ZSP4491 Two Panel Electroluminescent Lamp Driver
Zywyn
General Description
Features
• Single IC drives 2 EL lamps for backlighting:
• Cell phone keypad and LCD
• Multi-color EL lamps
• Multi-segment EL lamps
• Control over lamp-A and lamp-B for indepen-
dent or concurrent operation
• +2.2V to +5.0V battery operation
• Single coil used to generate high voltage AC
outputs
• Low power standby mode draws 100nA typical
current
• A single resistor controls the internal oscillator
• DC-AC inverter produces up to 220V
PP
• Space-saving 10-pin MSOP package
ZSP4491
Two Panel Electroluminescent Lamp Driver
Applications
•
•
•
•
•
•
Cellular phones
PDA’s
EL keypads & dashboards
Handheld GPS units
Security systems
POS terminals
The ZSP4491 electroluminescent lamp driver provides
designers of cell phones PDA’s and other handheld, por-
table electronic devices with an integrated solution for
driving two EL lamps independently or concurrently. The
ZSP4491 is designed with our proprietary high voltage
BiCMOS technology. The ZSP4491 reduces system cost,
component count and board space requirements over a
discrete 2-EL driver approach. The EL lamps operate in
opposite phase so the ZSP4491 can be easily imple-
mented in applications driving multi-color or multi-seg-
ment EL lamps. The ZSP4491 operates from a +2.2V to
+5.0V battery source. The device features a low power
standby mode which draws less than 1mA. The frequency
of the internal oscillator is set using a single external
resistor. A single external inductor is required to generate
the high voltage AC outputs to drive the EL lamps. All
input pins are ESD protected with internal diodes to V
DD
and V
SS
.
Ordering Information
Part Number
ZSP4491CW
ZSP4491CX
ZSP4491EU
ZSP4491LEU
ZSP4491UEB
Temperature Range
0°C to +70°C
0°C to +70°C
–40°C to +85°C
–40°C to +85°C
n/a
Package Type
Die in Wafer Form
Die in Wafflepack Form
10-Pin MSOP
10-Pin MSOP Green
Evaluation Board
Pin Configuration
Please contact the factory for pricing and availabiliy on a Tape-on-Reel
and Green Package
option.
ELEN1
V
DD
R
OSC
ELEN2
V
SS
1
2
3
4
5
10
EL1
EL2
ELcommon
CAP
COIL
Please contact the factory for EL driver design support and availability
of custom-made evaluation demo boards.
See our web site for Application Note
AN007
regarding requirements
for custom-made evaluation demo boards.
Zywyn
ZSP4491
9
8
7
6
10-Pin MSOP
Zywyn Corporation • Tel (408) 733-3225 • Fax (408) 733-3206 • Email sales@zywyn.com • www.zywyn.com
specifications subject to change without notice
July 2005
rev. 03
Zywyn Corporation
ZSP4491
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.
Supply Voltage, V
DD ................................................................
+7.0V
Input Voltages, Logic ......................... –3.0V to (V
DD
+0.3V)
Lamp Outputs ......................................................... 220V
PP
Storage Temperature .............................. –65°C to +150°C
Operating Temperature ............................. –40°C to +85°C
Power Dissipation Per Package
10-pin MSOP (derate 8.84mW/°C above +70°C) . 720mW
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, L
COIL
= 2.2mH, R
OSC
= 560kΩ, EL Lamp Load = 4.7nF; C
INT
= 1000pF, unless otherwise noted.
Symbol
V
DD
I
DD
V
COIL
V
ELEN1
, V
ELEN2
Parameter
Supply Voltage
Supply Current
Coil Voltage
ELEN1/ELEN2 LOW Threshold
ELEN1/ELEN2 HIGH Threshold
Shutdown Current
V
DD
= +2.8V to +5.0V
V
DD
= +2.2V to +2.8V
V
ELEN
= 0V
T
A
= +25°C
V
DD
- 0.25
V
DD
x 0.61
1.7
0
V
DD
V
DD
0.1
Condition
Min
2.2
Typ
3.0
10
Max
5.0
55
5.0
+0.25
V
DD
+ 0.25
V
DD
+ 0.25
1
Units
V
mA
V
V
V
V
µA
I
SD
= I
COIL
+ I
DD
INDUCTOR DRIVE
f
COIL
I
COIL
I
PK-COIL
EL LAMP OUTPUT
f
LAMP
V
PP
Coil Frequency
Coil Duty Cycle
Coil Current
Peak Coil Current
44.0
90
9
45
90
kHz
%
mA
mA
Guaranteed by design
20
EL Lamp Frequency
Peak-to-Peak Output Voltage
T
A
= +25°C, V
DD
= +3.0V
T
A
= +25°C, V
DD
= +3.0V
250
140
350
180
Hz
V
Zywyn
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July 2005
rev. 03
Zywyn Corporation
ZSP4491
Block Diagram
6 COIL
V
BATT
L1
2.2mH
V
BATT
V
DD
2
Zywyn
ZSP4491
HV
1
560kΩ
R
OSC
3
C2*
1nF
OSC
f
COIL
D1
1N4148
9 CAP
C
INT
1000pF
HV
2
HV
3
HV
4
C1
0.1µF
f
LAMP1
* optional device
FF7
f
LAMPCOM
ELEN1
ELEN2
1
4
0
1
f
LAMP2
5
V
SS
EL1
10
8
ELcommon
9
EL2
EL Lamp
EL Lamp
Figure 1. Internal Block Diagram
Pin Description
Pin Number
1
2
3
4
5
6
7
Pin Name
ELEN1
V
DD
R
OSC
ELEN2
V
SS
COIL
CAP
Pin Function
Electroluminescent Lamp Enable Control Line 1. This is a control line to
enable a single or dual EL lamp output. Refer to
Table 1
for the control logic.
Positive Battery Power Supply.
Oscillator Resistor. Connecting a resistor between this input pin and V
DD
sets
the frequency of the internal clock.
Electroluminescent Lamp Enable Control Line 2. This is a control line to enable
a single or dual EL lamp output. Refer to
Table 1
for the control logic.
Power Supply Common. Connect to the lowest circuit potential, typically
ground.
Coil. The inductor for the boost converter is connected from V
BATT
to this input
pin.
Integrator Capacitor. An integrating capacitor connected from this pin to
ground filters out any coil switching spikes or ripple present in the output
waveform to the EL lamps. Connecting a fast recovery diode from COIL to
CAP increases the light output of the EL lamp.
Electroluminescent Common. This is a high voltage lamp driver output pin
common to both EL lamps.
Electroluminescent Lamp Output 2. This is a high voltage lamp driver output pin
connect to the second EL lamp.
Electroluminescent Lamp Output 1. This is a high voltage lamp driver output pin
to connect to the first EL lamp.
8
9
10
EL COMMON
EL2
EL1
ELEN1
0
0
1
1
ELEN2
0
1
0
1
EL1 Output
OFF
OFF
ON
ON
EL2 Output
OFF
ON
OFF
ON
Table 1. Control Line Logic Table
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Zywyn Corporation
ZSP4491
E
L
= 1/2 (LI
pk2
) where I
pk
= (t
ON
) • (V
BATT
– V
CEsat
)/L
An internal oscillator controls the coil switch. During the
time the coil switch is on, the coil is connected between
V
DD
and the saturation voltage of the coil switch.
While the coil is connected between V
DD
and coil switch
and a magnetic field develops in the coil. When the coil
switch turns off, the switch opens, the magnetic field
collapses and the voltage across the coil rises. The inter-
nal diode forward biases when the coil voltage rises above
the H-Bridge voltage and the energy enters the EL lamp.
Each pulse increases the voltage across the lamp in
discrete steps.
As the voltage approaches its maximum, the steps be-
come smaller. See
Figure 4.
The brightness of the EL lamp output is directly related to
energy recovery in the boost converter. There are many
variations among coils such as magnetic core differences,
winding differences and parasitic capacitances. For sug-
gested coil suppliers, see
“Coil Manufacturers.”
Circuit Description
The ZSP4491 electroluminescent lamp driver provides
designers of cell phones, PDA’s and other handheld,
portable electronic devices with an integrated solution for
driving two EL lamps independently or simultaneously.
The ZSP4491 reduces system cost, component count and
board space requirements over a discrete 2 EL driver
approach. The EL lamps operate in opposite phase so the
ZSP4491 can be easily implemented in applications driv-
ing multi-color or multi-segment EL lamps. The ZSP4491
operates from a +2.2V to +5.0V battery source. The
device features a low power standby mode that draws less
than 1µA. The frequency of the internal oscillator is set
using a single external resistor. A single external inductor
is required to generate the high voltage AC outputs to
drive the EL lamps. All input pins are ESD protected with
internal diodes to V
DD
and V
SS
.
The ZSP4491 contains a DC-AC inverter that can produce
an AC output of 180V
PP
(typical) from a +3.0V input
voltage. An internal block diagram of the ZSP4491 can be
found in
Figure 1.
Electroluminescent Technology
An EL lamp consists of a thin layer of phosphorous
material sandwiched between two strips of plastic which
emits light (flouresces) when a high voltage AC signal is
applied across it. It behaves primarily as a capacitive load.
Long periods of DC voltage applied to the material tend to
reduce its lifetime. With these conditions in mind, the ideal
signal to drive an EL lamp is a high voltage sine wave.
Traditional approaches to achieve this type of waveform
include discrete circuits incorporating a transformer, tran-
sistors and several resistors and capacitors.
This approach is large and bulky and cannot be imple-
mented in most handheld equipment. Zywyn offers low
power single chip driver circuits specifically designed to
drive small to medium sized electroluminescent panels.
Zywyn EL drivers provide a differential AC voltage without
a DC offset to maximize EL lamp lifetime. The only addi-
tional components required for the EL driver circuitry are
an inductor, resistor and capacitor.
Electroluminescent backlighting is ideal when used with
LCD displays, keypads or other back-lit readouts. EL
lamps uniformly light an area without creating any undesir-
able “hot spots” in the display. Also, an EL lamp typically
consumes less power that LED’s or incandescent bulbs in
similar lighting situations. These features make EL ideal
for attractive, battery powered products.
Oscillator
The internal oscillator generates a high frequency clock
used by the boost converter and H-Bridge. An external
resistor from V
DD
to R
OSC
sets the oscillator frequency.
Typically a 560kΩ resistor sets the frequency to 44.0kHz.
The high frequency clock directly controls the coil switch.
This high frequency clock is divided by 128 to generate a
low frequency clock which controls the EL H-Bridge and
sets the EL lamp frequency. The oscillator has low sensi-
tivity to temperature and supply voltage variations, in-
creasing the performance of the EL driver over the oper-
ating parameters.
Dual H-Bridge
The H-Bridge consists of two proprietary low on-resis-
tance high voltage switches, and two NPN transistors that
control how the lamp is charged. There are four operating
states that can be applied to the ZSP4491. See
Table 1.
Setting ELEN1 to HIGH always activates the H-Bridge and
illuminates the lamp connected between EL1 and
Elcommon. Setting ELEN2 to HIGH always activates the
H-Bridge and illuminates the lamp connected between
EL2 and Elcommon. If both ELEN1 and ELEN2 are set to
HIGH then both lamps are illuminated. Setting both ELEN1
and ELEN2 to LOW disables the outputs and places the
circuit in a low power state. The EL driver illuminates the
lamp by applying the high voltage supply of the boost
converter to the lamp terminals through the H-Bridge and
then switching the terminal polarity between the high
voltage supply and ground at a constant frequency. This
applies an AC voltage to the lamp that is twice the peak
output voltage of the boost driver. An AC voltage greater
than the 40V across the terminals of the lamp is typically
necessary to adequately illuminate the EL lamp.
Theory Of Operation
Coil Switch
The ZSP4491 has an inductor-based boost converter to
generate the high voltage used to drive the EL lamp.
Energy is stored in the inductor according to the equation:
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ZSP4491
Design Considerations
Inductor Selection
If limiting peak current draw from the power supply is
important, small coil values (<1mH) may need a higher
oscillator frequency. Inductor current ramps faster in a
lower inductance coil than a higher inductance coil for a
given coil switch on time period, resulting in higher peak
coil currents.
It is important to observe the saturation current rating of a
coil. When this current is exceeded, the coil is incapable
of storing any more energy and then ceases to act as an
inductor. Instead, the coil behaves according to its series
DC resistance.
Since small coils (<1mH) have inherently low series DC
resistance, the current can peak dramatically through a
small coil during saturation. This situation results in wasted
energy not stored in the magnetics of the coil but ex-
pressed as heating which could lead to failure of the coil.
Generally, selecting a coil with lower series DC resistance
will result in a system with higher efficiency and lamp
brightness.
Increasing Light Output
EL lamp light output can be improved by connecting a fast
recovery diode from the COIL pin to the CAP pin. The
internal diode is bypassed resulting in an increase in light
output at the EL lamp. We suggest a fast recovery diode
such as the industry standard 1N4148.
The optimal value of C
INT
will vary depending on the lamp
parameters and coil value. Lower C
INT
values can decrease
average supply current but higher C
INT
values can increase
lamp brightness. This is best determined by experimenta-
tion. A rule of thumb is larger coils (1mH) are paired with
a smaller C
INT
(680pF) and smaller coils (470µH) are paired
with a larger C
INT
(1800pF).
Changing the EL lamp Output Voltage Waveform
Designers can alter the sawtooth output voltage waveform
to the EL lamp. Increasing the capacitance of the integra-
tion capacitor, C
INT
, will integrate the sawtooth waveform
making it appear more like a square wave.
Printed Circuit Board Layout Suggestions
The EL driver’s high-frequency operation makes PCB
layout important for minimizing electrical noise. Keep the
IC’s GND pin and the ground leads of C1 and C
INT
less than
0.2in (5mm) apart. Also keep the connections to the COIL
pin as short as possible. To maximize output power and
efficiency and minimize output ripple voltage, use a ground
plane and solder the IC’s V
SS
pin directly to the ground
plane.
Lamp Effects
EL lamp parameters vary between manufacturers. Series
DC resistance, lighting efficiency and lamp capacitance
per area differ the most overall. Larger lamps require more
energy to illuminate. Lowering the oscillator frequency
allows more energy to be stored in the coil during each coil
switch cycle and increases lamp brightness. The oscillator
frequency can be lowered to a point where the lamp
brightness then begins to drop because the lamp fre-
quency must be above a critical frequency (approx. 100Hz)
to light. Lamp color is affected by the switching frequency
of the EL driver. Green EL lamps will emit a more blue light
as EL lamp frequency increases.
EL Lamp Driver Design Challenges
There are many variables which can be optimized for
specific applications. The amount of light emitted is a
function of the voltage applied to the lamp, the frequency at
which is applied, the lamp material, the lamp size, and the
inductor used. Zywyn supplies characterization charts to
aid the designer in selecting the optimum circuit configu-
ration.
Zywyn will perform customer application evaluations, using
the customer’s actual EL lamp to determine the optimum
operating conditions for specific applications. For custom-
ers considering an EL backlighting solution for the first
time, Zywyn is able to provide retrofits to non-backlit
products for a thorough electrical and cosmetic evaluation.
Please contact your local Zywyn sales representative or
the Zywyn factory directly to initiate this valuable service.
Noise Decoupling on Logic Inputs
If EL1/EL2 or ON/OFF are connected to traces susceptible
to noise, it may be necessary to connect bypass capacitor
of approximately 10nF between EL1/EL2 and V
SS
, and
ON/OFF and V
SS
. If these inputs are driven by a micropro-
cessor which provides a low impedance HIGH and LOW
signal, then noise bypassing may not be necessary.
Zywyn
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July 2005
rev. 03
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