.
27
VSENS
Voltage output representing load current (Equation 2). Also called MONITOR.
28
RET SET
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Function
The reference supply for setting the voltage across the load during retract.
Reservoir (energy storage) capacitor used to operate fault circuitry.
Back-EMF voltage from spindle motor used to retract heads during loss of power.
Circuit reference.
Output of uncommitted operational amplifier.
Logic input for transmission gate; a high level connects OUT to OUTSW.
Inverting input to uncommitted operational amplifier.
Transmission-gated output of uncommitted operational amplifier.
An active-low logic input that initiates the retract sequence.
A logic low at this MOS output indicates a thermal shutdown, under-voltage fault, or retract
command.
(Power-On Reset) A logic low at this open-collector output may be used to reset the
system on under-voltage fault or power on.
VCC; low-current supply voltage in the range of 4.5 V to 5.5 V.
Input which controls the current in the load. Transconductance gain is set with an external
resistor in series with this input (Equation 1).
VREF; reference input for all amplifiers; ac ground.
Logic input to switch the error amplifier transconductance gain: LOW = 2000,
HIGH = 8000.
An active-high logic input that puts the device in a “sleep mode”.
All fault circuitry remains active.
Power output. Sinks current when VACT < VREF.
VDD; high-current supply voltage for the voice-coil motor.
Power output. Sinks current when VACT > VREF.
An external resistor divider to set the retract voltage across the load. Used in conjunction
with VRET-REF (Equation 3).
8932-A
VOICE-COIL MOTOR DRIVER
DEVICE DESCRIPTION
Current Amplifier. The A8932CLWA voice-coil motor
driver features a wide transcon-ductance bandwidth and
minimal crossover distortion. The transconductance gain
is user selectable:
gm =
Ai
Rgm
(Equation 1)
where Ai is either 2000 (H GAIN = Low) or 8000 (H GAIN =
High).
The back-EMF voltage represents the velocity of the
actuator. By subtracting the ILOADRLOAD voltage component
from the voltage across the load, the back-EMF term can
be isolated and fed back to close a velocity control loop.
The amplifier output voltage VLOAD is proportional to the
voltage across the load (AVD[VOUTN - VOUTP]). RS is selected
so that VSENSE represents ILOAD while R3 is dependent on
RLOAD as shown in the following equations:
VLOAD = -AVD ([ILOAD RLOAD] + VBEMF)
The error amplifier’s bandwidth and load compensation zero are set utilizing external resistor and capacitor
feedback components around the amplifier.
VSENSE = RS ILOAD/AiL
The actuator main loop compensation can be set by
applying a square wave and adjusting RZ and CZ for
optimum response.
where Ai = 2000 (H GAIN = logic Low)
OUTSW = 0.4 (VBEMF R1/R2)
Current and Voltage Sensing. The load current is
sensed internally. Three auxiliary amplifiers are also
included to allow various control functions to be implemented. The first of these amplifiers provides a voltage
output that is proportional to the load current:
VSENSE
R I
= S LOAD
Ai
R3 =
R2 RVgm
VBEMF
=
0.4 Rgm R1
VIN
(Equation 2)
The second and third auxiliary amplifiers may be used
in conjunction with the first to provide a closed-loop
velocity control system for the actuator arm during a
controlled retract for head parking. This is achieved by
determining the back-EMF voltage generated by the voice
coil and feeding back this information to the main actuator
control input. The back-EMF feedback voltage can be
switched in as required by means of the SWITCH logic
input.
BW = 0.4
IN
1/Rgm
+
∑
Ai
R1 KB KT Ai
2π RVGM R2 J
where J is the moment of inertia, KB is the back-EMF
motor constant, and KT is the torque constant.
Velocity loop compensation =
LLOAD/RLOAD = R1 C1 = R3 C2.
A i = 2000 or 8000
V
R2 RS
0.4 Ai RLOAD
KT /J
..
Ø
.
Ø
KB
1/S
–
1/R Vgm
0.4 R1 /R2
K1
VBEMF
Dwg. OP-003B
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
8932-A
VOICE-COIL MOTOR DRIVER
Power for the retract function is provided by the
rectified back EMF of the spindle motor by way of the VBEMF
terminal. The A8932CLWA will perform the retract function under low supply conditions (nominally down to 2 V).
Operation down to almost 0 V requires an energy-storage
capacitor at the VFLT terminal.
Retract and Brake. A retract-brake sequence is initiated
on receiving a fault indication from the internal thermal
shutdown (TSD), or under-voltage lockout (UVLO), or an
externally applied logic High at the RETRACT input.
If the velocity control scheme is implemented, the
head can be retracted under the full control of VIN in
conjunction with OUTSW back-EMF voltage if no fault
condition exists. If a fault condition were to occur however, the retract velocity would be controlled by applying a
constant user-defined voltage across the load:
2 R8
1000 + R7 + R8
VRET-SET =
Protective Features. The A8932CLWA has a number of
protective features incorporated into the design. Undervoltage lockout provides system protection in the event of
reduced primary supply voltages. The under-voltage trip
point is internally set at approximately 4.2 V. It can be
user-defined with an external resistor voltage divider:
(Equation 3)
2 (R5 + R6)
R6
where R5 + R6 << 200 kΩ.
where R7 + R8 >> 1000 Ω.
UVTRIP =
When the sequence is operated, the output voltage is
forced to approximately VRET-SET to retract the heads, and
then a fault command (“brake”) is sent to the spindle
motor driver. The user determines the total time for the
retract sequence, before the spindle brake is enabled, by
the choice of an external resistor and capacitor at the
FAULT output.
Thermal shutdown circuitry is included to protect the
device from excessive junction temperature. It is only
intended to protect the chip from catastrophic failures due
to excessive junction temperature.
TEST CIRCUIT AND TYPICAL APPLICATION
+5 V
RZ
V CC
VOLTAGE-SENSE
AMP
VDD
–
I SENSE +
V
CZ
Rgm
ERROR
– AMP
IN
X
+
POWER
AMP
VOICE COIL
MOTOR
V REF
+
+
V REF = 2 V
–
2V
H GAIN
R FAULT
≥ 200 kΩ
I SENSE –
V REF
TSD
PROTECTION
CIRCUITRY
+
R
C2
3
R1
–
+
R Vgm
X
RETRACT
R5
R7
R6
BACK EMF FROM
SPINDLE MOTOR
RS
–
C1
RETRACT
CONTROL
VREF
V CC
R2
CURRENT-SENSE
AMP
POWER
CONTROL
LOGIC
PWR OFF
R8
VDD
SWITCH
DIODE FOR RETRACT FUNCTION
OTHERWISE SHORT TO SUPPLY
Dwg. EP-041D
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(Equation 4)
8932-A
VOICE-COIL MOTOR DRIVER
Dimensions in Inches
(for reference only)
28
15
0.0125
0.0091
0.419
0.394
0.2992
0.2914
0.050
0.016
0.020
0.013
1
2
0.050
3
0° TO 8°
BSC
0.7125
0.6969
0.0926
0.1043
0.0040 MIN.
Dwg. MA-008-28A in
Dimensions in Millimeters
(controlling dimensions)
28
15
0.32
0.23
10.65
10.00
7.60
7.40
1.27
0.40
0.51
0.33
1
2
1.27
3
18.10
17.70
BSC
0° TO 8°
2.65
2.35
0.10 MIN.
Dwg. MA-008-28A mm
NOTES: 1. Lead spacing tolerance is non-cumulative.
2. Exact body and lead configuration at vendor’s option within limits shown.
3. Supplied in standard sticks/tubes of 27 devices or add “TR” to part number for tape and reel.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
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