FUNCTIONAL DESCRIPTION

The VCM Driver is controlled via three control sig-

nals, ENABLE, POWER ON RESET, and WRITE

DISABLE. An analog input voltage, ERROR AMP

IN, controls the polarity and amplitude of the VCM

driving current.

Refer to figure two. This diagram is a repre-

sentation of the function of the VCM System.

Note that the signals with the bars represent the

”not

true”, or ”non asserted” condition. From in -

itial power up, the system is held in the Park

Mode. Upon completion of the POWER UP RE-

SET DELAY the machine moves to Tristate Mode

or Run Mode, depending upon the condition of

the ENABLE input. If ENABLE is asserted, the

machine moves directly to Run Mode. If ENABLE

is not asserted, the machine moves to Tristate

Mode.

POWER ON RESET is an asynchronous output.

Additionally it affects the internal logic as a hard

wired reset and therefore if a supply failure occurs

during Tristate or Run state, the machine moves

directly back to the Park Mode. A WRITE DIS-

ABLE occurs a few to ten microseconds prior to

the POWER ON RESET in order for the system

to halt any read/write activity before a head re-

tract begins.

While in Tristate Mode, the assertion of ENABLE

will move the machine to the Run Mode. Run

Mode will typically be the steady running state.

The deassertion of the ENABLE signal causes

the machine to move into Tristate. If it is desired

to perform an active Parking function, the PARK

input must be driven low by the external hard-

ware, or the the VCM can be driven to the Park

position via the ERROR AMP IN control voltage

ELECTRICAL CHARACTERISTICS (continued)

MONITORS AND CONTROL CIRCUIT

Symbol

Parameter

Test Condition

Min.

Typ.

Max.

Unit

Threshold Voltage at Logic

Supply Sense

4.45

4.60

4.75

V

Threshold Voltage at Power Fail

Threshold Input

1.375

1.4

1.435

V

50

mV

Hysteresis on Vt2

15

mV

Low Level Voltage

Write Disable = 2mA

250

500

mV

Power on Reset = 2mA

250

500

mV

Enable Input Current

100

µA

–200

µA

Input Current at Park

100

µA

–200

µA

Equivalent Input Resistance at

5V Filter Input

6.9

K

Ω

Enable Low Input Voltage

0.8

V

Enable High Input Voltage

2

V

Parking Input High Voltage

2

V

Parking Input Low Voltage

0.8

V

Power Fail Low Output Voltage

0.5

V

Parking Voltage Program Current

100

µA

Power On Reset Delay

Capacitor Charging

10

µA

Delay Between Write Disable

and Power on Reset Falling

Edges

410

µs

L6243-L6243D

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