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.

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.

Under-voltage trip point reference input. Set internally to 4.2 V but may be overridden by

external resistor divider. (Equation 4).

7

OUT

Output of uncommitted operational amplifier.

8

SWITCH

Inverting input to uncommitted operational amplifier.

10

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

(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

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

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

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

20

21

22

LOAD SUPPLY

23

24

25

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

bandwidth. Also called gm SET.

26

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

velocity control.

27

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

TERMINAL FUNCTIONS