SP4412ADS/12

SP4412ACN Electroluminescent Lamp Driver

© Copyright 2000 Sipex Corporation

3

THEORY OF OPERATION

The SP4412A is made up of three basic circuit

elements, a divider chain, a coil, and a switched

H-bridge network. The countdown chain

provides the circuit with a clock source used to

control the charge and discharge phases for the

coil and lamp. An external oscillator is required

and is delivered to pin 3 of the SO-8 package or

to the "Osc in" pad of the bare die. The chart on

page 6 shows the effect of variations in coil

values used. If a clock frequency other than

32kHz is used, the output of the driver as well as

the amount of current used, will be effected.

The suggested oscillator frequency is 32,768Hz.

This clock frequency is internally divided to

create two internal control signals, f

f

7 flip flops; therefore, a 32,768Hz signal will be

divided into the following frequencies; 32, 16,

8, 4, 2, 1, 0.5 and 0.25kHz. The second flip flop

output (8 kHz) is used to drive the coil (see

figure 2 on page 7) and the seventh flip flop

output (256 Hz) is used to drive the lamp.

Although the oscillator frequency can be varied

to optimize the lamp output, the ratio of f

f

PIN DESCRIPTION

Pin 1 – HON- Enable for driver operation,

high = active; low = inactive.

Pin 2 – NC

Pin 3 – Oscillator clock input

Pin 4 – V

ground.

Pin 5 – Coil - Coil input, connect coil from V

DD

to Pin 3.

Pin 6 – Lamp- Lamp driver output1, connect to

EL lamp.

Pin 7 – Lamp- Lamp driver output2, connect to

EL lamp.

Pin 8 – V

SP4412A Schematic

Q

Q

HON

FF1

FF2

EL Lamp

6

3

Coil

4

5

EL1

EL2

7

8

2

30 mH at 125

Ω

1

Clock

Divider

Chain

External

Clock

NC

1

2

3

4

8

7

6

5