參數(shù)資料
型號(hào)： SP4439
英文描述： Ultra-Quiet Electroluminescent Lamp Driver with Programmable Wave Shape(超靜場(chǎng)致發(fā)光燈驅(qū)動(dòng)器（可編程波形）)
中文描述： 超靜音電致發(fā)光燈帶可編程波形（超靜場(chǎng)致發(fā)光燈驅(qū)動(dòng)器（可編程波形）驅(qū)動(dòng)程序）
文件頁(yè)數(shù)： 5/13頁(yè)
文件大?。?/td> 193K
代理商： SP4439
5
Rev. 2/15/01 SP4439 Ultra-Quiet Electroluminescent Lamp Driver With Programmable Waveshape Copyright 2000 Sipex Corporation
DESCRIPTION
The SP4439
electroluminescent lamp (EL) driver
is a low-cost low voltage device ideal for the
replacement of LED backlighting designs in cell
phones, PDAs and other portable designs
requiring low acoustic noise.
The SP4439
contains a DC-AC inverter that can produce an
AC output of 160V
P-P
(typical) from +3.0V input
voltage. An internal block diagram of the SP4439
can be found in
Figure 2.
The SP4439
is built on Sipex's dielectrically
isolated BiCMOS process that provides the
isolation required to separate the high voltage
AC signal used to drive the EL lamp from the low
voltage logic and signal processing circuitry.
This ensures latch-up free operation in the
interface between the low voltage CMOS
circuitry and the high voltage bipolar circuitry.
The SP4439
is ideal for applications driving EL
lamps to backlight LCD displays and keypads,
used in cellular radios.
Electroluminescent Technology
An EL lamp is a strip of plastic that is coated with
a phosphorous material which emits light
(fluoresces) when a (>40V) AC signal is applied
across it. Long periods of DC voltages applied
to the lamp tends 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
offers low power single chip driver circuits
specifically designed to drive small to medium
sized electroluminescent panels.
Market Applications
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 consume less power than LEDs
or incandescent bulbs making them ideal for
battery powered products. Also, EL lamps are
able to evenly light an area without creating any
undesirable "hot spots" in the display.
THEORY OF OPERATION
The SP4439
is a DC-AC inverter made up of an
oscillator/frequency divider, a coil/boost
converter, a switched H-bridge network, and a
precision bridge control logic.
The Oscillator/Frequency Divider
The oscillator provides the SP4439 with an on-
chip clock used to control the coil switch (f
COIL
)
and the H-bridge network (f
LAMP
). Although the
oscillator frequency can be varied to optimize
the lamp output, the ratio of f
COIL
/f
LAMP
will
always equal 128.
Figure 2
shows the oscillator output driving the
coil and through 7 flip flops, driving the lamp.
The suggested oscillator frequency is 32kHz for
f
COIL
. The oscillator output is internally divided
down by 7 flip flops to create a second internal
control signal at 250Hz for f
LAMP
.
The Coil/Boost Converter
The supply V
COIL
can range from +2.7V to +9V.
See figure 4 on page 6. V
COIL
should be chosen
such that I
COIL
does not exceed the maximum
coil current specification. The majority of the
current goes through the coil and is typically
much greater than I
DD
.
The inductor is an external component connected
from V
COIL
to the COIL pin of the SP4439.
Energy is stored in the coil according to the
equation
E
L
= 1/2 x L x I
P2
where I
P
, to the first approximation, is the product
I
P
= (t
ON
) x ((V
BATT
- V
CE
)/L)
where t
ON
is the time it takes for the coil to reach
its peak current, V
CE
is the voltage drop across
the internal NPN transistor and L is the inductance
of the coil. When the NPN transistor switch is
off, the energy is forced through an internal
diode which drives the switched H-bridge
network. This energy recovery is directly related
to the brightness of the EL lamp output. There
are many variations among coils; magnetic
material differences, winding differences and
parasitic capacitances.
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