11-14-00
SP4501 EL Plus Piezo Driver
Copyright 2000 Sipex Corporation
1
s
Integrated EL Plus Piezo Driver For
Portable Electronic Devices
s
Reduces System Cost, Size & Compo-
nent Count
s
+2.2V to +6.0V Battery Operation
s
A Single External Coil Drives Both the
EL Lamp and Piezotransducer Circuitry
s
Piezotransducer Can Be Driven By an
External Clock or Internal Clock
s
A Single Resistor Controls the Internal
Oscillator
s
DC-to-AC Inverter Produces Up To
200V
P-P
to Drive EL Lamps
s
DC-to-AC Inverter Produces Waveform
to Drive Piezotransducer
s
Low Current Standby Mode Draws Less
than 1
A
DESCRIPTION
The SP4501 provides designers with both an electroluminescent lamp driver for backlighting and
a piezotransducer driver to generate audio alert tones. The integration of an EL lamp driver and
a piezotransducer driver in a single cost-effective IC reduces system cost, board space
requirements and component count. The SP4501 is ideal for portable applications such as
pagers, electronic games, PDAs, medical equipment, and designs with liquid crystal displays,
keypads, and backlit readouts. The SP4501 will operate from a +2.2V to +6.0V source. The
device features a low power standby mode which draws less than 1
A (typical). The frequency
of the internal oscillator is set with a single external resistor. The piezotranducer driver can be
driven with the internally generated clock signal or an external clock signal provided by the
designer. A single inductor is required to generate the high voltage AC used to drive the EL lamp
and the piezotransducer. All input pins are ESD protected with diodes to V
DD
and V
SS
.
EL Plus Piezo Driver
ELEN
PZEN
R
OSC
PZCK
V
DD
EL2
EL1
PZ2
1
2
3
4
11
12
13
14
PZCK
no connect
V
SS
5
6
7
PZ1
COIL
8
9
10
CAP
SP4501
SP4501
APPLICATIONS
s
PDA's
s
Pagers
s
GPS
s
Hand Held Medical Devices
11-14-00
SP4501 EL Plus Piezo Driver
Copyright 2000 Sipex Corporation
2
SPECIFICATIONS
V
DD
= +3.0V, L = 470
H, C
LAMP
= 8nF, C
PZ
= 16nF, CINT = 1800pF R
OSC
= 500k
, and T
AMB
= 25C unless otherwise noted.
STORAGE CONSIDERATIONS
Storage in a low humidity environment is preferred.
Large high density plastic packages are moisture sen-
sitive 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 environment 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. Sipex ships prod-
uct in Dry Vapor Barrier Bags with a humidity indicator
card and desiccant pack. The humidity indicator should
be below 30%RH.
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.
Power Supply, V
DD
.................................................7.0V
Input Voltages, Logic.....................-0.3V to (V
DD
+0.3V)
Lamp Outputs...................................................220V
P-P
Operating Temperature.........................-40C to +85C
Storage Temperature..........................-65C to +150C
Power Dissipation Per Package
14-pin SOIC
(derate 8.33mW/C above +70C)....................700mW
14-pin TSSOP
(derate 9.96mW/C above +70C)....................800mW
The information furnished 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 become
part of the terms and conditions of any subsequent
sales agreement with Sipex. Specifications are subject
to change without 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.
R
E
T
E
M
A
R
A
P
.
N
I
M
.
P
Y
T
.
X
A
M
S
T
I
N
U
S
N
O
I
T
I
D
N
O
C
V
,
e
g
a
t
l
o
V
y
l
p
p
u
S
D
D
2
.
2
0
.
3
0
.
6
V
,
t
n
e
r
r
u
C
y
l
p
p
u
S
I
L
I
O
C
I
+
D
D
8
2
8
4
0
9
A
m
L
L
I
O
C
0
7
4
=
F
t
n
e
r
r
u
C
y
b
d
n
a
t
S
1
.
0
A
r
o
f
e
g
a
t
l
o
V
t
u
p
n
I
K
C
Z
P
,
K
C
Z
P
,
N
E
Z
P
d
n
a
N
E
L
E
W
O
L
H
G
I
H
5
7
.
2
0
0
.
3
5
2
.
0
V
e
c
n
a
d
e
p
m
I
t
u
p
n
I
K
C
Z
P
d
n
a
N
E
L
E
K
C
Z
P
d
n
a
N
E
Z
P
1
M
V
N
E
L
E
V
0
=
e
v
i
r
D
r
o
t
c
u
d
n
I
f
,
y
c
n
e
u
q
e
r
F
li
o
C
C
S
O
0
.
7
3
7
.
5
4
7
.
4
5
z
H
k
f
f
o
e
l
c
y
C
y
t
u
D
C
S
O
0
9
%
t
n
e
r
r
u
C
li
o
C
k
a
e
P
0
0
1
A
m
t
u
p
t
u
O
r
e
v
i
r
D
o
z
e
i
P
/
p
m
a
L
L
E
V
,
e
g
a
t
l
o
V
t
u
p
t
u
O
o
z
e
i
P
Z
P
5
2
V
f
o
z
e
i
p
;
H
G
I
H
=
N
E
Z
P
,
z
H
k
1
.
3
=
T
B
M
A
5
2
+
=
O
C
T
B
M
A
0
4
-
=
O
5
8
+
o
t
C
O
C
V
,
e
g
a
t
l
o
V
t
u
p
t
u
O
p
m
a
L
L
E
0
1
1
V
T
B
M
A
5
2
+
=
O
C
T
B
M
A
0
4
-
=
O
5
8
+
o
t
C
O
C
f
,
y
c
n
e
u
q
e
r
F
p
m
a
L
L
E
P
M
A
L
9
8
2
7
5
3
7
2
4
z
H
T
B
M
A
5
2
+
=
O
C
T
B
M
A
0
4
-
=
O
5
8
+
o
t
C
O
C
f
,
y
c
n
e
u
q
e
r
F
o
z
e
i
P
Z
P
3
.
2
9
.
2
4
.
3
z
H
k
;
H
G
I
H
=
N
E
Z
P
T
B
M
A
5
2
+
=
O
C
T
B
M
A
0
4
-
=
O
5
8
+
o
t
C
O
C
1.0
11-14-00
SP4501 EL Plus Piezo Driver
Copyright 2000 Sipex Corporation
3
Electroluminescent Technology
An EL lamp consists of a thin layer of phospho-
rous 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, transistors
and several resistors and capacitors. This ap-
proach is large and bulky and cannot be imple-
mented in most handheld equipment. Sipex
offers low power single chip driver circuits spe-
cifically designed to drive small to medium sized
electroluminescent panels. Sipex EL drivers
provide a differential AC voltage without a DC
offset to maximize EL lamp lifetime. The only
additional 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 undesirable "hot spots" in
the display. Also, an EL lamp typically con-
sumes less power that LED's or incandescent
bulbs in similar lighting situations. These fea-
tures make EL ideal for attractive, battery pow-
ered products.
THEORY OF OPERATION
Coil Switch
The SP4501 has an inductor-based boost con-
verter to generate the high voltage used to drive
the EL lamp. Energy is stored in the inductor
according to the equation E
L
= 1/2 (LI
pk
2
) where
I
pk
= (t
ON
) (V
BATT
- V
CEsat
) /L. An internal oscilla-
tor 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
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 internal 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 become 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 suggested coil
suppliers refer to page 10.
Oscillator
The internal oscillator generates a high frequency
clock used by the boost converter and H-Bridge.
An external resistor from VDD to ROSC sets the
oscillator frequency. Typically a 500k
resistor
sets the frequency to 45.7kHz. The high fre-
quency 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 fre-
quency. The high frequency clock is divided by
16 to create a medium frequency clock to drive
the piezo H-Bridge. The oscillator has low
sensitivity to temperature and supply voltage
variations, increasing the performance of the EL
driver over the operating parameters.
Dual H-Bridge
The H-Bridge consists of two SCR structures
and two NPN transistors that control how the
lamp is charged. Setting ELEN to HIGH acti-
vates the EL H-Bridge. The EL driver illumi-
nates the lamp by applying the high voltage
supply of the boost converter to the lamp termi-
nals 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 necessary to adequately
illuminate the EL lamp. The piezo driver output
applies an AC voltage to the piezotransducer in
a similar manner. The piezo driver operates in
two modes.
11-14-00
SP4501 EL Plus Piezo Driver
Copyright 2000 Sipex Corporation
4
A logic HIGH on pin PZEN will enable the piezo
driver and apply a waveform to the
piezotransducer until PZEN is released. This
waveform will produce a tone that is 1/16 the
frequency of the internal oscillator. Alternately,
an external clock applied to PZCK or PZCK pins
will enable the piezo driver and generate a tone
at the applied clock frequency.
The external applied clock frequency should be
greater than f
osc
/64. To put the circuit in an
inactive state it is required that PZCK remain at
logic LOW and PZCK remain at logic HIGH.
The piezo driver and the EL driver may be
operated simultaneously but with decreased light
output from the EL panel.
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 resis-
tance. Since small coils (<1mH) have inherently
low series DC resistance, the current can peak
dramatically through a small coil during satura-
tion. This situation results in wasted energy not
stored in the magnetics of the coil but expressed
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.
Lamp Effects
EL lamp parameters vary between manufactur-
ers. 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 frequency 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.
Noise Decoupling on Logic Inputs
If ELEN, PZEN, PZCK or PZCK are connected
to traces susceptible to noise, it may be necessary
to connect bypass capacitors of approximately
10nF between ELEN and VSS, PZEN and VSS,
PZCK and VSS, and PZCK and VDD. If these
inputs are driven by a microprocessor which
provides a low impedance HIGH and LOW
signal, then noise bypassing may not be neces-
sary. If some inputs are unused (as PZCK and
PZCK may be) then these inputs should be tied
to the power supply that sets the input to an
inactive state.
Increasing Light Output
EL lamp light output can be improved by con-
necting 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 experimentation. A
rule of thumb is larger coils (1mH) are paired
with a smaller C
INT
(680pF) and smaller coils
(470
H) 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 capaci-
tance of the integration capacitor, C
INT
, will inte-
grate the sawtooth waveform making it
11-14-00
SP4501 EL Plus Piezo Driver
Copyright 2000 Sipex Corporation
5
appear more like a square wave.
Printed Circuit Board Layout Sugges-
tions
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 volt-
age, use a ground plane and solder the IC's VSS
pin directly to the ground plane.
EL Lamp Driver Design Challenges
There are many
variables which can be opti-
mized 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. Sipex supplies characterization charts to
aid the designer in selecting the optimum circuit
configuration.
Sipex will perform customer application evalu-
ations, using the customer's actual EL lamp to
determine the optimum operating conditions for
specific applications. For customers consider-
ing an EL backlighting solution for the first time,
Sipex is able to provide retrofits to non-backlit
products for a thorough electrical and cosmetic
evaluation. Please contact your local Sipex sales
Representative or the Sipex factory directly to
initiate this valuable service.
PDF 
ZIP