SP4416 Datasheet, PDF (4/13 Pages) Sipex Corporation – Electroluminescent Lamp Driver with 4-Level Light Intensity Selection Feature

FUNCTIONAL DESCRIPTIONS
Oscillator Section
The SP4416 uses an internal oscillator circuit that
has the frequency set by C . The oscillator
OSC
produces a 32kHz clock signal used internally and
is divided down to create f_COIL and f_LAMP. The ratio
of the coil frequency (f ) and the H-bridge
COIL
(f ) is fixed.
LAMP
Intensity Setting
As with the SP4415, the SP4416 incorporates an
intensity select pin that will select one of four light
output intensity levels. The ENLI pin serves as
both an enable function and level select. This pin
is edge triggered and enables on the rising edge or
LOW-HIGH transition. The ENLI input is not
debounced requiring chatterless ENLI transitions.
In order to set a level, the ENLI pin should be
asserted with a logic HIGH, and then asserted with
a logic LOW. An internal pull-down resistor will
keep the EL driver disabled unless defined by a
logic HIGH. To increment the intensity sequence,
the ENLI should be asserted with another LOW-
HIGH transition within the next 800µS in order to
step to the next light intensity. From power-up, the
first enable high will produce 100% of the output.
The next LOW-HIGH transition will start the
output back at the first level of intensity. The next
set of four LOW-HIGH transitions will increment
the output to the highest intensity at 100%. If set to
a desired intensity, the ENLI pin should remain
HIGH to maintain the desired intensity. Refer to
Figure 6 for a timing diagram.
A time greater than 8ms between the falling edge
of the previous transition to the next ENLI transition
will leave the EL driver output disabled until a
logic HIGH is asserted back into the ENLI pin.
A timing less than 800µs between the falling edge
of the previous transition to the next ENLI transition
will increment to the next output intensity. Refer to
Figure 7 for timing diagram.
When the ENLI sees the next LOW-HIGH
transition, longer than 8ms, the output will revive
to the output intensity (VPEAK) just before being
disabled. Refer to Figure 8 for timing diagram.
Coil
As in our other EL drivers, the SP4416 uses the
coil to generate current to drive the H-bridge.
Energy is stored in the coil according to the equation
E_L = 1/2LI_P2 where I_P, to the first approximation, is
the product I_P = (t_ON)(V_BATTERY - V_CE)/L), where t_ON
is the time it takes for the coil to reach its peak
current, V_CE is the voltage drop across the internal
NPN transistor for f_COIL, and L is the inductance of
the coil. When the NPN transistor switch is off, the
energy is forced through an internal diode which
drives the switched H-bridge network. This energy
recovery is directly related to the brightness of the
EL lamp output.
The f signal controls a switch that connects the
COIL
end of the coil at pin 6 to ground or to open circuit.
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. When
the f_COIL signal is LOW, the ground connection is
switched open, the field collapses, and the energy
in the inductor is forced to flow toward the high
voltage H-bridge switches. As a result, charge
pulses are delivered to the lamp at a rate defined by
f_COIL. Each pulse increases the voltage drop across
the lamp in discrete steps. As the voltage potential
approaches its maximum, the steps become smaller.
The preferred coil has a typical height of 2.0mm
and a maximum height of 2.2mm. The Toko D52FU
family with part number 875FU-272M, which offers
a 2.7mH/45ohm coil that complies with the
height requirement.
H-Bridge
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 32. When the energy from the coil is released,
a high voltage spike is created triggering the
SCR switches. The direction of current flow is
determined by which SCR is enabled.
SP4416DS/06
SP4416 Electroluminescent Lamp Driver with 4-Level Light Intensity Selection Feature
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© Copyright 1999 Sipex Corporation