MIC4832 datasheet(5/11 Pages) MICREL

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Micrel

MIC4832

November 2007

M9999-111507-B

Functional Diagram

Figure 1. MIC4832 Block Diagram

Functional Description

Overview

The MIC4832 is a high-voltage EL driver with an AC

output voltage of 220V peak-to-peak capable of

driving EL lamps up to 3 in

2. Input supply current for

the MIC4832 is typically 45µA reducing to 10nA in

shutdown. The high voltage EL driver has two

internal oscillators to control the switching MOSFET

and the H-bridge driver. Both of the internal

oscillators’

frequencies

can

individually

programmed through the external resistors to

maximize the efficiency and the brightness of the EL

lamp.

Regulation

Referring to Figure 1, initially power is applied to

VDD. The internal feedback voltage is less than the

reference voltage causing the internal comparator to

go low which enables the switching MOSFET’s

oscillator. When the switching MOSFET turns on,

current flows through the inductor and flows into the

switch. The switching MOSFET will typically turn on

for 90% of the switching period. During the on-time,

energy is stored in the inductor. When the switching

MOSFET turns off, current flowing into the inductor

forces the voltage across the inductor to reverse

polarity. The voltage across the inductor rises until

the external diode conducts and clamps the voltage

at VOUT + VD1. The energy in the inductor is then

discharged into the COUT capacitor. The internal

comparator continues to turn the switching MOSFET

on and off until the internal feedback voltage is

above the reference voltage. Once the internal

feedback voltage is above the reference voltage, the

internal

comparator

turns

off

the

switching

MOSFET’s oscillator.

When the EL oscillator is enabled, VA and VB switch

in opposite states to achieve a 220V peak-to-peak

AC output signal. The external resistor that connects

to the REL pin determines the EL frequency.

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