Datasheet A8936CLW, A8936CJT Datasheet (Allegro)

8936

INTERIM DATA SHEET

VOICE COIL MOTOR DRIVER

(Subject to change without notice)
March 16, 1993

8936

Data Sheet

26300.6

VOICE COIL MOTOR DRIVER

A8936CLW

1

RET REF

V

2

V

BEMF

GROUND

UV

R

OUT P

OUT

EN VEL FLT

IN

VEL

RETRACT

FAULT

MP

RESET

SIGNAL

SUPPLY

FLT

PROTECT

CIRCUIT

3

4

5

SET

6

V

+

PROTECT

CIRCUIT

V

CC

REF

–

7

8

9

N

10

IN

11

12

13

14 15

WINDOW

COMP.

V

REF

R

Q

S

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,

V

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

IN

Package Power Dissipation,

P

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

D

(peak) .......... ±600 mA

OUT

RET SET

28

27

V

SENS

VEL FLT

26

V

25

SENS FB

24

SGND

N

OUT

23

P

LOAD

22

V

DD

SUPPLY

21

OUT

N

SGND

20

P

ACT

19

FB

18

PWR OFF

H GAIN

17

16

REFERENCE

+

–

ACT

Dwg. PP-046A

CC

Providing control and drive of the voice coil motor used for head
positioning in 5 V disk drive applications, the A8936C— is a full-bridge
driver which 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. An under- or over-velocity sense disables the
system in a controlled sequence if a fault condition occurs.

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. Thermal protection and under-voltage
lockout disables the system in a controlled sequence if a fault condi­tion occurs.

FEATURES

■ Over-Velocity Fault Function

■ Lossless Current Sensing

■ Zero 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

■ Chip Enable/Sleep Mode Function

■ 1 V at 500 mA Output Saturation Voltage

■ Internal Thermal Shutdown Circuitry

Operating Temperature Range,

T

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

A

Junction Temperature, T

.............. +150°C

J

†

Storage Temperature Range,

T

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

S

DISCONTINUED PRODUCT

† 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

— FOR REFERENCE ONLY

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:

Part Number Package
A8936CJT 64-Lead Thin Quad Flatpack
A8936CLW 28-Lead SOIC

A

TM

TM

MicroSystems, Inc.

8936

VOICE COIL MOTOR DRIVER

FUNCTIONAL BLOCK DIAGRAM

= 'LW' WIDE-BODY SOIC
= 'JT' THIN QUAD FLATPACK

19

FB

1

15

55

16

58

60

17

18

62

12

50

13

51

ACT

ACT

REFERENCE

H GAIN

PWR OFF

FAULT

MP

RESET

SIGNAL

SUPPLY

14 22

V

CC

I

SENSE +

ERROR

AMP

–

2 V

+

–

+

POWER

CONTROL

LOGIC

TSD

PROTECTION

CIRCUITRY

33

28 27 23 25 47 34

53 2 281 611 4

SET

BEMF

UV

V

V

FLT

RETRACT
CONTROL

RET REF

RET SET

POWER

AMP

I

SENSE –

RETRACT

LOAD

SUPPLY

853

V

DD

19
26

OUT P

R

V

REF

CURRENT-SENSE
AMP

V

REF

S

Q

R

Q

VEL FLT

+

–

–

+

WINDOW

COMP.

30

GROUND

35

45

2

13

4

15

16

21

46

V

REF

36

7

OUT

9

IN

20

SGND

23

OUT

21

OUT

24

SGND

25

V

27

V

10

VEL

8

EN VEL FLT

Dwg. FP-030A

N

P

P

N

N

SENS FB

SENS

IN

2.0

1.5

FREE AIR,

R = 66°C/W

θJA

1.0

0.5

0

25

ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS

A

50 75 100 125 150

AMBIENT TEMPERATURE IN °C

Dwg. GP-034

TM

TM

MicroSystems, Inc.

115 Northeast Cutoff, Box 15036
115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 [phone]
Worcester, Massachusetts 01615-0036 [phone]

Copyright © 1992, 1993, Allegro MicroSystems, Inc.

A8936CJT

V

PROTECT.

CIRCUIT

CC

PROTECT.

CIRCUIT

V

REF

+ —

Dwg. PP-052-1

+

—

V

DD

V

REF

WINDOW

COMP.

S R
Q

RETRACT
CONTROL

8936

VOICE COIL MOTOR DRIVER

ELECTRICAL CHARACTERISTICS at T

= +25°C, VCC = VDD = 5.0 V, V

A

= VIN= 2.0 V,

REF

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

IO

iH

A

iL

L(adj)

REF

Current-Sense Amplifier

Voltage Gain A
Input Offset Voltage V

VD

iO

Output Drivers

Output Saturation Voltage V

DS(SAT)

(Source + Sink)

Retract Output Saturation Voltage V
Output Current I

DS(SAT)

O

Full Power Bandwidth BW -3 dB 1.0 —— kHz

Window Comparator

Lower Trip Point VEL
Upper Trip Point VEL

IN

IN

Uncommitted Op Amp

Voltage Gain A

VS

Unity Gain Bandwidth BW — 1.0 — MHz
Max. Load Capacitance C

LOAD

Slew Rate SR — 4.2 — V/µs
Output Voltage V
Max. Output Current I
Input Offset Voltage V

O

O

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

= 5 mA to 500 mA, Ai = A

I

OUT

iL
iH

——±10 %
——±10 %

1.5 — 2.5 V

Rs = R

gm

I

= 0 mA, Ai = A

LOAD

I

= 100 mA — 0.25 — V

LOAD

I

= 500 mA — 1.5 — V

LOAD

I

≤ 150 mA ——1.0 V

OUT

iL

— 1.0 ——
——±25 mV

Pulse Test, ±600 mA Limited ——±500 mA

1.12 1.25 1.38 V

2.47 2.75 3.03 V

— 91 — dB

40 —— pF

VIO = 100 mV 2.5 — 3.5 V

— ±250 — µA
——±10 mV

Negative current is defined as coming out of (sourcing) the specified device terminal.
Typical Data is for design information only.

Continued next page …

8936

VOICE COIL MOTOR DRIVER

ELECTRICAL CHARACTERISTICS at T

= +25°C, VCC = VDD = 5.0 V, V

A

= VIN= 2.0 V,

REF

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

Limits

Characteristic Symbol Test Conditions Min. Typ. Max. Units
Miscellaneous

Under-Voltage Lockout Voltage V
Fault Logic Output V

Power-On Reset V

Total Supply Current I

Logic Input Voltage V

Thermal Shutdown Temperature T
Thermal Shutdown Hysteresis ∆T

Negative current is defined as coming out of (sourcing) the specified device terminal.
Typical Data is for design information only.

CC

FAULT

I

FAULT

MPRESET

+ I

CC

DD

IN(0)

V

IN(1)

J

J

VCC = V
V
V
V
V
V
Outputs Balanced, No Load ——10 mA
Sleep Mode, PWR OFF = 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

MPRESET

CC

3.9 4.2 4.35 V

——2.0 mA
——0.7 V

3.5 —— V
— 165 — °C
— 20 — °C

A

TM

TM

MicroSystems, Inc.

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

8936

VOICE COIL MOTOR DRIVER

TERMINAL FUNCTIONS

"JT" Term."LW" Term. Term. Name Function

25 1 RET REF The reference supply for setting the voltage across the load during retract.
27 2 V
28 3 V

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.
30 4 GROUND Circuit reference.
33 5 UV

SET

Under-voltage trip point reference input. Set internally to 4.3 V but may be over-ridden by external

resistor divider. (Equation 4).
34 6 R

OUT P

Source driver used for retract; externally connected to OUTP.
35 7 OUT Output of uncommitted operational amplifier.
36 8 EN VEL FLT Logic input for over-velocity fault latch.
45 9 IN
46 10 VEL

N

Inverting input to uncommitted operational amplifier.

Analog voltage input corresponding to motor speed.

IN

47 11 RETRACT An active-low logic input that initiates the retract sequence.
50 12 FAULT A logic low at this MOS output indicates a thermal shutdown, under-voltage fault, or retract command.
51 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.
53 14 SIGNAL SUPPLY VCC; low-current supply voltage in the range of 4.5 V to 5.5 V.
55 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).
58 16 REFERENCE V

; reference input for all amplifiers; ac ground.

REF

60 17 H GAIN Logic input to switch the error amplifier transconductance gain: LOW = 2100, HIGH = 8400.
62 18 PWR OFF An active-high logic input that puts the device in a “sleep mode”. All fault circuitry remains active.
1 19 ACT
2 20 SGND
4 21 OUT

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

FB

Power ground for the OUTP sink driver.

P

Power output. Sinks current when V

N

ACT

< V

REF

.
8 22 LOAD SUPPLY VDD; high-current supply voltage for the voice-coil motor.
13 23 OUT
15 24 SGND
16 25 V

SENS FB

Power output. Sinks current when V

P

Power ground for the OUTN sink driver.

N

ACT

> V

REF

.

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

Also called gm SET.
19 26 VEL FLT An active-low logic output indicating an over-velocity fault.
21 27 V

SENS

Voltage output representing load current (Equation 2). Also called MONITOR.
23 28 RET SET An external resistor divider to set the retract voltage across the load.

Used in conjunction with V

RET-REF

(Equation 3).

8936

VOICE COIL MOTOR DRIVER

DEVICE DESCRIPTION

Current Amplifier. The A8936CJT and A8936CLW
voice coil motor drivers feature a wide transconductance
bandwidth and no measurable crossover distortion. The
transconductance gain is user selectable:

A

gm =

i

R

gm

(Equation 1)

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. Two 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:

RS I

V

SENS

=

A

LOAD

iL

(Equation 2)

The second auxiliary amplifier 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.

Under- & Over-Velocity Fault. For a constant load,
motor current (I
to motor velocity. V

) and therefore V

LOAD

is amplified by the uncommitted

SENS

are proportional

SENS

amplifier and compared against the internal 2 V refer­ence and used to indicate a velocity fault if the voltage is
greater than a nominal ±0.75 V from the 2 V reference.
EN VEL FLT may be tied to the FAULT terminal to reset
the velocity fault after a tripout.

Retract and Brake. A retract-brake sequence is initiated
on receiving a fault indication from the internal thermal
shutdown (TSD), under-voltage lockout (UVLO), the
under- or over-velocity fault, 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 INPUT 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 R

V

RET-SET

=

1000 + R7 + R

8

8

(Equation 3)

where R7 + R8 >> 1000 Ω.

When the sequence is operated, the output voltage is
forced to approximately V

to retract the heads, and

RET-SET

then a fault command (“brake”) is sent to the spindle­motor 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
V

terminal. The A8936CJT/CLW will perform the

BEMF

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 A8936CJT/CLW 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 under­voltage trip point is internally set at approximately 4.3 V.
It can be user-defined with an external resistor voltage
divider:

2 (R5 + R6)

UV

=

TRIP

R

6

(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.

A

TM

TM

MicroSystems, Inc.

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

8936

VOICE COIL MOTOR DRIVER

TEST CIRCUIT AND TYPICAL APPLICATION

2 V

V

CC

I

SENSE +

+

–

R

Z

C

R

V

IN

gm

V = 2 V

Z

REF

H GAIN

ERROR

–

+

AMP

POWER

AMP

+5 V

V

V

DD

REF

+

–

–

C

1

R

VOICE COIL

MOTOR

1

PWR OFF

R ≥ 200 kΩ

FAULT

V

CC

BACK EMF FROM
SPINDLE MOTOR

PROTECTION

CIRCUITRY

R

5

R

6

POWER

CONTROL

LOGIC

TSD

RETRACT

CONTROL

R

7

R

8

V

DD

CURRENT-SENSE

I

SENSE –

RETRACT

DIODE FOR RETRACT FUNCTION
OTHERWISE SHORT TO SUPPLY

AMP

Q
Q

VEL FLT

V

REF

S
R

–

+

WINDOW

COMP.

R

S

V

SENS

V

REF

Dwg. EP-043A

8936

VOICE COIL MOTOR DRIVER

A8936CJT

Dimensions in Inches

(Based on 1 mm = 0.03937”)

0.0039

±0.0024

0.018

0.030

0.0035

0.0079

0.050

0.065

0.472

BSC

0.394

BSC

49

0.005

0.017

0.0197

BSC

64

48

EJECTOR
MARK

INDEX
MARK

1

0.472

BSC

0.394

BSC

33

32

17

16

Dwg. MA-004 in

NOTES: 1. This device is similar to JEDEC registration MO-136BJ except for certain tolerances. Contact factory for detailed information.

2. Lead spacing tolerance is non-cumulative.

3. Exact body and lead configuration at vendor’s option within limits shown.

4. The top package body size may be smaller than the bottom package body size by as much as 0.006”.
Body dimensions include mold mismatch but do not include mold protrusion.

TM

TM

115 Northeast Cutoff, Box 15036

A

MicroSystems, Inc.

Worcester, Massachusetts 01615-0036 [phone]

8936

VOICE COIL MOTOR DRIVER

A8936CJT

Dimensions in Millimeters

0.10

±0.06

0.30

0.75

0.09

0.20

1.29

1.65

12.0

BSC

10.0

BSC

0.14

0.27

0.50

BSC

48

49

EJECTOR
MARK

INDEX
MARK

64

1

10.0

BSC

12.0

BSC

33

32

17

16

Dwg. MA-004 mm

NOTES: 1. This device is similar to JEDEC registration MO-136BJ except for certain tolerances. Contact factory for detailed information.

2. Lead spacing tolerance is non-cumulative.

3. Exact body and lead configuration at vendor’s option within limits shown.

4. The top package body size may be smaller than the bottom package body size by as much as 0.15 mm.
Body dimensions include mold mismatch but do not include mold protrusion.

8936

VOICE COIL MOTOR DRIVER

A8936CLW

DIMENSIONS IN INCHES

(Based on 1 mm = 0.03937")

28 15

0.0125

0.0091

0.2992

0.2914

0.020

0.013

0.0926

0.1043

7.60

7.40

2

1

0.0040 MIN.

DIMENSIONS IN MILLIMETERS

28

3

0.7125

0.6969

15

0.050
BSC

0.491

0.394

0.050

0.016

0° TO 8°

Dwg. MA-008-28 in

0.32

0.23

10.65

10.00

1.27

0.40

0.51

0.33

2.65

2.35

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 design of its products. Components made under military
approvals will be in accordance with the approval requirements.

The information included herein is believed to be accurate and reliable.
However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for
any infringements of patents or other rights of third parties which may result from
its use.

A

MicroSystems, Inc.

2

1

0.010 MIN.

TM

TM

3

18.10

17.70

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

1.27
BSC

NOTES: 1. Lead spacing tolerance is non-cumulative.

2. Exact body and lead configuration at vendor’s option
within limits shown.

0° TO 8°

Dwg. MA-008-28 mm