SP4425Q Datasheet, PDF (3/12 Pages) Sipex Corporation – Electroluminescent Lamp Driver for Low Noise Applications

PIN DESCRIPTION
1
8
2
7
3
6
4
5
Pin 1 – C_OSC- Capacitor input 1, connect Capacitor
from V_SS to Pin 1 to set C_OSC frequency.
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 – D1- Diode Cathode connection.
– C_INT- Integrator capacitor, connect capacitor
from pin 4 to ground to minimize coil glitch energy.
Pin 5 – Lamp- Lamp driver output2, connect to
EL lamp.
Pin 6 – Lamp- Lamp driver output1, connect to
EL lamp.
Pin 7 – V_DD- Power supply for driver, connect to
system V_DD.
Pin 8 – HON- Enable for driver operation,
high = active; low = inactive.
THEORY OF OPERATION
The SP4425Q 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 1 and
Vss allows the user to vary the oscillator frequency.
For a given choice of coil inductance there will be
an optimum C_OSC capacitor value that provides
maximum light output.
The suggested oscillator frequency is 28.8kHz
(C_OSC=180pF). The oscillator output is internally
divided to create the control signal for f_LAMP. 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, 900kHz, and 450Hz. The oscillator output
(28.8kHz) is used to drive the coil (see figure 2 on
page 6) 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 f_COIL/f_LAMP will always equal 64.
The coil is an external component connected from
V_BATTERY to pin 3 of the SP4425Q. V_BATTERY= 3.0
VDC with a 2mH/44Ω coil are typical conditions.
Energy is stored in the coil according to the equation
Low ESR
V_DD
decoupling
capacitor
.1µF
7
V_DD
180pF
1 C_OSC
OSC
Cap1
FF1
SP4425Q Schematic
SP4425QDS/12
1MΩ
8
HON
V_BATTERY
2mH/44Ω
IN4148
3
Coil
f_COIL
SCR1
C_INT = 820pF typical
4
D1
SCR2
Q
FF6
Q
V_SS
2
f_LAMP
f_LAMP
EL2
EL1
5
6
QR2
QR1
EL Lamp
SP4425Q Electroluminescent Lamp Driver
3
© Copyright 1998 Sipex Corporation