SP4423 Datasheet, PDF (3/13 Pages) Sipex Corporation – Electroluminescent Lamp Driver Low Power Applications

PIN DESCRIPTION
1
8
2
7
3
6
4
5
Pin 1 – HON- Enable for driver operation,
high = active; low = inactive.
Pin 2 – V - Power supply common, connect to
SS
ground.
Pin 3 – Coil- Coil input, connect coil from V
DD
to pin 3.
Pin 4 – Lamp- Lamp driver output2, connect to
EL lamp.
Pin 5 – Lamp- Lamp driver output1, connect to
EL lamp.
Pin 6 – V_DD- Power supply for driver, connect to
system V_DD.
Pin 7 – Cap1- Capacitor input 1, connect to C .
OSC
Pin 8 – Cap2- Capacitor input 2, connect to C_OSC.
THEORY OF OPERATION
The SP4423 is made up of three basic circuit
elements, an oscillator, coil, 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 7 and 8 allows the user to vary the
oscillator frequency from 32kHz to 400kHz.
The graphs on page 6 show the relationship
between C and lamp output voltage.
OSC
In general, increasing the C_OSC capacitor will
increase the lamp output voltage and decrease
the lamp frequency.
The suggested oscillator frequency is 64kHz
(C_OSC=150pF). The oscillator output is internally
divided to create two internal control signals,
f_COIL and f_LAMP. The oscillator output is internally
divided down by 8 flip flops; a 64kHz signal
will be divided into 8 frequencies; 32, 16, 8, 4,
2, 1, 0.5, and 0.25 Hz. The 3rd flip flop output
(8kHz) is used to drive the coil (see Figure 2 on
page 9) and the 8th flip flop output (250Hz) is
used to drive the lamp. Although the oscillator
frequency can be varied to optimize the lamp
output, the ratio of f_COIL/f_LAMP will always
equal 32.
0.1µF
V_DD
6
V_DD
1
HON
V_BATTERY
20mH/70Ω
3
Coil
OSC
7
Cap1
Cap2
8
FF1
Q
FF2
Q
V_SS
2
f_COIL
f_LAMP
f_LAMP
SCR1
SCR2
EL2
EL1
4
5
EL Lamp
SP4423 Schematic
SP4423DS/14
SP4423Electroluminescent Lamp Driver
3
© Copyright 2000 Sipex Corporation