SP4422A Datasheet, PDF (3/13 Pages) Sipex Corporation – Electroluminescent Lamp Driver

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 SP4422A 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_OSC and lamp
output voltage. In general, increasing the C_OSC
capacitor will increase the lamp output.
The suggested oscillator frequency is 90kHz
(C_OSC=100pF). 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 90kHz signal will be
divided into 8 frequencies; 45kHz, 22.5kHz,
11.2kHz, 5.6kHz, 2.8kHz, 1.4kHz, 703Hz, and
352Hz. The third flip flop output (8kHz) is used to
drive the coil (see figure 2 on page 9) and the
eighth 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.
The on-chip oscillator of the SP4422A can be
overdriven with an external clock source by
removing the C_OSC capacitor and connecting a
0.1µF
V_DD
6
V_DD
1
HON
V_BATTERY
5mH/18Ω
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
SP4422A Schematic
SP4422ADS/15
SP4422A Electroluminescent Lamp Driver
3
© Copyright 2000 Sipex Corporation