A8932CLWA-T - Allegro MicroSystems, Inc.

NO LONGER AVAILABLE

FOR GENERAL SALE

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.

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 exter-

nal 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.

VOICE-COIL MOTOR DRIVER

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

Data Sheet

26300.2A†

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

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

† 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.

14 15

28 RET SET

LOAD

SUPPLY

ACT

REFERENCE

H GAIN

PWR OFF

RET REF

GROUND

SWITCH

OUT

SIGNAL

SUPPLY

OUT

OUT P

SET

BEMF

FLT

SENS

LOAD

SENS FB

SGND

OUT

SGND

ACT

Dwg. PP-042B

RETRACT

FAULT

RESET

2 V

– +

–

– +

REF

PROTECT

CIRCUIT

PROTECT

CIRCUIT

8932-A

VOICE-COIL MOTOR DRIVER

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

50 75 100 125 150

0.5

ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS

AMBIENT TEMPERATURE IN °C

2.0

1.5

1.0

Dwg. GP-034

FREE AIR,

R = 66°C/W

θJA

FUNCTIONAL BLOCK DIAGRAM

–

–ERROR

AMP POWER

AMP

–

POWER

CONTROL

LOGIC

CURRENT-SENSE

AMP

Dwg. FP-024D

SENSE +

SENSE –

PROTECTION

CIRCUITRY RETRACT

CONTROL

TSD

SIGNAL

SUPPLY LOAD

SUPPLY

VDD

VCC

VOLTAGE-SENSE

AMP

2 V

14 22

REF.

ACT

REFERENCE

H GAIN

PWR OFF

FAULT

ACTFB

MPRESET 13

SWITCH

GROUND

VBEMF

UVSET

VFLT

RET SET

RET REF

ROUT P

532 281611

RETRACT

VLOAD

OUTSW

VSENS FB

OUTP

OUTN

VSENS

SGND P

SGNDN

INN

OUT

REF.

8932-A

VOICE-COIL MOTOR DRIVER

www.allegromicro.com

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

Error Amplifier

Input Offset Voltage VIO ILOAD = 0 mA ——±50 mV

Current Gain AiH H GAIN ≥ 3.5 V 7200 8000 8800 —

AiL H GAIN ≤ 0.7 V 1800 2000 2200 —

Current Gain Linearity EL(adj) IOUT = 5 mA to 500 mA, Ai = AiL ——±10 %

IOUT = 5 mA to 500 mA, Ai = AiH ——±10 %

Reference Voltage Range VREF 1.5 —2.5 V

Voltage-Sense Amplifier

Voltage Gain AVD 0.36 0.40 0.44 —

Output Offset Voltage VOO ILOAD = 0 mA ——±25 mV

Current-Sense Amplifier

Amplifier Error EVD (Rs x ILOAD / (Ai x VSENSE)) - 1 —1.0 ——

Input Offset Voltage ViO ILOAD = 0 mA, Ai = AiL ——±25 mV

Output Drivers

Total On Resistance rDS(on) ILOAD = 100 mA —2.0 2.5 Ω

(Source + Sink) ILOAD = 500 mA —2.0 2.5 Ω

Retract Output Voltage Error EOUT(PN) VOUT(P) - VOUT(N) - VRETSET ——±100 mV

Full Power Bandwidth BW -3 dB 1.0 ——kHz

Uncommitted Op Amp

Voltage Gain AVS —91 —dB

Unity Gain Bandwidth BW —1.0 —MHz

Max. Load Capacitance CLOAD —40 —pF

Slew Rate SR —4.2 —V/µs

Output Voltage VOVSWITCH ≤ 0.7 V 2.5 —3.5 V

VOSW VSWITCH ≥ 3.5 V 2.5 —3.5 V

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.

8932-A

VOICE-COIL MOTOR DRIVER

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

Miscellaneous

Supply Voltage VCC Operating 4.5 5.0 5.5 V

VDD Operating 4.5 5.0 5.5 V

Under-Voltage Lockout Voltage VCC VCC = VDD 3.9 4.2 4.35 V

Fault Logic Output VFAULT VRETRACT ≥ 3.5 V ——500 mV

VRETRACT ≤ 0.7 V 4.5 ——V

IFAULT VFLT = 2.25 V —>20 —µA

Power-On Reset VMPRESET VRETRACT ≥ 3.5 V 4.5 ——V

VRETRACT ≤ 0.7 V, IMPREST = 1.5 mA ——800 mV

Total Supply Current ICC + IDD Outputs Balanced, No Load ——10 mA

Sleep Mode, PWR OFF = VCC ——2.0 mA

Logic Input Voltage VIN(0) ——0.7 V

VIN(1) 3.5 ——V

Thermal Shutdown Temperature TJ—165 —°C

Thermal Shutdown Hysteresis ∆TJ—20 —°C

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

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 responsi-

bility for its use; nor for any infringement of patents or other rights of

third parties which may result from its use.

8932-A

VOICE-COIL MOTOR DRIVER

www.allegromicro.com

Term. Terminal Name Function

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

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

BEMF 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).

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.

9IN

NInverting input to uncommitted operational amplifier.

10 OUTSW 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 MPRESET (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 VREF; reference input for all amplifiers; ac ground.

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

20 SGNDPPower ground for the OUTP sink driver.

21 OUTNPower output. Sinks current when VACT < VREF.

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

23 OUTPPower output. Sinks current when VACT > VREF.

24 SGNDNPower 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 An external resistor divider to set the retract voltage across the load. Used in conjunction

with VRET-REF (Equation 3).

TERMINAL FUNCTIONS

8932-A

VOICE-COIL MOTOR DRIVER

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

0.4 R /R

1 2

A = 2000 or 8000

VBEMF

AiK /J

T 1/S KB

1/RVgm

–

1/Rgm

VIN

Dwg. OP-003B

∑

Current Amplifier. The A8932CLWA voice-coil motor

driver features a wide transcon-ductance bandwidth and

minimal crossover distortion. The transconductance gain

is user selectable:

(Equation 1)

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

High).

The error amplifier’s bandwidth and load compensa-

tion 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 imple-

mented. The first of these amplifiers provides a voltage

output that is proportional to the load current:

(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.

DEVICE DESCRIPTION

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:

where Ai = 2000 (H GAIN = logic Low)

VSENSE = RS ILOAD

VLOAD = -AVD ([ILOAD RLOAD] + VBEMF)

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.

VSENSE = RS ILOAD/AiL

gm = Ai

Rgm

OUTSW = 0.4 (VBEMF R1/R2)

R2 RS

0.4 Ai RLOAD

R3 =

VBEMF

VIN

R1 KB KT Ai

2π RVGM R2 J

BW = 0.4

R2 RVgm

0.4 Rgm R1

8932-A

VOICE-COIL MOTOR DRIVER

www.allegromicro.com

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 how-

ever, the retract velocity would be controlled by applying a

constant user-defined voltage across the load:

(Equation 3)

where R7 + R8 >> 1000 Ω.

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.

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 func-

tion under low supply conditions (nominally down to 2 V).

Operation down to almost 0 V requires an energy-storage

capacitor at the VFLT terminal.

Protective Features. The A8932CLWA has a number of

protective features incorporated into the design. Under-

voltage 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 4)

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.

2 (R5 + R6)

UVTRIP =

TEST CIRCUIT AND TYPICAL APPLICATION

2 R8

1000 + R7 + R8

VRET-SET =

–

VOLTAGE-SENSE

AMP

VOICE COIL

MOTOR

–

H GAIN

PWR OFF

SWITCH

ERROR

AMP POWER

AMP

–

POWER

CONTROL

LOGIC

PROTECTION

CIRCUITRY

CURRENT-SENSE

AMP

REF

Dwg. EP-041D

Rgm CZ

+5 V

RC2

RVgm

VIN

2 V

SENSE +

SENSE –

TSD

RETRACT

CONTROL

DIODE FOR RETRACT FUNCTION

OTHERWISE SHORT TO SUPPLY

BACK EMF FROM

SPINDLE MOTOR

R ≥ 200 kΩ

FAULT

RETRACT

V = 2 V

REF

8932-A

VOICE-COIL MOTOR DRIVER

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000

Dimensions in Inches

(for reference only)

Dimensions in Millimeters

(controlling dimensions)

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.

0° TO 8°

123

0.020

0.013

0.0040 MIN.

Dwg. MA-008-28A in

0.050

BSC

28 15 0.0125

0.0091

0.050

0.016

0.2992

0.2914 0.419

0.394

0.7125

0.6969

0.0926

0.1043

0°

8°

2318.10

17.70

0.51

0.33

2.65

2.35

0.10

MIN.

0.32

0.23

1.27

0.40

Dwg. MA-008-28A mm

1.27

BSC

7.60

7.40 10.65

10.00