IMP528ESA datasheet(3/6 Pages) IMP

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IMP528

Electroluminescent Lamp Driver

Pin Descriptions

External Components

Pin Number

Name

Function

1VDD

Positive voltage supply for the IMP528. Inductor L may be connected here or to a

separate unregulated supply.

2RSW-OSC

Switch-mode resistor pin. Switching frequency is determined by an external resistor, RSW.

3CS

Boost converter storage capacitor. The voltage across the EL lamp is equal to twice the

voltage at CS.

4LX

Connection to flyback inductance, L.

GND

Ground pin.

6VB

EL lamp drive. The lamp is connected in a high-voltage bridge circuit with VB providing

the complementary connection to VA. The peak-to-peak AC voltage across the EL lamp is

thus two times VCS.

7VA

EL lamp drive. (See above)

8REL-OSC

The EL lamp oscillator frequency setting pin. The oscillator frequency is controlled

by external resistor REL.

External Component

Description and Selection Guide

Diode

Catch diode. A fast reverse recovery diode, with BV > 150V, such as an FDLL400 (150V).

Capacitor CS

This is the high voltage capacitor that stores the inductive energy transferred through the

catch diode. A capacitor with WV > 120V between 10nF and 100nF is recommended.

Resistor REL

The EL lamp oscillator frequency setting resistor. This resistor, connected between the

REL-OSC pin and VDD, provides an oscillator frequency inversely proportional to REL;

as REL increases, the EL lamp frequency decreases along with the current drawn by the lamp.

Lamp color is also determined by this frequency. A 2.7M

Ω resistor between the REL-OSC pin and

the VDD supply results in a lamp frequency around 250Hz.

Resistor RSW

Switching Oscillator frequency setting resistor. The switching oscillator resistor is connected

between the RSW-OSC pin and the VDD supply. The switching frequency is inversely proportional

to the resistor value, dropping as the resistance increases.

Inductor L

The inductor provides the voltage boost needed by means of inductive “flyback”. The internal

MOSFET switch alternately opens and closes the ground connection for the inductor at the

LX pin. When this internal switch opens, the inductor potential will forward-bias the catch

diode and the current will pass through the storage capacitor CS, charging it to a high voltage.

Smaller inductors are preferred to prevent saturation. As the value of the inductor

increases (and the series DC resistance of the inductor decreases), the switching frequency

set by RSW should be increased to prevent saturation. In general, smaller value inductors that

can handle more current are more desirable when larger area EL lamps must be driven.

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