®
SP4405
Low Voltage Electroluminescent Lamp Driver
with Regulated Output Voltage
s
+2.2V to +4.5V Battery Operation
s
DC-to-AC Converter Produces
160V
PP
typical for EL Display Panels
s
Single Resistor Controlled Internal
Oscillator
s
Low Current Standby Mode
s
Internal Feedback Loop Maintains
a Constant Regulated EL Lamp
Voltage Output
APPLICATIONS
s
Pagers
s
Cellular Phones
s
PDAs
DESCRIPTION
The
SP4405
is a high voltage output DC-AC inverter specifically designed to drive
electroluminescent lamps to backlight liquid crystal displays, keypads, and backlit readouts
used in battery operated portable equipment. The
SP4405
will operate from a +2.2V to +4.5V
battery source. The device features an internal feedback loop that regulates the lamp voltage
output to 160V
PP
(typical) with varying supply voltages to maintain constant EL lamp brightness
over the life of the battery. The device also has a low power shutdown mode which draws less
than 50nA (typical), ideal for low power portable products. One external inductor is required
to generate the high voltage AC output. One external resistor is used to set the internal
oscillator frequency. The
SP4405
is ideal for portable applications such as pagers, cellular
phones, PDAs, and other portable applications using LCDs in dim or low light environments.
The
SP4405
is offered in 8-pin SOIC and 8-pin
µSOIC
packages.
V
BATTERY
ELEN 1
V
SS
2
COIL 3
EL1 4
SP4405
8 R
OSC
7 C
INT
6
5
V
DD
EL2
C1
0.1µF
ELEN
1
L1
470µH
SP4405
V
DD
R
OSC
450kΩ
6
3
COIL
*D1
1N4148
R
OSC
8
7
C
INT
C2
1nF
2
V
SS
4
EL1
5
EL2
C
INT
0.1µF
EL Lamp
*optional device
SP4405DS/18
SP4405 Low Voltage Electroluminescent 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.
Power Supply, V
BATTERY
.....................................................................7.0V
Input Voltages, ELEN (pin 1)....................................-0.5V to (V
DD
+0.5V)
Lamp Outputs...............................................................................200V
PP
Operating Temperature...................................................-40˚C to +85˚C
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
V
BATTERY
= 3.0V, L = 470µH/3.9Ω, R
OSC
= 450KΩ, C
LAMP
= 6.8nF, T
AMB
= 25
O
C and C
INT
= 0.1µF unless otherwise noted; refer to test circuit.
PARAMETER
Supply Voltage, V
DD
Supply Current, I
COIL
+I
DD
Coil Voltage, V
COIL
ELEN Input Voltage, V
ELEN
LOW: EL off
HIGH: EL on
Shutdown Current, I
SD
=I
COIL
+I
DD
INDUCTOR DRIVE
Coil Frequency, f
COIL
=f
LAMP
x128
Coil Duty Cycle
Peak Coil Current, I
PK-COIL
EL LAMP OUTPUT
EL Lamp Frequency, f
LAMP
Peak to Peak Output Voltage
MIN.
2.2
TYP.
3.0
39
27
MAX.
4.5
55
70
4.5
UNITS
V
mA
V
V
DD
=3.0V
V
DD
=4.5V
CONDITIONS
V
DD
-0.25
V
DD
-0.25
0
V
DD
0.1
0.25V
V
DD
+0.25
1.0
V
µA
V
DD
=4.5V
48.6
90
60
kHz
%
mA
Guaranteed by design.
320
120
150
380
160
500
190
200
Hz
V
PP
V
DD
=3.0V
V
DD
=4.5V
SP4405DS/18
SP4405 Low Voltage Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
2
TEST CIRCUIT
V
BATTERY
Pin 3 — COIL — Coil. The inductor for the
EL lamp is connected from V
BATTERY
to this
input pin.
Pin 4 — EL1 — Eluminescent Lamp. This is
a lamp driver output pin to connect to the
EL lamp.
Pin 5 — EL2 — Eluminescent Lamp. This is
a lamp driver output pin to connect to the
EL lamp.
Pin 6 — V
DD
— Positive Battery Power Supply.
Connect such that +2.2V < V
DD
< +4.5V.
50Ω
6.8nF
ELEN
1
L1
470µH
SP4405
V
DD
R
OSC
750kΩ
6
3
COIL
D1
1N4148
R
OSC
8
7
C
INT
C1
0.1µF
C2
1nF
2
V
SS
C
INT
0.1µF
4
EL1
5
EL2
EL Lamp
50Ω
1MΩ
PIN ASSIGNMENTS
Pin 1 — ELEN — Eluminescent Lamp Enable.
When driven HIGH, this input pin enables
the EL driver output EL1 and EL2 (pins 4 and
5, respectively) to the EL lamp.
Pin 2 — V
SS
— Power Supply Common.
Connect to the lowest circuit potential,
typically ground.
Pin 7 — C
INT
— Integrating Capacitor.
Connecting a fast recovery diode from
COIL (pin 3) to this input pin increases
the light output of the EL lamp. An
integrating capacitor (0.1µF) connected
from this pin to ground filters out any coil
switching spikes or ripple present in the
output waveform to the EL lamp.
Pin 8 — R
OSC
— Oscillator Resistor. Connecting
a 450kΩ resistor to this input pin sets the
frequency of the internal clock.
PINOUT
ELEN 1
V
SS
2
COIL 3
EL1 4
SP4405
8 R
OSC
7 C
INT
6
5
V
DD
EL2
SP4405DS/18
SP4405 Low Voltage Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
3
DESCRIPTION
The
SP4405
Electroluminescent Lamp Driver
is a low-cost low voltage device ideal for the
replacement of LED backlighting designs in
keypads, handsets, PDAs and other portable
designs. The
SP4405
contains a DC-AC inverter
that can produce an AC output of 160V
PP
(typical)
from a +2.2V to +4.5V input voltage. An
internal feedback loop regulates the lamp voltage
output to 160V
PP
(typical) with varying supply
voltages to maintain constant EL lamp
brightness. An internal block diagram of the
SP4405
can be found in
Figure 1.
The
SP4405
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.
A total of only six external components are
required for the standard operation of the
SP4405:
an inductor, a fast recovery diode,
three capacitors and a resistor. A diagram of the
SP4405
in a typical application can be found in
Figure 2.
Electroluminescent Technology
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
V
BATTERY
SP4405
3 COIL
V
REF
=1.25V
L2
470µH, 3Ω
7 C
INT
ERROR
COMPARATOR
V
DD
R
OSC
450kΩ
6
SCR1
f
COIL
R
OSC
8
OSC
SCR2
D1
1N4148
*
C
INT
0.1µF
**
C
1
0.1µF
C
2
1nF
Q
FF7
Q
f
LAMP
f
LAMP
2
V
SS
1
ELEN
4
EL1
5
EL2
EL Lamp
NOTES: *
Optional Component
**
C
INT
may be decreased to change the square wave output to a sawtooth waveform.
Figure 1. Internal Diagram of the SP4405
SP4405DS/18
SP4405 Low Voltage Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
4
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 can be
difficult to implement in some smaller hand
held equipment.
Sipex
now 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 typically 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
SP4405
is a DC-AC inverter made up of:
1. The Oscillator/Frequency Divider, 2. The
Coil, and 3. The Switched H-bridge Network.
Further details of each element follow.
The Oscillator/Frequency Divider
The oscillator provides the
SP4405
with an
on-chip clock used to control the coil switch
(f
COIL
) and the H-bridge network (f
LAMP
and 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 1
shows the oscillator output driving the
coil and the output of the oscillator with 7 flip
flops driving the lamp. The suggested oscillator
frequency is 48.6kHz (R
OSC
= 450kΩ) for f
COIL
.
The oscillator output is internally divided down
by 7 flip flops to create a second internal control
signal at 380Hz for f
LAMP
.
V
BATTERY
ELEN
1
L1
470µH
SP4405
V
DD
R
OSC
450kΩ
6
3
COIL
*D1
1N4148
R
OSC
8
7
C
INT
C1
0.1µF
C2
1nF
2
V
SS
4
EL1
5
EL2
C
INT
0.1µF
EL Lamp
*optional device
Figure 2. Typical Application Circuit for the SP4405, Set
for a Square Wave Output with C
INT
= 0.1µF
The Coil
The supply V
BATTERY
can range from +2.2V to
+4.5V. V
BATTERY
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 coil is an external component connected
from V
BATTERY
to pin 3 of the
SP4405.
Energy is
stored in the coil according to the equation
E
L
=1/2LI
P2
where I
P
, to the first approximation,
is the product I
P
= (t
ON
) (V
BATTERY
- 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 for f
COIL
, 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.
For suggested coil suppliers, refer to
Page 7.
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 90% duty cycle
signal switching at the oscillator frequency,
SP4405DS/18
SP4405 Low Voltage Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
5
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