SP4424 Datasheet, PDF (5/12 Pages) Sipex Corporation – Electroluminescent Lamp Driver Dual Oscillators

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
V_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.
SP4424DS/16
SP4424 Electroluminescent Lamp Driver
5
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