®
SP4438
Ultra-Quiet Electroluminescent Lamp Driver
For Cellular Phone Applications
s
Patent Pending Output Waveshaping
s
Waveshaped Output Optimized For Low
Acoustic Noise And Maximum Efficiency
s
Reduced Supply Current And Standby
Current
s
Up to15cd/m
2
For Cell Phone Sized EL
Lamps (2 to 3 sq. in.)
s
Waveshaped Output And Low Frequency
Operation Minimize Stress On EL Lamp To
Extend Its Lifetime
s
Uses 820µH, Sub-2mm Coils
s
Gradual Rising And Falling Edges Minimizes
EMI
s
+2.7V To +3.3V Battery Operation
s
Space-Saving 8-pin MSOP package
APPLICATIONS
s
Cellular Radios
s
Wireless Communication Products
DESCRIPTION
The SP4438 device is a low noise, high voltage output DC-AC inverter designed to drive
electroluminescent lamps to backlight liquid crystal display and keypads used in cellular
phones, cordless phones, 2-way radios, and other wireless communication products. The
output waveform of the SP4438 device is ideal for cell phone applications requiring low
acoustic noise performance. One external resistor is used to set the internal oscillator
frequency and one inductor is required to generate the high voltage AC output to drive an EL
lamp up to 3 square inches in size. The SP4438 operates from a +3.0V battery source and
has a low power standby mode that draws less than 1µA, making it ideal for low-power cellular
applications. All input pins are ESD protected with internal diodes to V
DD
and V
SS
. The SP4438
is offered in a space-saving 8-pin MSOP package.
V
BATT
V
DD
1
ELEN 2
R
OSC
3
V
SS
4
SP4438
8
EL1
ELEN
2
L1
820µH/14Ω
7 EL2
6
5
C
INT
COIL
C1
0.1µF
C2
1nF
V
DD
R
OSC
714kΩ
1
R
OSC
3
4
SP4438
5
6
COIL
D1
1N4148
C
INT
8
V
SS
EL1
7
EL2
C
INT
47nF
EL Lamp
Rev.11/13/00
SP4438 Ultra-Quiet 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.
Supply Voltage (V
DD
to V
SS
)........................-0.3V, +5V
Operating Temperature.......................-40˚C to +85˚C
Storage Temperature........................-65˚C to +150˚C
Power Dissipation Per Package
8-pin MSOP
(derate 4.85mW/
O
C above +70
O
C).........................400mW
SPECIFICATIONS
V
DD
= +2.7V to +3.3V, L
COIL
= 820µH/14Ω, R
OSC
= 714kΩ, EL Lamp Load = (8nF + 2.5kΩ)/1MΩ, and T
AMB
= -40
O
C to +85
O
C. T
AMB
= 25
O
C for typical
values unless otherwise noted.
PARAMETER
INPUT CHARACTERISTICS
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
ELEN Input Impedance
Shutdown Current, I
SD
=I
COIL
+I
DD
INDUCTOR DRIVE
Coil Frequency, f
COIL
Coil Duty Cycle
Peak Coil Current, I
PK-COIL
EL LAMP OUTPUT
EL Lamp Frequency, f
LAMP
Peak to Peak Output Voltage, V
P-P
MIN.
TYP.
MAX.
UNITS
CONDITIONS
2.7
3.0
3.3
30
V
mA
V
V
DD
= +3.0V
V
DD
-0.25
V
DD
-0.25
1
0
V
DD
3
9
0.25V
V
DD
+0.25
V
MΩ
1
µA
V
ELEN
= LOW,V
DD
= +3.0V
26
23
32
43
45
kHz
%
R
OSC
= 714k
Ω
,T
AMB
= +25
O
C
T
AMB
= -40
O
C to +85
O
C,V
DD
= +3.0V
90
100
mA
190
175
130
120
250
336
348
Hz
T
AMB
= +25
O
C,V
DD
= +3.0V,with load
T
AMB
= -40
O
C to +85
O
C
T
AMB
= +25
O
C,V
DD
= +3.0V,with load
T
AMB
= -40
O
C to +85
O
C
T
AMB
= +25
O
C,V
DD
= +3.0V, NOTE 1
T
AMB
= +25
O
C,V
DD
= +3.0V,with load,
measured from 10% to 90%
145
140
26
V
P-P
dB
SPL
1.0
ms
Audible Noise
Rise Time
.55
0.8
NOTE 1:
Audible Noise is measured inside an acoustic sound chamber. The Sound Level Meter is a B&K
Mediator 2238, A-weighted with Condenser Mic type 4188 positioned 1/4 inch above the lamp in an 8 cubic inch
volume. See Figure 5 on page 6.
Rev. 11/13/00
SP4438 Ultra-Quiet Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
2
PINOUT
V
DD
1
ELEN 2
R
OSC
3
V
SS
4
SP4438
8
EL1
7 EL2
6
5
C
INT
COIL
PIN ASSIGNMENTS
Pin 1 — V
DD
— Positive Battery Power Supply.
Connect such that +2.7V < V
DD
< +3.3V.
Pin 2 — ELEN — Electroluminescent Lamp
Enable. When driven HIGH, this input pin
enables the EL driver outputs for EL1 and
EL2. This pin has an internal pulldown
resistor.
Pin 3 — R
OSC
— Oscillator Resistor. Connect-
ing a resistor to this input pin sets the fre-
quency of the internal clock.
Pin 4 — V
SS
— Power Supply Common. Con-
nect to the lowest circuit potential, typically
ground.
Pin 5 — COIL — The inductor for the EL lamp
is connected from V
DD
to this input pin.
Pin 6 — C
INT
— Integrating Capacitor. An
integrating capacitor (47nF typical) con-
nected from this pin to ground filters out any
coil switching spikes or ripple present in the
output waveform to the EL lamp. Connect-
ing a fast recovery diode from COIL to C
INT
increases the light output of the EL lamp.
Pin 7 — EL2 — Electroluminescent Lamp Out-
put 2. This is a high voltage lamp driver
output pin to connect to the EL lamp.
Pin 8 — EL1 — Electroluminescent Lamp Out-
put 1. This is a high voltage lamp driver
output pin to connect to the EL lamp.
Rev.11/13/00
SP4438 Ultra-Quiet Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
3
V
BATT
ELEN
2
L1
820µH/14Ω
SP4438
5
V
DD
R
OSC
714kΩ
1
6
R
OSC
3
4
C1
0.1µF
C2
1nF
V
SS
8
EL1
7
EL2
COIL
D1
1N4148
C
INT
C
INT
47nF
EL Lamp
Figure 1: Typical Operating Circuit for the SP4438.
Note: C1 should be close to L1.
Rev. 11/13/00
SP4438 Ultra-Quiet Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
4
V
BATT
V
DD
1
5 COIL
L1
820µH/14Ω
SP4438
R
OSC
714kΩ
R
OSC
3
OSC
D1
1N4148
6 C
INT
C
INT
47nF
C1
0.1µF
C2
1nF
PMOS
PMOS
Q
FF7
Q
ELEN 2
BRIDGE
CONTROL
DMOS
DMOS
4
V
SS
8
EL1
7
EL2
EL Lamp
Figure 2: Internal Block Diagram of the SP4438
Figure 3: EL Differential Output Waveform of the EL1 and EL2 Outputs of the SP4438
Rev.11/13/00
SP4438 Ultra-Quiet Electroluminescent Lamp Driver
© Copyright 2000 Sipex Corporation
5
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