ZSP4422A Electroluminescent Lamp Driver
Zywyn
Features
•
•
•
•
+2.2V to +5.0V battery operation
50nA typical standby current
High voltage output typical 160V
PP
Internal oscillator
ZSP4422A
Electroluminescent Lamp Driver
General Description
The ZSP4422A is a high voltage output DC-AC converter
that can operate from a +2.2V to +5.0V power supply. The
ZSP4422A is designed with our proprietary high voltage
BiCMOS technology and is capable of supplying up to
160V
PP
signals, making it ideal for driving small electrolu-
minescent lamps. The device features 50nA (typical)
standby current, for use in low power portable products.
One external inductor is required to generate the high
voltage, and an external capacitor is used to select the
oscillator frequency. The ZSP4422A is offered in an 8-pin
narrow SOIC package or an 8-pin MSOP package. For
delivery in die form, please consult the factory.
Applications
•
•
•
•
PDAs
Cellular phones
Remote controls
Handheld computers
Pin Configuration
Ordering Information
Part Number
ZSP4422ACN
ZSP4422ACU
ZSP4422ACX
Temperature Range
–40°C to +85°C
–40°C to +85°C
0°C to +70°C
n/a
n/a
Package Type
8-Pin nSOIC
8-Pin MSOP
Die in Wafflepack
nSOIC Eval. Board
MSOP Eval. Board
HON 1
V
SS
2
COIL 3
EL2 4
8
CAP2
CAP1
V
DD
EL1
ZSP4422ANEB
ZSP4422AUEB
Zywyn
ZSP4422A
7
6
5
Please contact the factory for pricing and availabiliy on a Tape-on-Reel
option.
8-Pin nSOIC/MSOP
Please contact the factory for EL driver design support and availability of
custom-made evaluation demo boards.
Zywyn Corporation • Tel (408) 733-3225 • Fax (408) 733-3206 • Email sales@zywyn.com • www.zywyn.com
specifications subject to change without notice
March 2004
rev. 01
Zywyn Corporation
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 is
not implied. Exposure to absolute maximum rating condi-
tions for extended periods of time may affect reliability.
V
DD .................................................................................................
+7.0V
Input Voltages/Currents
HON (pin 1) ................................... –0.5V to (V
DD
+0.5V)
COIL (pin3)..............................................................60mA
Lamp Output .......................................................... 230V
PP
Storage Temperature .............................. –65°C to +150°C
Operating Temperature ............................. –40°C to +85°C
Power Dissipation Per Package
8-pin NSOIC (derate 6.14mW/°C above +70°C) ... 500mW
8-pin µSOIC (derate 4.85mW/°C above +70°C) ... 390mW
ZSP4422A
Storage Considerations
Storage in a low humidity environment is preferred. Large
high density plastic packages are moisture sensitive and
should be stored in Dry Vapor Barrier Bags. Prior to usage,
the parts should remain bagged and stored below 40°C
and 60%RH. If the parts are removed from the bag, they
should be used within 48 hours or stored in an environ-
ment at or below 20%RH. If the above conditions cannot
be followed, the parts should be baked for four hours at
125°C in order remove moisture prior to soldering. Zywyn
ships product in Dry Vapor Barrier Bags with a humidity
indicator card and desiccant pack. The humidity indicator
should be below 30%RH.
The information furnished by Zywyn has been carefully
reviewed for accuracy and reliability. Its application or
use, however,is solely the responsibility of the user. No
responsibility of the use of this information become part of
the terms and conditions of any subsequent sales agree-
ment with Zywyn. Specifications are subject to change
without the responsibility for any infringement of patents
or other rights of third parties which may result from its
use. No license or proprietary rights are granted by impli-
cation or otherwise under any patent or patent rights of
Zywyn Corporation.
Electrical Characteristics
T
A
= +25°C, V
DD
= +3.0V, C
LAMP
= 17nF with 100Ω series resistor, Coil = 5mH (R
S
= 18Ω); C
OSC
= 100pF, unless otherwise noted.
Symbol
V
DD
I
COIL
+ I
DD
V
COIL
V
HON
Parameter
Supply Voltage
Supply Current
Coil Voltage
HON Input Voltage
LOW: EL off
HIGH: EL on
HON Current
Shutdown Current
V
DD
- V
HON
- +3.0V
V
DD
= +3.0V, V
HON
= LOW
V
DD
= +5.0V, V
HON
= LOW
INDUCTOR DRIVE
f
COIL
= f
LAMP
x 32
I
PK-COIL
EL LAMP OUTPUT
f
LAMP
V
PP
EL Lamp Frequency
Peak-to-Peak Output Voltage
T
A
= +25°C, V
DD
= +3.0V
T
A
= +25°C, V
DD
= +2.2V
T
A
= +25°C, V
DD
= +3.0V
T
A
= +25°C, V
DD
= +5.0V
250
200
60
110
180
350
80
140
200
V
500
600
Hz
Coil Frequency
Coil Duty Cycle
Peak Coil Current
Guaranteed by design
11.2
94
60
kHz
%
mA
V
DD
= +3.0V, V
HON
= +3.0V
V
DD
= +5.0V, V
HON
= +5.0V
V
DD
–0.25
V
DD
– 0.25
0
V
DD
25
50
0.3
Condition
Min
2.2
Typ
3.0
20
40
Max
5.0
30
60
5.0
0.25
V
DD
+ 0.25
60
500
Units
V
mA
V
V
µA
nA
µA
I
HON
I
SD
= I
COIL
+ I
DD
Zywyn
2
March 2004
rev. 01
Zywyn Corporation
Circuit Description
The ZSP4422A 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. 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 1)
and the eighth flip-flop output (250Hz)
is used to drive the lamp. Although the oscillator fre-
quency 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 ZSP4422A can be overdriven
with an external clock source by removing the C
OSC
capacitor and connecting a clock source to pin 8. The
clock should have a 50% duty cycle and range from
V
DD
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 ZSP4422A. 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 Zywyn ZSP4422A is final
tested using a 5mH/18Ω coil from Hitachi Metals. For
suggested coil sources see,
“Coil Manfacturers.”
ZSP4422A
The supply V
DD
can range from +2.2V 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 mag-
netic field is created in the coil. During the low part of f
COIL
,
the ground connection is switched open, the field col-
lapses 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 5)
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 4).
The H-bridge consists of two proprietary low on-resis-
tance high-voltage switches. These two switches control
the polarity of how the lamp is charged. The high-voltage
switches are controlled by the f
LAMP
signal which is the
oscillator frequency divided by 256. For a 64kHz oscillator,
f
LAMP
= 256Hz. The direction of current flow is determined
by which high-voltage switch 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 6).
A differential repre-
sentation of the outputs is shown in
Figure 7.
Layout Considerations
The ZSP4422A circuit board layout must observe careful
analog precautions. For applications with noisy voltage
power supplies a 0.1µF 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 trans-
former, transistors, and several resistors and capacitors.
Zywyn
4
March 2004
rev. 01
Zywyn Corporation
This approach is large and bulky, and cannot be imple-
mented in most hand held equipment. Zywyn 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
ZSP4422A
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.
Typical Application
Figure 2. Typical Application Circuit
Contact the factory for any technical and application support.
Test Circuit
5mH/18Ω
HON=V
DD
=ON
HON=0V=OFF
V
IN
=3V
C
OSC
=100pF
HON
V
SS
Coil
EL2
Cap2
Cap1
V
DD
EL1
ZSP4422A
100Ω
17nF
0.1µF Low ESR
Decoupling
Capacitor
+
-
NOTE:
Keep coil as close to the
ZSP4422A as possible
NOTE:
Keep high voltage traces
short and away from V
DD
and
clock lines
Zywyn
Figure 3. Typical Test Circuit
5
March 2004
rev. 01
Embedded System
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