®
SP4423
Electroluminescent Lamp Driver
Low Power Applications
s
2.2V-5.0V Battery Operation
s
50nA Maximum Standby Current
s
High Voltage Output 160 V
PP
typical
s
Internal Oscillator
APPLICATIONS
s
PDAs
s
Cellular Phones
s
Remote Controls
s
Hand Held Computers
DESCRIPTION
The
SP4423
is a high voltage output DC-AC converter that can operate from a 2.2V-6.0V
power supply. The
SP4423
is capable of supplying up to 200 V
PP
signals, making it ideal for
driving electroluminescent lamps. The device features 10nA (typical) standby current, for use
in low power portable products. An inductor is used to generate the high voltage, and an
external capacitor is used to select the oscillator frequency. The
SP4423
is offered in
an 8-pin narrow SOIC and 8-pin
µSOIC
packages. For delivery in die form, please consult
the factory.
HON
V
SS
COIL
EL2
1
2
3
4
SP4423
8
7
6
5
CAP 2
CAP 1
V
DD
EL1
Block Diagram
SP4423DS/14
SP4423Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
1
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....................................................-65˚C to +150˚C
Power Dissipation Per Package
8-pin NSOIC (derate 6.14mW
o
C above +70
o
C)..................500mW
8-pin
µSOIC
(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.
SPECIFICATIONS
PARAMETER
Supply Voltage, V
DD
Supply Current, I
COIL
+I
DD
Coil Voltage, V
COIL
HON Input Voltage, V
HON
LOW: EL off
HIGH: EL on
HON Current, EL on
V
DD
-0.25
V
DD
-0.25
0
V
DD
25
50
10
0.3
MIN.
2.2
TYP.
3.0
5
12
(T= 25°C; V
DD
= 3.0V; Lamp Capacitance = 6000pF; Coil = 20 mH (R
S
= 70Ω); C
OSC
= 150pF unless otherwise noted)
MAX.
6.0
12
40
6.0
UNITS
V
mA
V
CONDITIONS
V
DD
=3.0V, V
HON
=3.0V
V
DD
=6.0V, V
HON
=6.0V
0.25V
V
DD
+0.25
60
120
200
1
V
µA
nA
µA
V
HON
=V
DD
=3.0V
V
HON
=V
DD
=6.0V
V
DD
=3.0V, V
HON
=0V
V
DD
=6.0V, V
HON
=0V
Shutdown Current, I
SD
=I
COIL
+I
DD
INDUCTOR DRIVE
Coil Frequency, f
COIL
=f
LAMP
x32
Coil Duty Cycle
Peak Coil Current, I
PK-COIL
EL LAMP OUTPUT
EL Lamp Frequency, f
LAMP
Peak to Peak Output Voltage
200
225
110
9.6
75
60
kHz
%
mA
Guaranteed by design.
300
300
150
400
450
Hz
V
PP
V
DD
=3.0V
V
DD
=6.0V
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.
Bonding Diagram:
V
DD
CAP 1
PAD
EL1
EL2
COIL
V
SS
HON
CAP2
CAP1
V
DD
X
556.5
556.2
-19.5
-568.0
-549.0
-549.0
-568.0
-349.0
Y
179.0
-151.0
-517.0
-517.0
-256.5
93.5
-516.5
517.0
EL 1
CAP 2
EL 2
HON
SP4423
537A
V
SS
SP4423DS/14
COIL
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 10 mils +/- 1.
5. Pad center coordinates are relative to die center.
6. Die size 1447 x 1346 ( 57 x 53 mils).
SP4423 Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
2
PIN DESCRIPTION
THEORY OF OPERATION
The
SP4423
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 voltage and decrease
the lamp frequency.
The suggested oscillator frequency is 64kHz
(C
OSC
=150pF). 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 64kHz signal
will be divided into 8 frequencies; 32, 16, 8, 4,
2, 1, 0.5, and 0.25 Hz. The 3rd flip flop output
(8kHz) is used to drive the coil (see
Figure 2
on
page 9)
and the 8th 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.
1
2
3
4
8
7
6
5
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
.
SP4423
0.1µF
V
DD
6
V
DD
C
OSC
= 150pF
V
BATTERY
20mH/70Ω
1
HON
3
Coil
7
OSC
Cap1
Cap2
f
COIL
SCR1
SCR2
8
Q
f
LAMP
FF1
FF2
Q
f
LAMP
EL2
4
EL1
5
V
SS
2
EL Lamp
SP4423 Schematic
SP4423DS/14
SP4423Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
3
The on-chip oscillator of the
SP4423
can be
overdriven with an external clock source by
removing the C
OSC
capacitor and connecting a
clock source to pin 8 (Cap 2). 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 frequencies that can
be supplied is 400kHz.
The coil is an external component connected from
V
BATTERY
to pin 3 of the
SP4423.
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 t
ON
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 SP4423
is final tested using a 20mH/70Ω
coil from CTC. For suggested coil sources see
page 10.
The supply V
DD
can range from 2.2 to 6.0V. It is not
necessary that Vdd = 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 75% 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
SP4423DS/14
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 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
shorter (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
=250Hz.
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 with each
other (see
Figure 3
on
page 9).
A differential
representation of the outputs is shown in
Figure
4
on
page 9.
To minimize AC interference it is
advisable to use a decoupling filter capacitor
between V
DD
and ground.
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.
© Copyright 2000 Sipex Corporation
SP4423 Electroluminescent Lamp Driver
4
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 incandescent 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. 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).
9mH/35Ω
HON=V
DD
=ON
HON=0V=OFF
V
IN
=3V
C
OSC
=100pF
HON
V
SS
Coil
EL2
Cap2
Cap1
V
DD
EL1
SP4423
EL Lamp
0.1µF Low ESR
Decoupling
Capacitor
+
–
NOTE:
Keep coil as close to the
SP4423 as possible
NOTE:
Keep high voltage traces
short and away from V
DD
and clock lines
Typical SP4423 Application Circuit
20mH/70Ω
HON=V
DD
=ON
HON=0V=OFF
V
IN
=3V
C
OSC
=150pF
HON
V
SS
Coil
EL2
Cap2
Cap1
V
DD
EL1
SP4423
100Ω
6nF
0.1µF Low ESR
Decoupling
Capacitor
+
–
NOTE:
Keep coil as close to the
SP4422A as possible
NOTE:
Keep high voltage traces
short and away from V
DD
and clock lines
Typical SP4423 Test Circuit
SP4423DS/14
SP4423Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
5
