MIC4832 datasheet(8/22 Pages) MICROCHIP

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MIC4832

DS20006163B-page 8



2019 - 2022 Microchip Technology Inc.

4.0

FUNCTIONAL DESCRIPTION

4.1

Overview

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

output voltage of 220V peak-to-peak that’s capable of

driving EL lamps up to 3 in2. Input supply current for the

MIC4832 is typically 45 µA, reducing to 10 nA 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 be individually programmed through

the external resistors to maximize the efficiency and

the brightness of the EL lamp.

4.2

Regulation

Referring to the Functional Block Diagram, initially

power is applied to VDD. The internal feedback voltage

is less than the reference voltage, causing the internal

comparator to go high, which then 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.

FIGURE 4-1:

100 Hz Output Waveform

4.3

Switching Frequency

The switching frequency of the converter is controlled

via an external resistor between the RSW pin and VDD

pin of the device. The switching frequency increases as

the resistor value decreases. For resistor value

selections, see Figure 2-1 or use Equation 4-1. The

switching frequency range is 65 kHz to 250 kHz, with

an accuracy of ±20%. In general, the lower the

switching frequency, the greater the input current is

drawn to deliver more power to the output. However,

the switching frequency should not be so low as to

allow the voltage at the switch node or the CS pin to go

beyond the absolute maximum voltage of those pins.

EQUATION 4-1:

4.4

EL Frequency

The EL lamp frequency is controlled via an external

resistor connected between the REL pin and VDD pin

of the device. The lamp frequency increases as the

resistor value decreases. For resistor value selections,

see Figure 2-2 or use Equation 4-2. The EL lamp

frequency range is 60 Hz to 1000 Hz, with an accuracy

of ±20%.

EQUATION 4-2:

FIGURE 4-2:

200 Hz Output Waveform.

VIN = 3.6V

IIN = 17mA

L = 220μH

COUT = 2.7nF

LAMP = 2 in2

RSW

REL

Time (2ms/div)

fSW kHz





RSW M





-------------------------

fEL Hz





360

REL M





------------------------

VIN = 3.6V

IIN = 27mA

L = 220μH

COUT = 2.7nF

LAMP = 2 in2

RSW

REL

Time (2ms/div)

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