SP4424CX datasheet(3/12 Pages) SIPEX

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SP4424DS/16

SP4424 Electroluminescent Lamp Driver

PIN DESCRIPTION

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

SS allows the user to vary the lamp oscillator

frequency from approximately 75Hz (4700 pf) to

350Hz (450 pf). Likewise, an external capacitor

connected between pin 1 and V

SS allows the user

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 COSC) and their respective

capacitor values.

The coil is an external component connected from

BATTERY to pin 3 of the SP4424. Energy is stored

in the coil according to the equation E

L=1/2LI

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)t

ON, where VL is the voltage across the inductor.

At the moment the switch closes, the current in the

inductor is zero and the entire supply voltage

(minus the V

SAT of the switch) is across the inductor.

The current in the inductor will then ramp up at a

Pin 1 – C

COIL- Connect Capacitor from VSS to

pin 1 to set coil frequency.

Pin 2 – V

SS- Power supply common, connect to

ground.

Pin 3 – Coil- Coil input, connect coil from

BATTERY to pin 3.

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

DD- Power supply for driver, connect to

system V

DD.

Pin 7 – HON- Enable for driver operation,

high = active; low = inactive.

Pin 8 – C

LAMP- connect Capacitor from VSS to

pin 8 to set lamp frequency.

SP4424 Typical Application

HON=VDD=ON

HON=0V=OFF

0.1

µF Low ESR

Decoupling

Capacitor

EL Lamp

3Ftl

1.6 sq.in.

4.5nF

CLAMP

HON

VDD

EL2

CCOIL

VSS

Coil

EL1

220pF

SP4424

VIN=3V

–

1500pF

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