SP4422A Datasheet, PDF (5/13 Pages) Sipex Corporation – Electroluminescent Lamp Driver

When the energy from the coil is released, a high
voltage spike is created triggering the SCR
switches. The direction of current flow is
determined by which SCR is enabled. One full
cycle of the H-bridge will create 16 voltage steps
from ground to 80V (typical) on pins 4 and 5 which
are 180 degrees out of phase from each other (see
figure 3 on page 9. A differential representation of
the outputs is shown in figure 4 on page 9.
Layout Considerations
The SP4422A circuit board layout must observe
careful analog precautions. For applications with
noisy voltage power supplies a 0.1µF low ESR
decoupling capacitor must be connected from V_DD
to ground. Any high voltage traces should be
isolated from any digital clock traces or enable
lines. A solid ground plane connection is strongly
recommended. All traces to the coil or to the high
voltage outputs should be kept as short as possible
to minimize capacitive coupling to digital clock
lines and to reduce EMI emissions.
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 or
reversed. 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 and bulky, and cannot be 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 when used
with LCD displays, keypads, or other backlit
readouts. Its main use is to illuminate displays in
dim to dark conditions for momentary periods of
time. EL lamps typically consume less 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 applied to the lamp, the frequency at which
it is applied, the lamp material used and its size,
and lastly, the inductor used. There are many
variables which can be optimized for specific
applications. Sipex supplies characterization charts
to aid the designer in selecting the optimum circuit
configuration (see page 6).
HON=V_DD=ON
HON=0V=OFF
V_IN=3V ₊
–
NOTE:
Keep coil as close to the
SP4422A as possible
HON
V_SS
Coil
C_OSC=100pF
Cap2
Cap1
V_DD
0.1µF Low ESR
Decoupling
Capacitor
EL2
EL1
100Ω
SP4422A
17nF
NOTE:
Keep high voltage traces
short and away from V_DD
and clock lines
SP4422A Test Circuit
SP4422ADS/15
SP4422A Electroluminescent Lamp Driver
5
© Copyright 2000 Sipex Corporation