BLOCK DESCRIPTION

OUTPUT STAGE

It consists of two Power Op Amps connected in

bridge configuration.

CURRENT SENSE AMPLIFIER

Differential amplifier whose inputs are connected

to the sense lines and whose output is accessible

externally. Closing the loop will transform the

differential voltage signal from the sense lines into

a current signal for the Error Amplifier.

ERROR AMPLIFIER

Error amplifier which drives the output stage. The

input and the output pins are accessible exter-

nally.

POWER SUPPLY MONITOR OPERATION

The circuit monitors the logic supply voltage input

(typ 5V) and activates Power on Reset and Write

Disable output when such a supply drops below

the safe operating limit. After the logic supply volt-

age reaches its nominal value a delay capacitor

has to be charged [Tdelay=3x10e5 x C sec] be-

fore Power on Reset and Write Disable outputs

change from low to high level. Falling edges of

Write Disable and Power on Reset are delayed

(typ 4

µs) in order to disable the writing on the disk

before the Power on Reset is activated. An addi-

tional supervisor circuit is present in the IC with a

programmable threshold, which is set by an exter-

nal resistive divider. The TTL compatible output

can be used separately or connected to Park in-

put in order to park the head.

to 5V filter input in order to implement a POWER

PARKING CIRCUIT OPERATIONT

The voice coil driver is switched into the parking

condition when Power on Reset output or Park in-

put are low. In such a condition a fixed voltage is

superimposed on the load and the value of such a

voltage is set by connecting an external resistor

between

Park

Voltage

Program

input

and

ground: (Vpark=Rext x Iref, Iref=100

µA typ). Con-

necting ENABLE input to GND the driver will be

disabled (outputs in high impedance mode).

THERMAL SHUTDOWN

It will disable the IC when the junction tempera-

ture exceeds the threshold value above which the

device could be damaged.

Figure 1: Application Circuit (The pinout refers to the L6243)

L6243-L6243D

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