SP4424 Datasheet, PDF (3/12 Pages) Sipex Corporation – Electroluminescent Lamp Driver Dual Oscillators

PIN DESCRIPTION
1
8
2
7
3
6
4
5
Pin 1 – C - Connect Capacitor from V to
COIL
SS
pin 1 to set coil frequency.
Pin 2 – V_SS- Power supply common, connect to
ground.
Pin 3 – Coil- Coil input, connect coil from
V
to pin 3.
BATTERY
Pin 4 – EL1- Lamp driver output 1, connect to
EL lamp.
Pin 5 – EL2- Lamp driver output 2, connect to
EL lamp.
Pin 6 – V - Power supply for driver, connect to
DD
system V_DD.
Pin 7 – HON- Enable for driver operation,
high = active; low = inactive.
Pin 8 – C_LAMP- connect Capacitor from V_SS to
pin 8 to set lamp frequency.
THEORY OF OPERATION
The SP4424 is made up of four basic circuit
elements: two precision oscillators, a coil, and the
EL driver IC. The oscillators set the coil and lamp
frequencies independently. This allows for the
selective setting of the coil / lamp frequency ratio.
The coil frequency can be selected for maximum
energy transfer per cycle for a given coil value.
The coil oscillator is designed to operate at 75%
duty cycle and the lamp oscillator is designed for
50% DC, for minimum DC offset across the EL
lamp.
An external capacitor connected between pin 8
and V allows the user to vary the lamp oscillator
SS
frequency from approximately 75Hz (4700 pf) to
350Hz (450 pf). Likewise, an external capacitor
connected between pin 1 and V allows the user
SS
to vary the coil oscillator frequency from
approximately 5kHz (390 pf) to 50kHz (22 pf).
The graphs on page 7 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 SP4424. Energy is stored
in the coil according to the equation E_L=1/2LI²,
where I is the peak current flowing in the inductor.
The current in the inductor is time dependent and
is set by the "ON" time of the coil switch: I=(V /
L
L)t , where V is the voltage across the inductor.
ON
L
At the moment the switch closes, the current in the
inductor is zero and the entire supply voltage
(minus the V of the switch) is across the inductor.
SAT
The current in the inductor will then ramp up at a
V_IN=3V ₊
–
220pF
SP4424 Typical Application
SP4424DS/16
C_COIL
V_SS
Coil
EL1
C_LAMP
HON
V_DD
EL2
SP4424
1500pF
HON=V_DD=ON
HON=0V=OFF
0.1µF Low ESR
Decoupling
Capacitor
EL Lamp 3Ftl
1.6 sq.in.
4.5nF
SP4424 Electroluminescent Lamp Driver
3
© Copyright 2000 Sipex Corporation