SP4415 Datasheet, PDF (4/10 Pages) Sipex Corporation – Electroluminescent Lamp Driver with Selectable Level Outputs

The EL outputs can be enabled by driving the
Level Select pin (pin 7) high.
Four intensity levels can be set via the Level
Select pin (pin 7). The intensity levels correspond
with the number of coil pulses per bridge half
cycle. The full output is represented by 16 coil
pulses, levels 3, 2, 1 have 12, 9, and 7 coil pulses.
The coil pulses transfer energy to the EL lamp;
the more pulses per cycle, the brighter the lamp.
In order to set a level, the Level Select pin should
be driven high, then driven low (or released) and
within the next one second, the Level Select pin
should be again driven high; this sequence will
increment the level selection until the highest
level (level 4) is reached. The next sequence will
force the output back to the lowest intensity level,
level 1. The Level Select pin is equipped with a
debounce circuit such that momentary (≤15 mS)
opens of the input will not result in changes to the
output level.
The coil is an external component connected from
V_BATTERY to pin 3 of the SP4415. Energy is
developed in the coil according to the equation
E =1/2LI² where the current I is defined as
L
I=(V -IR-V )/R . In order to maximize the
BATTERY
OL T
energy produced by the coil, V
should
BATTERY
represent the largest voltage in the system (up to a
maximum of 6.0 v ); V_BATTERY= 3.0 VDC with a
35mH/125Ω coil is a typical example. It is not
necessary that V_DD=V_BATTERY. The majority of the
supply current is dissipated in the coil (10mA
typical). The SP4415 itself requires less than 1mA
(700µA typical). Coils are also a function of the
core material and winding used -- performance
variances may be noticeable from different coil
suppliers even though the values are the same. The
Sipex SP4415 is final tested using a 35mH/135
ohm coil. For suggested coil sources see page 8.
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 75% duty cycle square wave,
switching at 1/4 the oscillator frequency. For a
32,768 Hz oscillator f_COIL is 8,192Hz. 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 , the ground connection is switched
COIL
open, the field collapses and the energy in the
inductor is forced to flow toward the high voltage
H-bridge switches. f_COIL will send 16 of these charge
pulses 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 shorter (see figure 1 on page 7).
3 VDC
Coil
35mH/125Ω coil
32-64KHz
From crystal oscillator
1
NC
V
SS
CLK
Level
Select
Coil
V
DD
Lamp Lamp
Pushbutton level select
EL Lamp
Typical SP4415CN Application Circuit
SP4415DS/06
SP4415 Electroluminescent Lamp Driver
4
© Copyright 1996 Sipex Corporation