SP4422ADS/15

SP4422A Electroluminescent Lamp Driver

© Copyright 2000 Sipex Corporation

3

THEORY OF OPERATION

The SP4422A is made up of three basic circuit

elements, an oscillator, coil, and switched H-bridge

network. The oscillator provides the device with

an on-chip clock source used to control the charge

and discharge phases for the coil and lamp. An

external capacitor connected between pins 7 and 8

allows the user to vary the oscillator frequency

from 32kHz to 400kHz. The graphs on page 6

show the relationship between C

output voltage. In general, increasing the C

OSC

capacitor will increase the lamp output.

The suggested oscillator frequency is 90kHz

(C

divided to create two internal control signals, f

COIL

and f

down by 8 flip flops, a 90kHz signal will be

divided into 8 frequencies; 45kHz, 22.5kHz,

11.2kHz, 5.6kHz, 2.8kHz, 1.4kHz, 703Hz, and

352Hz. The third flip flop output (8kHz) is used to

drive the coil (see figure 2 on page 9) and the

eighth flip flop output (250Hz) is used to drive the

lamp. Although the oscillator frequency can be

varied to optimize the lamp output, the ratio of

f

The on-chip oscillator of the SP4422A can be

overdriven with an external clock source by

removing the C

PIN DESCRIPTION

Pin 1 – HON- Enable for driver operation,

high = active; low = inactive.

Pin 2 – V

ground.

Pin 3 – Coil- Coil input, connect coil from V

DD

to pin 3.

Pin 4 – Lamp- Lamp driver output2, connect to

EL lamp.

Pin 5 – Lamp- Lamp driver output1, connect to

EL lamp.

Pin 6 – V

system V

Pin 7 – Cap1- Capacitor input 1, connect to C

Pin 8 – Cap2- Capacitor input 2, connect to C

1

2

3

4

8

7

6

5

Q

Q

HON

SCR1

SCR2

OSC

FF1

FF2

EL Lamp

Coil

4

5

EL2

EL1

7

8

Cap1

Cap2

2

6

3

5mH/18

Ω

1

0.1

µF

SP4422A Schematic