SP4415DS/06

SP4415 Electroluminescent Lamp Driver

© Copyright 1996 Sipex Corporation

4

Typical SP4415CN Application Circuit

1

V

SS

Coil

Lamp

V

DD

Lamp

Level

Select

CLK

32-64KHz

From crystal oscillator

Pushbutton level select

EL Lamp

3 VDC

Coil

35mH/125

Ω coil

NC

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

developed in the coil according to the equation

E

I=(V

energy produced by the coil, V

represent the largest voltage in the system (up to a

maximum of 6.0 v ); V

35mH/125

Ω coil is a typical example. It is not

necessary that V

supply current is dissipated in the coil (10mA

typical). The SP4415 itself requires less than 1mA

(700

µA 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

end of the coil at pin 3 to ground or to open circuit.

The f

switching at 1/4 the oscillator frequency. For a

32,768 Hz oscillator f

time when the f

connected from V

magnetic field is created in the coil. During the low

part of f

open, the field collapses and the energy in the

inductor is forced to flow toward the high voltage

H-bridge switches. f

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).