SP4405 datasheet(4/20 Pages) SIPEX

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SP4405DS/18

SP4405 Low Voltage Electroluminescent Lamp Driver

DESCRIPTION

The SP4405 Electroluminescent Lamp Driver

is a low-cost low voltage device ideal for the

replacement of LED backlighting designs in

keypads, handsets, PDAs and other portable

designs. The SP4405 contains a DC-AC inverter

that can produce an AC output of 160V

PP (typical)

from a +2.2V to +4.5V input voltage. An

internal feedback loop regulates the lamp voltage

output to 160V

PP (typical) with varying supply

voltages to maintain constant EL lamp

brightness. An internal block diagram of the

SP4405 can be found in Figure 1.

The SP4405 is built on Sipex's dielectrically

isolated BiCMOS process that provides the

isolation required to separate the high voltage

AC signal used to drive the EL lamp from the

low voltage logic and signal processing circuitry.

This ensures latch-up free operation in the

interface between the low voltage CMOS

circuitry and the high voltage bipolar circuitry.

A total of only six external components are

required for the standard operation of the

SP4405: an inductor, a fast recovery diode,

three capacitors and a resistor. A diagram of the

SP4405 in a typical application can be found in

Figure 2.

Electroluminescent Technology

An EL lamp is basically a strip of plastic that is

coated with a phosphorous material which emits

light (fluoresces) when a high voltage (>40V)

which was first applied across it, is removed or

reversed. Long periods of DC voltages applied

to the material tend to breakdown the material

Figure 1. Internal Diagram of the SP4405

fCOIL

fLAMP

FF7

VBATTERY

470

µH, 3Ω

EL Lamp

SCR1

SCR2

VSS

CINT

COIL

EL2

EL1

CINT

0.1

µF

OSC

ROSC

450k

Ω

VREF=1.25V

ELEN

ERROR

COMPARATOR

SP4405

0.1

µF

1N4148

VDD

ROSC 8

1nF

NOTES: * Optional Component

** C

INT may be decreased to change the square wave output to a sawtooth waveform.

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