®
SP4412A
Electroluminescent Lamp Driver
s
2.2 V- 3.6 V Battery Operation
s
50 nA Maximum Standby Current
(10 nA typical)
s
High Voltage Output Typical 160 V
PP
s
External Oscillator Required
s
Enable Control Pin
APPLICATIONS
s
Watches
s
Pagers
s
Backlit LCD Displays
DESCRIPTION
The
SP4412A
is a high voltage output DC-AC converter that can operate from a 2.2V-3.6V
power supply. The
SP4412A
is capable of supplying up to 250 V
PP
signals, making it ideal
for driving small electroluminescent lamps. The device features 10 nA (typical) standby
current, for use in low power portable products. An inductor is used to generate the high
voltage, and an external oscillator is needed as a clock source. The
SP4412A
is offered in
an 8-pin narrow SOIC package or an 8-pin
µSOIC
package. For delivery in die form, please
consult the factory.
HON
No Connect
Osc Input
V
SS
1
2
3
4
SP4412A
8 V
DD
7 EL2
6 EL1
5 COIL
SP4412A Block Diagram
SP4412ADS/12
SP4412ACN 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.
V
DD
..................................................................................................5.0 V
Input Voltages/Currents
HON (pin 1).........................................-0.5V to (V
DD
+0.5V)
COIL (pin 3)..............................................................60mA
Lamp Outputs...............................................................................250V
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
T= 25°C; V
DD
= 3.0V; Lamp Capacitance = 2000pF; Coil = 30 mH at 125 Ohms; External Oscillator = 32768Hz (unless otherwise noted).
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
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
MIN.
2.2
TYP.
3.0
5
MAX.
3.6
2.0
3.6
UNITS
V
mA
V
V
HON
=V
DD
=3V
CONDITIONS
V
DD
-0.25
V
DD
-0.25
1
0
V
DD
10
10
0.25V
V
DD
+0.25
100
50
V
µA
nA
V
HON
=0V
8192
75
60
Hz
%
mA
Input Oscillator=32768Hz
Guaranteed by design.
256
120
160
Hz
V
PP
Input Oscillator=32768Hz
BONDING DIAGRAM
1143
(45)
Measured from center of Pads.
Clk.
HON
Y
V
SS
(0,0)
X
1397
(55)
V
DD
PIN
CLK
HON
V
DD
EL2
EL1
COIL
V
SS
X
218.5
418.5
418.5
-178.0
95.5
-416.0
-416.0
Y
555.5
555.5
339.5
-555.5
-555.5
-555.5
219.0
Coil
Lamp 2
Lamp 1
NOTES:
1. Dimensions are in microns unless otherwise noted (mils)
2. Bonding pads are 125 x 125 microns typical
3. Outside dimensions are maximum including scribe area
4. Die thickness is 15 mils +/- 1
5. Pad center coordinates are relative to the die center.
SP4412ADS/12
SP4412ACN Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
2
PIN DESCRIPTION
THEORY OF OPERATION
1
2
3
4
8
7
6
5
Pin 1 – HON- Enable for driver operation,
high = active; low = inactive.
Pin 2 – NC
Pin 3 – Oscillator clock input
Pin 4 – V
SS
- Power supply common, connect to
ground.
Pin 5 – Coil - Coil input, connect coil from V
DD
to Pin 3.
Pin 6 – Lamp- Lamp driver output1, connect to
EL lamp.
Pin 7 – Lamp- Lamp driver output2, connect to
EL lamp.
Pin 8 – V
DD
- Positive supply.
The
SP4412A
is made up of three basic circuit
elements, a divider chain, a coil, and a switched
H-bridge network. The countdown chain
provides the circuit with a clock source used to
control the charge and discharge phases for the
coil and lamp. An external oscillator is required
and is delivered to pin 3 of the SO-8 package or
to the "Osc in" pad of the bare die. The chart on
page 6 shows the effect of variations in coil
values used. If a clock frequency other than
32kHz is used, the output of the driver as well as
the amount of current used, will be effected.
The suggested oscillator frequency is 32,768Hz.
This clock frequency is internally divided to
create two internal control signals, f
COIL
and
f
LAMP
. The output is internally divided down by
7 flip flops; therefore, a 32,768Hz signal will be
divided into the following frequencies; 32, 16,
8, 4, 2, 1, 0.5 and 0.25kHz. The second flip flop
output (8 kHz) is used to drive the coil (see
figure 2
on
page 7)
and the seventh flip flop
output (256 Hz) 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.
SP4412ACN
V
DD
8
V
DD
Clock
Divider
Chain
V
BATTERY
or V
DD
30 mH at 125Ω
1
HON
5
Coil
External
Clock
f
COIL
3
f
LAMP
Q
FF1
2
NC
FF2
Q
f
LAMP
EL1
6
EL2
7
V
SS
4
EL Lamp
SP4412A Schematic
SP4412ADS/12
SP4412ACN Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
3
The external clock should have a 50% duty
cycle and range from V
DD
-1V to ground. The
maximum external clock frequency is 128 kHz.
The coil is an external component connected
from V
BATTERY
to pin 5 of the
SP4412A.
Energy
is developed in the coil according to the equation
E
L
=1/2LI
2
where the current I is defined as
I=(V
BATTERY
-IR-V
OL
)/R
T
. In order to maximize
the energy produced by the coil, V
BATTERY
should
represent the largest voltage in the system (up to
a maximum of 3.6 v); V
BATTERY
= 3.0 VDC with
a 35mH/125Ω coil is a typical example. It is not
necessary that V
DD
=V
BATTERY
. The coil operation
is a function of the core material and winding
used -- performance variances may be noticeable
from different coil suppliers even though the
values are the same. The
Sipex SP4412A
is
final tested using a 35 mH/135 ohm coil. For
suggested coil sources see
page 8.
The f
COIL
signal controls a switch that connects
the end of the coil at pin 5 to ground or to open
circuit. The f
COIL
signal is a 94% duty cycle
square wave, switching at 1/4 the oscillator
frequency, (for a 32 kHz oscillator f
COIL
is 8
kHz). 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 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 7).
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 128. For a 32kHz 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 6 and 7
which are 180 degrees out of phase with each
other (see
figure 3
on
page 7).
A differential view
of the outputs is shown in
figure 4
on
page 7
.
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 an external inductor and an external
clock signal.
1
3 VDC
2
3
4
HON
V
DD
Lamp
8
7
6
5
Coil
LAMP
30 mH 125 ohm Coil
Clk
V
SS
Lamp
Coil
32-64 Khz
Typical SP4412ACN Application Circuit
SP4412ADS/12
SP4412ACN Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
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
current 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, 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).
SP4412ADS/12
SP4412ACN Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
5
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