L6243DS ,VOICE COIL MOTOR DRIVERFUNCTIONAL DESCRIPTION BLOCK DESCRIPTIONThe VCM Driver is controlled via two control sig- OUTPUT ST ..
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L6243DS
VOICE COIL MOTOR DRIVER
L6243DSVOICE COIL MOTOR DRIVER
5-12V OPERATION
PARKING FUNCTION FOR HARD DISK
HEAD ACTUATOR
OUTPUT CURRENT UP TO 1A DC, 1.2A
PEAK
LOW SATURATION VOLTAGE
LOGIC AND POWER SUPPLY MONITOR
LINEAR CONTROL
THERMAL PROTECTION
ENABLE FUNCTION
CURRENT SENSE RESISTOR CONNEC-
TIONS
DESCRIPTIONThe L6243DS is a Bipolar IC developed for use in
Mass Storage Head Actuator positioning applica-
tions. The Power Op-Amp Output Bridge, Differ-
ential Amplifier, and Error Amplifier, are control-
led by TTL/CMOS, input compatible, Digital Logic,
and an Analog Current Control Voltage.
A simple RC compensation network, tied to the
output of the Error Amp, will configure the system
to work as a Transconductance Amplifier to drive
a Voice Coil Motor in Linear Mode.
Additional features include Power On Reset De-
lay, Enable and Park. A logic low at the Park input
activates the parking function. Holding the Enable
input low will disable the device by forcing the
outputs into a tristate mode. Power Fail Monitors
for the logic and power supplies initiate an auto-
matic parking sequence during a power failure. A
resistor programmed parking voltage enables a
constant velocity head retract.
BLOCK DIAGRAM
ABSOLUTE MAXIMUM RATINGS
PIN FUNCTIONS
PIN CONNECTION (Top view)
L6243DS
THERMAL DATA
ELECTRICAL CHARACTERISTICS (VS = 12V, Tamb = 25°C; unless otherwise specified)ERROR AMPLIFIER
SENSE AMPLIFIER
POWER OP. AMP.
L6243DS3/8
FUNCTIONAL DESCRIPTIONThe VCM Driver is controlled via two control sig-
nals, ENABLE, POWER ON RESET. An analog
input voltage, ERROR AMP IN, controls the polar-
ity 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.
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
BLOCK DESCRIPTIONOUTPUT 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 output
when such a supply drops below the safe operat-
ing limit. After the logic supply voltage reaches its
nominal value a delay capacitor has to be
charged [Tdelay = 3x2x10e5 x C sec] before
Power on Reset output change from low to high
level. Falling edges of Power on Reset are de-
layed (typ 4μs) in order to disable the writing on
the disk before the Power on Reset is activated.
An additional supervisor circuit is present in the
ELECTRICAL CHARACTERISTICS (continued)MONITORS AND CONTROL CIRCUIT
L6243DS
IC with a programmable threshold, which is set
by an external resistive divider. The TTL compat-
ible output can be used separately or connected
to Park input in order to park the head.
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=100μA 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.
FUNCTIONAL DESCRIPTION (continued)
L6243DS5/8
Figure 1: Application Circuit
Figure 2: Application Circuit
L6243DS
