SP4426DS/01

SP4426 Electroluminescent Lamp Driver

© Copyright 1997 Sipex Corporation

3

THEORY OF OPERATION

The SP4426 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 1 and

Vss allows the user to vary the oscillator frequency.

The graphs on page 6 show the relationship between

C

coil inductance there will be an optimum C

valve that gives the maximum light output.

The suggested oscillator frequency is 20kHz

(C

divided to create two internal control signals, F

coil

and F

down by 8 flip flops, a 64kHz signal will be

divided into 8 frequency levels; 32kHz, 16kHz,

8kHz, 4kHz, 2kHz, 1kHz, .5kHz, .25 kHz. The

third flip flop output (8KHz) is used to drive the

coil (see figure 2 on page 8) and the eighth flip flop

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

the oscillator frequency can be varied to optimize

the lamp output, the ratio of F

equal 32.

The on-chip oscillator of the SP4426 can be

overdriven with an external clock source by

removing the C

clock source to pin 8. The clock should have a 50%

PIN DESCRIPTION

Pin 1— HON- Enable for driver operation,

high=active; low=inactive

Pin 2— N/C- No connect

Pin 3— Vss- Power supply common, connect to

ground.

Pin 4— N/C- No connect

Pin 5— Coil- Coil

Pin 6— D1- Diode cathode connection

Pin 7— EL1- Lamp driver output 1, connect to

EL lamp

Pin 8— EL2- Lamp driver output 2, connect to

EL lamp

Pin 9— N/C- No connect

Pin 10— N/C- No connect

Pin 11— Vdd- Power supply for driver, connect

to system Vdd.

Pin 12— C2- Capacitor input 2, connect to Cosc

Pin 13— N/C- No connect

Pin 14— C1- Capacitor input 1, connect to Cosc

5

6

7

10

9

8

1

2

3

4

14

13

12

11

SP4426 Schematic

Q

Q

Hon

SCR1

SCR2

OSC

FF1

FF6

coil

F

lamp

F

lamp

F

EL Lamp

1M

Ω

Vdd

Coil

7

8

EL1

EL2

Cap1

3

Vss

Vbattery

Vdd

11

5

9MH/35

Ω

1

180pF

IN4148

6

D1

.1

µF

C1

Optional

1,800pF

11

12

C2

Cap2