SP4427 Datasheet, PDF (3/9 Pages) Sipex Corporation – Electroluminescent Lamp Driver Dual Oscillators with High Drive Capability

PIN DESCRIPTION
1
8
2
7
3
6
4
5
Pin 1 – Cosc- Connect Cap1 from Vss to pin 1 to
set oscillator frequency.
Pin 2 – Vss- Power supply common, connect to
ground.
Pin 3 – Coil- Coil input, connect coil from
Vbattery to pin 3.
Pin 4 – EL2- Lamp driver output1, connect to
EL lamp.
Pin 5 – EL1- Lamp driver output2, connect to
EL lamp.
Pin 6 – Vdd- Power supply for driver, connect to
system Vdd.
Pin 7 – HON- Enable for driver operation,
high = active; low = inactive.
Pin 8 – Losc- Connect Cap2 from Vss to pin 8 to
set lamp frequency.
THEORY OF OPERATION
The SP4427 is made up of three basic circuit
elements: an oscillator, coil, and switched H-bridge
network. The oscillator portion of the circuit is
divided into two precision oscillators. The
oscillators set the coil and lamp frequencies
independently. This allows for the arbitrary setting
of the coil/lamp frequency ratio. The coil frequency
can be selected for maximum energy transfer per
cycle for a given external coil value. The coil
oscillator is set at 75% duty cycle and the lamp
oscillator is set at 50% duty cycle for minimum DC
offset across the EL lamp.
An external capacitor connected between pin 8
and V_SS allows the user to vary the lamp oscillator
frequency from 75Hz to 350Hz. Likewise, an
external capacitor connected between pin 1 and
V_SS allows the user to vary the coil oscillator
frequency from 3.5kHz to 50kHz. The graphs on
page 6 show the relationship between oscillators
(L_OSC and C_OSC) and their respective capacitor
values.
The coil is an external component connected from
V_battery to pin 3 of the SP4427. Energy is developed
in the coil according to the equation E =1/2LI²
L
where the current I is defined as I = (V_battery-IR-
V )/R . In order to maximize the energy produced
OL T
by the coil V_battery should represent the largest
Place as close
as possible to
IC pin 6
Vbat
+
0.1µF
Low
6
ESR CAP
1
200 pF
OSC 1
Coil
3
5
EL
DRIVER
OSC 2
4
1800 pF
8 _Lamp
2
HON
7
SP4427
Vbat
+
L1
20 mH/70Ω
EL Lamp
SP4427 Schematic
SP4427DS/01
SP4427 Electroluminescent Lamp Driver
3
© Copyright 1997 Sipex Corporation