ZSP4425 Electroluminescent Lamp Driver
Zywyn
Features
• Low voltage, single battery operation
(1.1VDC < V
BATTERY
< 1.7VDC), or
(2.2VDC < V
BATTERY
< 4.5VDC)
• DC to AC inverter for EL backlit display panels
• Externally adjustable internal oscillator
• Low current standby mode
ZSP4425
Electroluminescent Lamp Driver
For 1.5V or 2.2V to 4.5V Applications
General Description
The ZSP4425 is a high voltage output DC-AC converter that can
operate from a single +1.5VDC, +3.0VDC, or +2.2VDC to
+4.5VDC power supply. The ZSP4425 is designed with our
proprietary high voltage BiCMOS technology and capable of
supplying up to 220V
PP
signals, making it ideal for driving
electroluminescent lamps. The device features 1μA (typical)
standby current for use in low power portable products. One
external inductor is required to generate the high voltage charge
and one external capacitor is used to select the oscillator and
lamp frequencies. The ZSP4425 is offered in both 8-pin narrow
SOIC and 8-pin MSOP package. For delivery in die form, please
consult the factory.
Applications
•
•
•
•
•
Pagers
Digital watches
MP3 players
Cell Phones
Backlit LCD displays
Ordering Information
Part Number
ZSP4425CN
ZSP4425LCN
Temperature Range
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
0°C to +70°C
0°C to +70°C
n/a
n/a
Package Type
8-Pin nSOIC
8-Pin nSOIC Green
8-Pin MSOP
8-Pin MSOP Green
Die in Wafflepack
Die in Wafer Form
nSOIC Eval. Board
MSOP Eval. Board
Pin Configuration
ZSP4425CU
ZSP4425LCU
ZSP4425CX
ZSP4425CW
ZSP4425NEB
ZSP4425UEB
C
OSC
1
V
SS
2
COIL 3
D1 4
8
HON
V
DD
EL1
EL2
Zywyn
ZSP4425
7
6
5
Please contact the factory for pricing, availabiliy on Tape-and-Reels,
and Green Package
options.
8-Pin nSOIC/MSOP
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 Corporation • Tel (408) 733-3225 • Fax (408) 733-3206 • Email sales@zywyn.com • www.zywyn.com
specifications subject to change without notice
October 2005
rev. 04
Zywyn Corporation
ZSP4425
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 (pin 3).......................................................100mA
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
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
= +1.5V, C
LAMP
= 8200pF with 100Ω series resistance, Coil = 470μH at 4Ω, C
INT
= 1800pF, C
OSC
= 180pF, unless
otherwise noted.
Symbol
V
DD
I
COIL
V
COIL
V
HON
Parameter
Supply Voltage
Supply Current
Coil Voltage
HON Input Voltage
LOW: EL off
HIGH: EL on
HON+V
DD
Current
Shutdown Current
Coil Frequency
Coil Duty Cycle
I
PK-COIL
EL LAMP OUTPUT
f
LAMP
V
PP
EL Lamp Frequency
Peak-to-Peak Output Voltage
T
A
= +25°C, V
DD
= +1.5V
T
A
= +25°C, V
DD
= +1.5V
250
120
400
160
600
Hz
V
Peak Coil Current
Guaranteed by design
HON ties to V
DD
Condition
HON ties to V
DD
; See Figure 2
V
HON
= V
DD
= +1.5V
Min
1.1
Typ
1.5
30
1.1
– 0.25
1.1
0
1.5
Max
1.7
60
1.7
0.25
1.7
3
1
25.6
90
90
5
Units
V
mA
V
V
I
HON
+ I
DD
I
SD
= I
COIL
INDUCTOR DRIVE
f
COIL
= f
LAMP
X 64
Internal pull-down,
V
HON
= V
DD
= +1.5V; See Figure 2
V
HON
= V
DD
= 0V: V
COIL
= +1.5V
mA
μA
kHz
%
mA
Zywyn
2
October 2005
rev. 04
Zywyn Corporation
ZSP4425
Electrical Characteristics
T
A
= +25°C, V
DD
= +3.0V, C
LAMP
= 4nF with 100Ω series resistance, Coil = 2mH at 44Ω, C
INT
= 470pF, C
OSC
= 180pF, 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
Coil Frequency
Coil Duty Cycle
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
300
120
170
450
150
190
600
Hz
V
V
Peak Coil Current
Guaranteed by design
Internal pull-down,
V
HON
= V
DD
= +3.0V; See Figure 4
V
HON
= 0V
V
HON
= V
DD
= +3.0V
V
DD
– 0.25
V
DD
– 0.25
0
V
DD
5
1
28.8
90
90
Condition
Min
2.2
Typ
3.0
28
Max
4.5
35
4.5
0.25
V
DD
+ 0.25
20
8
Units
V
mA
V
V
I
HON
I
SD
= I
COIL
+ I
DD
INDUCTOR DRIVE
f
COIL
= f
LAMP
X 64
μA
μA
kHz
%
mA
Bonding Diagram
HON
V
DD
EL1
C
OSC
EL2
D1
76 x 46
MS133
Notes:
1. Mask number is MS133.
2. Die size is 76 x 46 mils.
3. Die thickness is 11 mils +/- 1.
4. Bonding pads are 125 x 125 microns.
5. Die substrate down-bonds to Vss (GND).
Coil
V
SS
Die Photo
Zywyn
3
October 2005
rev. 04
Zywyn Corporation
ZSP4425
Block Diagram
V
BATTERY
Connects to V
BATTERY
or to microcontroller
>
control output
0.1μF
Low ESR
decoupling
capacitor
470μH/4Ω
1N4148
3
Coil
4
C
INT
= 1800pF (typ)
7
V
DD
OSC
Cap1
1MΩ
8
HON
D1
1
C
OSC
= 180pF
f
COIL
HV
1
HV
2
f
LAMP
Q
FF1
FF2
Q
f
LAMP
EL2
5
EL Lamp
EL1
6
V
SS
2
Figure 1. Block Diagram
Pin Description
Pin Number
1
2
3
4
5
6
7
8
Pin Name
C
OSC
V
SS
COIL
D1
EL2
EL1
V
DD
HON
Pin Function
Capacitor input 1: Connect capacitor from V
SS
to this pin to set C
OSC
frequency.
Power supply common: Connect to ground.
Coil input: Connect coil from V
DD
to this pin.
Diode Cathode connection: C
INT
(Integrator capacitor), connect capacitor
from this pin to ground to minimize coil glitch energy.
Lamp driver output 2: Connect to EL lamp.
Lamp driver output 1: Connect to EL lamp.
Power supply for driver: Connect to system V
BATTERY
for 2.2~4.5V operation,
or tie with HON pin together connects to system V
BATTERY
for 1.5V operation.
Enable for driver operation: high = active; low = inactive.
Zywyn
4
October 2005
rev. 04
Zywyn Corporation
ZSP4425
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. 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 lamp. f
COIL
will send 32 of these charge
pulses (see
Figure 6)
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 5).
The H-bridge consists of two proprietary low on-resistance
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 64. For a 25.6kHz oscilla-
tor, f
LAMP
= 400Hz. When the energy from the coil is
released, a high voltage spike is created triggering the
high voltage switches. The direction of current flow is
determined by which high voltage is enabled. One full
cycle of the H-bridge will create a voltage step from ground
to 80V (typical) on pins 5 and 6 which are 180 degrees out
of phase with each other (see
Figure 7).
A differential view
of the outputs is shown in
Figure 8.
Circuit Description
The ZSP4425 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 1 and V
SS
allows the user to vary the oscillator
frequency. For a given choice of coil inductance there will
be an optimum C
OSC
capacitor value that gives the maxi-
mum light output.
The suggested oscillator frequency is 25.6kHz (C
OSC
=180pF). The oscillator output is internally divided to
create the control signal for f
LAMP
. The oscillator output is
internally divided down by 6 flip-flops, a 25.6kHz signal will
be divided into 6 frequency levels: 12.8kHz, 6.4kHz, 3.2kHz,
1.6kHz, 800Hz, and 400Hz. The oscillator output (25.6kHz)
is used to drive the coil (see
Figure 2)
and the sixth flip-
flop output (300Hz) 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 64.
The coil is an external component connected from
V
BATTERY
to pin 3 of the ZSP4425. V
BATTERY
=+1.5VDC
with a 470μH/4Ω coil are typical conditions. Energy is
stored in the coil according to the equation E
L
=1/2(LI)
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 param-
eters of the application such as V
BATTERY
, L, R
L
, 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 majority of the current goes through the coil and
typically less than 2mA is required for V
DD
of the ZSP4425.
V
DD
can range from +1.5V, or +2.2V to +4.5V; it is not
necessary that V
DD
= V
BATTERY
. Coils are also a function of
the core material and winding used — performance vari-
ances may be noticeable from different coil suppliers. The
Zywyn ZSP4425 is final tested at 1.5V using a 470μH/4Ω
coil from Toko, and a 2mH/44Ω coil from Matsushita at +3V.
For suggested coil sources, see
“Coil Manufacturers.”
Layout Considerations
The ZSP4425 circuit board layout must observe careful
analog precautions. For applications with noisy power
supply voltages, 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.
Integrator Capacitor
An integrating capacitor must be placed from pin 4 (D1) to
ground in order to minimize glitches associated with switch-
ing the coil. A capacitor at this point will collect the high
voltage spikes and will maximize the peak-to-peak voltage
output. High resistance EL lamps will produce more pro-
nounced spiking on the EL output waveform; adding the
C
INT
capacitor will minimize the peaking and increase the
voltage output at each coil step. The value of the integrator
capacitor is application specific typical values can range
from 500pF to 0.1μF. No integrator capacitor or very small
values (500pF) will have a minor effect on the output,
whereas a 0.1μF capacitor will cause the output to charge
and discharge rapidly creating a square wave output. For
most applications an 1800pF integrator capacitor is suit-
able.
Zywyn
5
October 2005
rev. 04
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