SP4416DS/06

SP4416 Electroluminescent Lamp Driver with 4-Level Light Intensity Selection Feature

© Copyright 1999 Sipex Corporation

4

FUNCTIONAL DESCRIPTIONS

Oscillator Section

The SP4416 uses an internal oscillator circuit that

has the frequency set by C

produces a 32kHz clock signal used internally and

is divided down to create f

of the coil frequency (f

(f

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 800

µS 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 800

µs 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

the product I

is the time it takes for the coil to reach its peak

current, V

NPN transistor for f

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

end of the coil at pin 6 to ground or to open circuit.

During the time when the f

coil is connected from V

charged magnetic field is created in the coil. When

the f

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

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.