Datasheet A8932CLWA Datasheet (Allegro)

RET REF

V

V

BEMF

GROUND

UV

SET

R

OUT P

OUT

SWITCH

IN

OUT

RETRACT

FAULT

MP

RESET

SIGNAL

SUPPLY

1

2

FLT

PROTECT

CIRCUIT

3

4

5

6

7

8

– +

9

N

SW

V

PROTECT

CIRCUIT

V

CC

REF

10

11

12

13

14 15

–

+

– +

2 V

Data Sheet

26300.2A†

8932-A

VOICE-COIL MOTOR DRIVER

Providing control and drive of the voice-coil motor used for head

28

RET SET

V

27

SENS

26

V

LOAD

V

25

SENS FB

24

SGND

N

23

OUT

P

LOAD

22

V

DD

SUPPLY

21

OUT

N

SGND

20

19

18

17

16

+

–

P

ACT

FB

PWR OFF

H GAIN

REFERENCE

ACT

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.

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

Dwg. PP-042B

ABSOLUTE MAXIMUM RATINGS

Supply Voltages, VCC and VDD............ 6.0 V

Output Current, I

(continuous) ........................... ±500 mA

Analog Input Voltage Range,

V

.................................... -0.3 V to V

IN

Logic Input Voltage Range,

............................... -0.3 V to +6.0 V

V

IN

Package Power Dissipation,

......................................... See Graph

P

D

Operating Temperature Range,

..................................... 0°C to +70°C

T

A

Junction Temperature, TJ............... +150°C

Storage Temperature Range,

T

................................ -55°C to +150°C

S

† 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.

(peak) ........... ±600 mA

OUT

CC

■ Class-B, 2 Ω r

at 500 mA Output

DS(on)

■ 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

Always order by complete part number, e.g., A8932CLWA .

8932-A

VOICE-COIL MOTOR DRIVER

FUNCTIONAL BLOCK DIAGRAM

ACT

ACT

REFERENCE

H GAIN

PWR OFF

FAULT

MP

RESET

FB

19

15

16

17

18

12

13

ERROR

AMP

–

+

POWER

CONTROL

LOGIC

PROTECTION

CIRCUITRY

53 2

TSD

SIGNAL

SUPPLY

14

V

I

SENSE +

2 V

RETRACT

CONTROL

28

CC

+

–

1611

POWER

AMP

I

SENSE –

LOAD

SUPPLY

22

V

DD

CURRENT-SENSE
AMP

REF.

REF.

4

VOLTAGE-SENSE

AMP

–

+

REF.

–

+

–

+

26

V

LOAD

20

SGND

P

23

OUT

P

21

OUT

N

24

SGND

N

25

V

SENS FB

27

V

SENS

9

IN

N

7

OUT

10

OUT

SW

8

SET

BEMF

UV

V

2.0

1.5

FREE AIR,

R = 66

1.0

0.5

0

25

ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS

50 75 100 125 150

AMBIENT TEMPERATURE IN °C

θJA

°C/W

Dwg. GP-034

V

FLT

RET REF

RET SET

OUT P

R

RETRACT

GROUND

SWITCH

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
Copyright © 1992, 1995 Allegro MicroSystems, Inc.

Dwg. FP-024D

8932-A

VOICE-COIL MOTOR DRIVER

ELECTRICAL CHARACTERISTICS at T

= +25°C, VCC = VDD = 5.0 V, V

A

REF

= V

= 2.0 V,

IN

Load = 150 µH/3.5 Ω (unless otherwise noted).

Limits

Characteristic Symbol Test Conditions Min. Typ. Max. Units

Error Amplifier

Input Offset Voltage V

Current Gain A

Current Gain Linearity E

Reference Voltage Range V

Voltage-Sense Amplifier

Voltage Gain A

Output Offset Voltage V

Current-Sense Amplifier

Amplifier Error E

Input Offset Voltage V

Output Drivers

IO

iH

A

iL

L(adj)

REF

VD

OO

VD

iO

I

= 0 mA ——±50 mV

LOAD

H GAIN ≥ 3.5 V 7200 8000 8800 —

H GAIN ≤ 0.7 V 1800 2000 2200 —

I

= 5 mA to 500 mA, Ai = A

OUT

I

= 5 mA to 500 mA, Ai = A

OUT

iL

iH

——±10 %

——±10 %

1.5 — 2.5 V

0.36 0.40 0.44 —

I

= 0 mA ——±25 mV

LOAD

(Rs x I

I

LOAD

/ (Ai x V

LOAD

= 0 mA, Ai = A

)) - 1 — 1.0 ——

SENSE

iL

——±25 mV

Total On Resistance

(Source + Sink) I

Retract Output Voltage Error E

r

DS(on)

OUT(PN)

I

= 100 mA — 2.0 2.5 Ω

LOAD

= 500 mA — 2.0 2.5 Ω

LOAD

V

OUT(P)

- V

OUT(N)

- V

RETSET

——±100 mV

Full Power Bandwidth BW -3 dB 1.0 ——kHz

Uncommitted Op Amp

Voltage Gain A

VS

— 91 — dB

Unity Gain Bandwidth BW — 1.0 — MHz

Max. Load Capacitance C

LOAD

— 40 — pF

Slew Rate SR — 4.2 — V/µs

Output Voltage V

V

Max. Output Current I

Input Offset Voltage V

O

OSW

O

IO

V

SWITCH

V

SWITCH

≤ 0.7 V 2.5 — 3.5 V

≥ 3.5 V 2.5 — 3.5 V

— ±250 — µA

— <±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 T

= +25°C, VCC = VDD = 5.0 V, V

A

REF

= V

= 2.0 V,

IN

Load = 150 µH/3.5 Ω (unless otherwise noted).

Limits

Characteristic Symbol Test Conditions Min. Typ. Max. Units

Miscellaneous

Supply Voltage V

V

Under-Voltage Lockout Voltage V

Fault Logic Output V

Power-On Reset V

Total Supply Current I

FAULT

I

FAULT

MPRESET

CC

Logic Input Voltage V

V

Thermal Shutdown Temperature T

Thermal Shutdown Hysteresis ∆T

CC

DD

CC

+ I

IN(0)

IN(1)

J

DD

J

Operating 4.5 5.0 5.5 V

Operating 4.5 5.0 5.5 V

VCC = V

V

V

V

V

V

DD

≥ 3.5 V ——500 mV

RETRACT

≤ 0.7 V 4.5 —— V

RETRACT

= 2.25 V — >20 — µA

FLT

≥ 3.5 V 4.5 —— V

RETRACT

RETRACT

≤ 0.7 V, I

= 1.5 mA ——800 mV

MPREST

3.9 4.2 4.35 V

Outputs Balanced, No Load ——10 mA

Sleep Mode, PWR OFF = V

CC

——2.0 mA

——0.7 V

3.5 —— V

— 165 — °C

— 20 — °C

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 [phone]

VOICE-COIL MOTOR DRIVER

TERMINAL FUNCTIONS

Term. Terminal Name Function

1 RET REF The reference supply for setting the voltage across the load during retract.

8932-A

2V

3V

FLT

BEMF

Reservoir (energy storage) capacitor used to operate fault circuitry.

Back-EMF voltage from spindle motor used to retract heads during loss of power.

4 GROUND Circuit reference.

5UV

SET

Under-voltage trip point reference input. Set internally to 4.2 V but may be overridden by
external resistor divider. (Equation 4).

6R

OUT P

Source driver used for retract; externally connected to OUTP.

7 OUT Output of uncommitted operational amplifier.

8 SWITCH Logic input for transmission gate; a high level connects OUT to OUTSW.

9INNInverting input to uncommitted operational amplifier.

10 OUT

SW

Transmission-gated output of uncommitted operational amplifier.

11 RETRACT An active-low logic input that initiates the retract sequence.

12 FAULT A logic low at this MOS output indicates a thermal shutdown, under-voltage fault, or retract

command.

13 MP

RESET

(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.

14 SIGNAL SUPPLY VCC; low-current supply voltage in the range of 4.5 V to 5.5 V.

15 ACT Input which controls the current in the load. Transconductance gain is set with an external

resistor in series with this input (Equation 1).

16 REFERENCE V

; reference input for all amplifiers; ac ground.

REF

17 H GAIN Logic input to switch the error amplifier transconductance gain: LOW = 2000,

HIGH = 8000.

18 PWR OFF An active-high logic input that puts the device in a “sleep mode”.

All fault circuitry remains active.

19 ACT

20 SGND

21 OUT

FB

P

N

Input connection for feedback network which sets the error amplifier gain and bandwidth.

Power ground for the OUTP sink driver.

Power output. Sinks current when V

ACT

< V

REF

.

22 LOAD SUPPLY VDD; high-current supply voltage for the voice-coil motor.

23 OUT

24 SGND

25 V

SENS FB

P

N

Power output. Sinks current when V

ACT

> V

REF

.

Power ground for the OUTN sink driver.

Input connection for feedback network which sets the current-sense amplifier gain and
bandwidth. Also called gm SET.

26 V

LOAD

An output voltage proportional to the load voltage. Used in conjunction with closed-loop
velocity control.

27 V

SENS

Voltage output representing load current (Equation 2). Also called MONITOR.

28 RET SET An external resistor divider to set the retract voltage across the load. Used in conjunction

with V

RET-REF

(Equation 3).

www.allegromicro.com

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 =

i

R

gm

(Equation 1)

A

where Ai is either 2000 (H GAIN = Low) or 8000 (H GAIN =
High).

The error amplifier’s bandwidth and load compensa­tion zero are set utilizing external resistor and capacitor
feedback components around the amplifier.

The actuator main loop compensation can be set by
applying a square wave and adjusting RZ and CZ for
optimum response.

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:

V

SENSE

=

A

LOAD

i

(Equation 2)

RS I

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.

The back-EMF voltage represents the velocity of the

actuator. By subtracting the I

LOADRLOAD

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 V
voltage across the load (AVD[V
so that V
R

as shown in the following equations:

LOAD

represents I

SENSE

V

LOAD

= -AVD ([I

V

= RS I

SENSE

while R3 is dependent on

LOAD

LOAD RLOAD

LOAD/AiL

OUTN

is proportional to the

LOAD

- V

]). RS is selected

OUTP

] + V

BEMF

)

where Ai = 2000 (H GAIN = logic Low)

OUTSW = 0.4 (V

R3 =

V

BEMF

=

V

IN

BW = 0.4

BEMF R1/R2

R2 R

0.4 Ai R

R2 R

Vgm

0.4 Rgm R

R1 KB KT A

2π R

S

where J is the moment of inertia, K

)

LOAD

1

i

J

VGM R2

is the back-EMF

B

motor constant, and KT is the torque constant.

Velocity loop compensation =
L

LOAD/RLOAD

= R1 C1 = R3 C2.

A = 2000 or 8000

i

V

1/R

IN

gm

+

∑

–

1/R

Vgm

A

i

0.4 R /R
1 2

K1

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

K /J

T1/S

..

Ø

V

BEMF

.

Ø

K

B

Dwg. OP-003B

8932-A

F

VOICE-COIL MOTOR DRIVER

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:

V

RET-SET

=

1000 + R7 + R

8

8

(Equation 3)

2 R

where R7 + R8 >> 1000 Ω.

When the sequence is operated, the output voltage is
forced to approximately V
then a fault command (“brake”) is sent to the spindle

to retract the heads, and

RET-SET

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.

TEST CIRCUIT AND TYPICAL APPLICATION

R

IN

REF

R ≥ 200 kΩ

gm

FAULT

V

V = 2 V

C

H GAIN

PWR OF

R

Z

Z

ERROR

–

+

X

POWER

CONTROL

LOGIC

AMP

TSD

2 V

V

CC

I

SENSE +

+

–

Power for the retract function is provided by the
rectified back EMF of the spindle motor by way of the V
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 V

terminal.

FLT

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:

2 (R5 + R6)

UV

=

TRIP

R

6

where R5 + R6 << 200 kΩ.

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.

+5 V

VOLTAGE-SENSE

AMP

–

+

V

REF

–

+

VOICE COIL

R

S

R

3

MOTOR

R

2

C

2

POWER

AMP

I

SENSE –

V

DD

CURRENT-SENSE
AMP

V

REF

BEMF

(Equation 4)

www.allegromicro.com

V

CC

BACK EMF FROM
SPINDLE MOTOR

PROTECTION

CIRCUITRY

R

5

R

6

RETRACT

CONTROL

R

7

R

8

V

DD

–

V

REF

+

RETRACT

DIODE FOR RETRACT FUNCTION
OTHERWISE SHORT TO SUPPLY

SWITCH

C

1

R

1

R

Vgm

X

Dwg. EP-041D

8932-A

VOICE-COIL MOTOR DRIVER

28 15

Dimensions in Inches

(for reference only)

0.0125

0.0091

0.2992

0.2914

0.020

0.013

0.0926

0.1043

7.60

7.40

1

0.0040

28

0.419

0.394

0.050

0.016

2

3

0.7125

0.6969

MIN.

0.050

BSC

0° TO 8°

Dwg. MA-008-28A in

Dimensions in Millimeters

(controlling dimensions)

15

10.65

10.00

0.32

0.23

0.51

0.33

2.65

2.35

1

0.10

2

MIN.

3

18.10

17.70

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.

1.27

0.40

1.27

BSC

115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]

0° TO 8°

Dwg. MA-008-28A mm