SP4438 Datasheet, PDF (9/19 Pages) Sipex Corporation – Ultra-Quiet Electroluminescent Lamp Driver For Cellular Phone Applications

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
C_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.
Rev.11/13/00
SP4438 Ultra-Quiet Electroluminescent Lamp Driver
9
© Copyright 2000 Sipex Corporation