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| SP4428 Datasheet, PDF (3/11 Pages) Sipex Corporation – Electroluminescent Lamp Driver High Drive Capability for Low Voltage Applications | |||
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PIN DESCRIPTION
1
8
2
7
3
6
4
5
Pin 1 â COSC- Connect CAP from VSS to Pin 1 to
set Oscillator frequency.
Pin 2 â V - Power supply common, connect to
SS
ground.
Pin 3 â Coil- Coil input, connect coil from
V
to Pin 3.
BATTERY
Pin 4 â D1- Diode cathode connection.
Pin 5 â EL2- Lamp driver output1, connect to
EL lamp.
Pin 6 â EL1- Lamp driver output2, connect to
EL lamp.
Pin 7 â VDD- Power supply for driver, connect to
system VDD.
Pin 8 â HON- Enable for driver operation,
high = active; low = inactive.
THEORY OF OPERATION
The SP4428 is made up of three basic circuit
elements, an oscillator, coil, driver and switched
H-bridge network. The oscillator provides the
device with an on-chip clock source used to control
the charge and discharge phases for the coil and
lamp. An external capacitor connected between
pins 1 and VSS allows the user to vary the oscillator
frequency. For a given choice of coil inductance
there will be an optimum COSC Capacitor value that
gives the maximum light output in a given lamp.
The suggested oscillator frequency is 28.8kHz
(COSC=180pF). The oscillator output is internally
divided to create the control signal fLAMP.
The oscillator output is internally divided down
by 6 flip flops, a 28.8kHz signal will be divided
into 6 frequency levels; 14.4kHz, 7.2kHz, 3.6kHz,
1.8kHz, 900Hz, and 450Hz. The oscillator output
(28.8kHz) is used to drive the coil (see figure 2 on
page 7) and the sixth flip flop output (300Hz) is
used to drive the lamp. Although the oscillator
frequency can be varied to optimize the lamp
output, the ratio of fCOIL/fLAMP will always equal 64.
The coil is an external component connected from
VBATTERY to pin 3 of the SP4428. Energy is
developed in the coil according to the equation
EL=1/2LI2 where the current I is defined as
I=(VBATTERY-IR-VOL)/RT. In order to maximize the
.1µF
VDD
7
VDD
180pF
1 COSC
OSC
Cap1
FF1
SP4428 Schematic
SP4428DS/16
1Mâ¦
8
HON
VBATTERY
470µH/4.9â¦
IN4148
3
Coil
fCOIL
SCR1
Optional
1,800pF
4
D1
SCR2
Q
FF6
Q
VSS
2
fLAMP
fLAMP
EL Lamp
EL1
5
EL2
6
SP4428 Electroluminescent Lamp Driver
3
© Copyright 2000 Sipex Corporation
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