SP4438 datasheet(9/19 Pages) SIPEX

9 / 19 page

Rev.11/13/00

SP4438 Ultra-Quiet Electroluminescent Lamp Driver

Audio Noise Considerations: A system

can have different sources of audio noise. The

coil, the filter capacitor, and the EL lamp itself

may be a source of audio noise if operated in the

audio frequency range.

Designers should select either the coil or coil

frequency such that the coil is not in continous

mode as this will greatly decrease efficiency and

contribute to noise.

Close attention should be given to the mounting

of the filter capacitor where the mounting can

act as an amplifier, such as in a speaker box.

Film capacitors do not exhibit audio noise

concerns but certain ceramic capacitors subjected

to a high voltage source can exhibit a

piezoelectric effect. This can be a source of

concern in the audio range.

The EL lamp itself can also exhibit audible noise

as a result of high voltage swings at frequencies

within the audio range. Close attention should

be given to the physical mounting of the EL

lamp to diminish this concern that can generate

both EMI and audio noise.

Electromagnetic

Interference (EMI)

Considerations: Electromagnetic Interferenc

Electromagnetic Interference (EMI) concerns

are rooted in uncontrolled high voltage swings

on the EL lamp. The controlled charging and

dischanging of the EL lamp by the SP4438

minimizes EMI effects.

Printed

Circuit

Board

Layout

Suggestions:

The SP4438's high voltage

operation makes PC layout important for

minimizing ground bounce and noise. Keep the

IC's GND pin and the ground leads of C1 and

INT less than 0.2 in (5mm) apart. Also keep the

connections to COIL as short as possible. To

maximize output power and efficiency and

minimize output ripple voltage, use a ground

plane and solder the IC's V

SS directly to the

ground plane.

EL Lamp Driver Design Challenges

There are many variables which can be optimized

for specific applications. The amount of light

emitted is a function of the voltage applied to the

lamp, the frequency at which it is applied, the

lamp material and the lamp size. Sipex supplies

characterization charts to aid the designer in

selecting the optimum circuit configuration.

Sipex will perform customer application

evaluations, using the customer's actual EL lamp

to determine the optimum operating conditions

for specific applications.

For customers

considering an EL backlighting solution for the

first time, Sipex is able to offer retrofitted

solutions to the customer's existing LED or non-

backlit product for a thorough electrical and

cosmetic evaluation. Refer to Figure 6 for an

enlargement and actual size evaluation board

layout.

Please contact your local Sales

Representative for Sipex or the Sipex factory

directly to initiate this valued service.

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