8904

3-PHASE BRUSHLESS DC

MOTOR CONTROLLER/DRIVER

www.allegromicro.com

7

Terminal Functions

A8904SLB

A8904SLP

Terminal Name

Function

(SOIC)

(HTSSOP)

LOAD SUPPLY

V

1

15

C

D2

One of two capacitors used to generate the ideal commutation points from

2

16

the back-EMF zero crossing points.

C

WD

Timing capacitor used by the watchdog circuit to blank out the back-EMF

3

17

comparators during commutation transients, and to detect incorrect motor

position.

C

ST

Startup oscillator timing capacitor.

4

18

NC

No( internal) connection.

–

19

OUT

A

Power amplifier A output to motor.

5

20

NC

No (internal) connection.

–

21

GROUND

Power and logic ground and thermal heat sink.

6-7

–

POWER GROUND

Power ground.

–

22*

NC

No (internal) connection.

–

23

OUT

B

Power amplifier B output to motor.

8

24

OUT

C

Power amplifier C output to motor.

9

25

CENTERTAP

Motor centertap connection for back-EMF detection circuitry.

10

26

BRAKE

Active low turns ON all three sink drivers shorting the motor windings to

11

27

The brake function can also be controlled via the serial port.

C

RES

External reservoir capacitor used to hold charge to drive the source drivers’

12

28

gates. Also provides power for brake circuit.

ANALOG GROUND

Analog ground.

–

1*

FILTER

Analog voltage input/output to control motor current. Also, compensation node

for internal speed control loop.

13

2

SECTOR DATA

External tachometer input. Can use sector or index pulses from disk to

14

3

provide precise motor speed feedback to internal frequency-locked loop.

LOGIC SUPPLY

V

15

4

OSCILLATOR

Clock input for the speed reference counter.

16

5

DATA OUT

Thermal shutdown indicator, FCOM, TACH, or SYNC signals available in

17

6

real time, controlled by 2-bit multiplexer via serial port.

NC

No (internal) connection.

–

7

GROUND

Power and logic ground and thermal heat sink.

18-19

–

DIGITAL GROUND

Logic ground.

–8*

RESET

When pulled low forces the chip into sleep mode; clears all serial port bits.

20

9

NC

No (internal) connection.

–

10

CHIP SELECT

Strobe input (active low) for data word.

21

11

CLOCK

Clock input for serial port.

22

12

DATA IN

Sequential data input for the serial port.

23

13

C

D1

One of two capacitors used to generate the ideal commutation points from

24

14

the back-EMF zero crossing points.

* For the A8904SLP, ground terminals 1, 8, and 22 must be connected together externally.