SP4425Q datasheet(3/12 Pages) SIPEX

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SP4425QDS/12

SP4425Q Electroluminescent Lamp Driver

THEORY OF OPERATION

The SP4425Q 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.

For a given choice of coil inductance there will be

an optimum C

OSC capacitor value that provides

maximum light output.

The suggested oscillator frequency is 28.8kHz

OSC=180pF). The oscillator output is internally

divided to create the control signal for f

LAMP. The

oscillator output is internally divided down by 6

flip flops. A 28.8kHz signal will be divided into 6

frequency levels: 14.4kHz, 7.2kHz, 3.6kHz,

1.8kHz, 900kHz, and 450Hz. The oscillator output

(28.8kHz) is used to drive the coil (see figure 2 on

page 6) and the sixth flip flop output (300Hz) is

used to drive the lamp. Although the oscillator

frequency can be varied to optimize the lamp

output, the ratio of f

COIL/fLAMP will always equal 64.

The coil is an external component connected from

BATTERY to pin 3 of the SP4425Q. VBATTERY= 3.0

VDC with a 2mH/44

Ω coil are typical conditions.

Energy is stored in the coil according to the equation

PIN DESCRIPTION

Pin 1 – C

OSC- Capacitor input 1, connect Capacitor

from V

SS to Pin 1 to set COSC frequency.

Pin 2 – V

SS- Power supply common, connect to

ground.

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

to pin 3.

Pin 4 – D1- Diode Cathode connection.

– C

INT- Integrator capacitor, connect capacitor

from pin 4 to ground to minimize coil glitch energy.

Pin 5 – Lamp- Lamp driver output2, connect to

EL lamp.

Pin 6 – Lamp- Lamp driver output1, connect to

EL lamp.

Pin 7 – V

DD- Power supply for driver, connect to

system V

DD.

Pin 8 – HON- Enable for driver operation,

high = active; low = inactive.

SP4425Q Schematic

HON

SCR1

SCR2

OSC

FF1

FF6

EL Lamp

Ω

VDD

Coil

EL2

EL1

Cap1

VSS

VBATTERY

VDD

2mH/44

Ω

180pF

IN4148

µF

COSC

Low ESR

decoupling

capacitor

CINT = 820pF typical

QR2

QR1

fCOIL

fLAMP

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