SP4422ADS/15
SP4422A Electroluminescent Lamp Driver
Copyright 2000 Sipex Corporation
1
s
2.2V-5.0V Battery Operation
s
50nA Typical Standby Current
s
High Voltage Output 160 V
PP
typical
s
Internal Oscillator
APPLICATIONS
s
PDAs
s
Cellular Phones
s
Remote Controls
s
Handheld Computers
SP4422A
Electroluminescent Lamp Driver
DESCRIPTION
The SP4422A is a high voltage output DC-AC converter that can operate from a 2.2V-5.0V
power supply. The SP4422A is capable of supplying up to 220 V
PP
signals, making it ideal
for driving electroluminescent lamps. The device features 50 nA (typical) standby current, for
use in low power portable products. One external inductor is required to generate the high
voltage, and one external capacitor is used to select the oscillator frequency. The SP4422A
is offered in an 8-pin narrow and 8-pin micro SOIC packages. For delivery in die form, please
consult the factory.
SP4422A Block Diagram
HON
V
DD
CAP 1
V
SS
COIL
EL2
EL1
SP4422
8
7
4
3
2
1
5
6
CAP 2
SP4422ADS/15
SP4422A Electroluminescent Lamp Driver
Copyright 2000 Sipex Corporation
2
This data sheet specifies environmental parameters, final test conditions and limits as well suggested operating conditions.
For applications which require performance beyond the specified conditions and or limits please consult the factory.
SPECIFICATIONS
(T= 25
C; V
DD
= 3.0V; Lamp Capacitance = 17nF with 100
Series resistor; Coil = 5mH (R
S
= 18
); C
OSC
= 100pF unless otherwise noted)
COIL
V
V
EL 1
EL 2
CAP 1
CAP 2
HON
SP4422A
DD
SS
ABSOLUTE MAXIMUM RATINGS
These are stress ratings only and functional operation of the device at
these ratings or any other above those indicated in the operation sections
of the specifications below is not implied. Exposure to absolute maximum
rating conditions for extended periods of time may affect reliability.
V
DD
............................................................................................................7.0V
Input Voltages/Currents
HON (pin1).........................................-0.5V to (V
DD
+0.5V)
COIL (pin3)..............................................................60mA
Lamp Outputs.............................................................................230V
PP
Storage Temperature.................................................-65C to +150C
PAD
X
Y
EL1
556.5
179.0
EL2
556.2
-151.0
COIL
-19.5
-517.0
HON
-549.0
-256.5
CAP2
-549.0
93.5
CAP1
-568.0
-516.5
NOTES:
1. Dimensions are in Microns unless otherwise noted.
2. Bonding pads are 125x125 typical
3. Outside dimensions are maximum, including scribe area.
4. Die thickness is 10mils +/- 1.
5. Pad center coordinates are relative to die center.
6. Die size 1447 x 1346 ( 57 x 53 mils).
Bonding Diagram:
Power Dissipation Per Package
8-pin NSOIC (derate 6.14mW
o
C above +70
o
C)...................500mW
8-pin
SOIC (derate 4.85mW
o
C above +70
o
C)....................390mW
The information furnished herein by Sipex has been carefully reviewed
for accuracy and reliability. Its application or use, however, is solely the
responsibility of the user. No responsibility for the use of this information
is assumed by Sipex, and this information shall not explicitly or implicitly
become part of the terms and conditions of any subsequent sales
agreement with Sipex. Specifications are subject to change without
prior notice. By the sale or transfer of this information, Sipex assumes
no responsibility for any infringement of patents or other rights of third
parties which may result from its use. No license or other proprietary
rights are granted by implication or otherwise under any patent or
patent rights of Sipex Corporation.
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SP4422ADS/15
SP4422A Electroluminescent Lamp Driver
Copyright 2000 Sipex Corporation
3
THEORY OF OPERATION
The SP4422A is made up of three basic circuit
elements, an oscillator, coil, and switched H-bridge
network. The oscillator provides the device with
an on-chip clock source used to control the charge
and discharge phases for the coil and lamp. An
external capacitor connected between pins 7 and 8
allows the user to vary the oscillator frequency
from 32kHz to 400kHz. The graphs on page 6
show the relationship between C
OSC
and lamp
output voltage. In general, increasing the C
OSC
capacitor will increase the lamp output.
The suggested oscillator frequency is 90kHz
(C
OSC
=100pF). The oscillator output is internally
divided to create two internal control signals, f
COIL
and f
LAMP
. The oscillator output is internally divided
down by 8 flip flops, a 90kHz signal will be
divided into 8 frequencies; 45kHz, 22.5kHz,
11.2kHz, 5.6kHz, 2.8kHz, 1.4kHz, 703Hz, and
352Hz. The third flip flop output (8kHz) is used to
drive the coil (see figure 2 on page 9) and the
eighth flip flop output (250Hz) is used to drive the
lamp. Although the oscillator frequency can be
varied to optimize the lamp output, the ratio of
f
COIL
/f
LAMP
will always equal 32.
The on-chip oscillator of the SP4422A can be
overdriven with an external clock source by
removing the C
OSC
capacitor and connecting a
PIN DESCRIPTION
Pin 1 HON- Enable for driver operation,
high = active; low = inactive.
Pin 2 V
SS
- Power supply common, connect to
ground.
Pin 3 Coil- Coil input, connect coil from V
DD
to pin 3.
Pin 4 Lamp- Lamp driver output2, connect to
EL lamp.
Pin 5 Lamp- Lamp driver output1, connect to
EL lamp.
Pin 6 V
DD
- Power supply for driver, connect to
system V
DD
.
Pin 7 Cap1- Capacitor input 1, connect to C
OSC
.
Pin 8 Cap2- Capacitor input 2, connect to C
OSC
.
1
2
3
4
8
7
6
5
SP4422ACN
Q
Q
HON
SCR1
SCR2
OSC
FF1
FF2
EL Lamp
V
DD
Coil
4
5
EL2
EL1
7
8
Cap1
Cap2
2
V
SS
V
BATTERY
V
DD
6
3
5mH/18
1
C
OSC
= 100pF
0.1
F
f
COIL
f
LAMP
f
LAMP
SP4422A Schematic
SP4422ADS/15
SP4422A Electroluminescent Lamp Driver
Copyright 2000 Sipex Corporation
4
clock source to pin 8. The clock should have a 50%
duty cycle and range fromV
DD
-1V to ground. An
external clock signal may be desirable in order to
synchronize any parasitic switching noise with the
system clock. The maximum external clock
frequency that can be supplied is 400kHz.
The coil is an external component connected from
V
BATTERY
to pin 3 of the SP4422A. Energy is stored
in the coil according to the equation E
L
=1/2LI
2
,
where I is the peak current flowing in the inductor.
The current in the inductor is time dependent and
is set by the "ON" time of the coil switch: I=(V
L
/
L)t
ON
, where V
L
is the voltage across the inductor.
At the moment the switch closes, the current in the
inductor is zero and the entire supply voltage
(minus the V
SAT
of the switch) is across the inductor.
The current in the inductor will then ramp up at a
linear rate. As the current in the inductor builds up,
the voltage across the inductor will decrease due to
the resistance of the coil and the "ON" resistance
of the switch: V
L
=V
BATTERY
-IR
L
-V
SAT
. Since the
voltage across the inductor is decreasing, the current
ramp-rate also decreases which reduces the current
in the coil at the end of t
ON
the energy stored in the
inductor per coil cycle and therefore the light
output. The other important issue is that maximum
current (saturation current) in the coil is set by the
design and manufacturer of the coil. If the
parameters of the application such as V
BATTERY
, L,
RL or ton cause the current in the coil to increase
beyond its rated I
SAT
, excessive heat will be
generated and the power efficiency will decrease
with no additional light output. The Sipex SP4422A
is final tested using a 5mH/18
coil from Hitachi
Metals. For suggested coil sources see page 10.
Typical SP4422A Application Circuit
The supply V
DD
can range from 2.2 to 5.0V. It is not
necessary that V
DD
= V
BATTERY
. V
BATTERY
should not
exceed max coil current specification. The majority
of the current goes through the coil and is typically
much greater than I
DD
.
The f
COIL
signal controls a switch that connects the
end of the coil at pin 3 to ground or to open circuit.
The f
COIL
signal is a 94% duty cycle signal switching
at 1/8 the oscillator frequency. For a 64kHz
oscillator f
COIL
is 8kHz. During the time when the
f
COIL
signal is high, the coil is connected from
V
BATTERY
to ground and a charged magnetic field is
created in the coil. During the low part of f
COIL
, the
ground connection is switched open, the field
collapses and the energy in the inductor is forced
to flow toward the high voltage H-bridge
switches. f
COIL
will send 16 of these charge pulses
(see figure 2 on page 9) to the lamp, each pulse
increases the voltage drop across the lamp in
discrete steps. As the voltage potential approaches
its maximum, the steps become smaller (see figure
1 on page 9).
The H-bridge consists of two SCR structures that
act as high voltage switches. These two switches
control the polarity of how the lamp is charged.
The SCR switches are controlled by the f
LAMP
signal which is the oscillator frequency divided by
256. For a 64kHz oscillator, f
LAMP
=256Hz.
0.1
F Low ESR
Decoupling
Capacitor
EL Lamp
NOTE:
Keep high voltage traces
short and away from V
DD
and clock lines
Cap2
Cap1
V
DD
EL1
HON
V
SS
Coil
EL2
HON=V
DD
=ON
HON=0V=OFF
SP4422A
V
IN
=3V
9mH/35
NOTE:
Keep coil as close to the
SP4422A as possible
+
C
OSC
=100pF
SP4422ADS/15
SP4422A Electroluminescent Lamp Driver
Copyright 2000 Sipex Corporation
5
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 0.1
F 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).
SP4422A Test Circuit
0.1
F Low ESR
Decoupling
Capacitor
NOTE:
Keep high voltage traces
short and away from V
DD
and clock lines
Cap2
Cap1
V
DD
EL1
HON
V
SS
Coil
EL2
HON=V
DD
=ON
HON=0V=OFF
SP4422A
V
IN
=3V
5mH/18
NOTE:
Keep coil as close to the
SP4422A as possible
+
C
OSC
=100pF
100
17nF
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