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SP4426 Datasheet(PDF) 4 Page - Sipex Corporation

Part No. SP4426
Description  Electroluminescent Lamp Driver with High Output Drivers
Download  11 Pages
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Maker  SIPEX [Sipex Corporation]
Homepage  http://www.sipex.com
Logo SIPEX - Sipex Corporation

SP4426 Datasheet(HTML) 4 Page - Sipex Corporation

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SP4426DS/01
SP4426 Electroluminescent Lamp Driver
© Copyright 1997 Sipex Corporation
4
duty cycle and range from Vdd-1V 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 9 of the SP4426. Energy is stored in
the coil according to the equation E
L=1/2LI
2 where
I, the the first approximation is (V
bat-VCE)RL. Where
V
CE is approximately ) 0.5 volts for the internal coil
driver transistor, and R
L is the series resistance of
the inductor. In order to maximize the energy
stored in the inductor and subsequently recovered
during the switching off of the coil transistor, it
is expedient to use the highest value battery,
the largest inductor with the smallest series
resistance that the system constraints will permit.
This energy recovery is directly related to the
brightness of the lamp output. There are great
variations among coils; caused by magnetic
material differences, winding differences and
parasitic capacitance. The Sipex SP4426 is final
tested using a 9mH/35
Ω coil from Hitachi. For
suggested coil sources see page 8.
The supply Vdd can range from 2.2 to 6.0V. It is
not necessary that Vdd=V
battery. Vbattery should not
exceed max coil current specification. The
majority of the current goes through the coil and is
typically much greater than Idd.
Optional
1800pF
Cosc
Coil
D1
EL1
Vdd
N/C
N/C
EL2
Switch
3 Volt
Battery
+
-
N/C
C2
Vss
N/C
N/C
C1
HON
6 SQ. IN.
EL LAMP
1
IN418
180pF
The F
coil signal controls a switch that connects the
end of the coil at pin 5 to ground or to open circuit.
The F
coil signal is a 94% 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 16 of these
charge pulses (see figure 2 page 8) 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 1 page 8).
For maximum performance a fast recovery diode
is recommended and should be connected between
pins 5 and 6 (cathode side). The low reverse
voltage capacitance of the fast recovery diode
minimizes the voltage that is charged and
discharged across it and this increases the energy
transferred to the lamp.
The H-bridge consists of two SCR structures that
act as high voltage switches. These two switches
control the polarity of how the lamp is charged.
The SCR switches are controlled by the F
lamp signal
which is the oscillator frequency divided by 64.
For a 20kHz oscillator, F
lamp=300Hz.
PDA Application
Typical SP4426 Application Circuit


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