SP4424 datasheet(5/12 Pages) SIPEX

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SP4424DS/16

SP4424 Electroluminescent Lamp Driver

CIRCUIT LAYOUT CONSIDERATIONS:

The SP4424 IC incorporates two independent

asynchronous oscillators, one of which supplies

the signal for switching of the coil transistor which

generates the coil charge pulses and the other

supplies the clock signal to switch the high voltage

H-bridge output circuit.

It is necessary to keep all high voltage signals

away from these oscillator clock signals as much

as possible as crosstalk between the two signals

can cause distortion in the EL drive signal which

can result in either low light output or blinking of

the EL lamp. It is always recommended that a low

ESR decoupling capacitor (0.1

µF or >) be used

between the V

DD (pin 6) and ground (pin 2). The

SS (gnd) pin should in turn be connected to the

system ground plane. If it is connected via a

circuit trace, this trace should be as short and as

wide as possible.

Electroluminescent Technology

What is electroluminescence?

An EL lamp is basically a strip of plastic that is

coated with a phosphorous material which emits

light (fluoresces) when a high voltage (>40V)

which was first applied across it, is removed. Long

periods of DC voltages applied to the material

tend to breakdown the material and reduce its

lifetime. With these considerations in mind, the

ideal signal to drive an EL lamp is a high voltage

sine wave. Traditional approaches to achieving

this type of waveform included discrete circuits

incorporating a transformer, transistors, and several

resistors and capacitors. This approach is large,

power hungry, expensive and bulky, and would be

difficult to implemented in most hand held

equipment.

Sipex now offers low power single chip driver

circuits specifically designed to drive small to

medium sized electroluminescent panels. All that

is required is one external inductor and capacitor.

Electroluminescent backlighting is ideal for use

with LCD displays, keypads, or other backlit

readouts. Its primary use is to illuminate displays

in dim to dark conditions for momentary periods

of time. EL lamps typically consume less current

than LEDs or bulbs making them ideal for battery

powered products. Also, EL lamps are able to

evenly light an area without creating "hot spots" in

the display.

The amount of light emitted is a function of the

voltage level applied to the lamp, the frequency at

which it is applied and the lamp size and method of

construction . There are many variables which can

be optimized for specific applications. Sipex

supplies custom characterization data to aid the

designer in selecting the optimum circuit

configuration.

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