MC34066, MC33066

http://onsemi.com

4

15

9

Enable/

UVLO Adjust

Osc Deadtime

1

Osc RC

2

One−Shot RC

16

Current

3

Error Amp

Output

Error Amp

Inverting Input

6

7

Error Amp

Noninverting Input 8

11

7k

50k

7k

50k

Reference

Regulator

5.1V

8V

UVLO

4.2V/4V

Q1

Q2

Drivers

5.1V

Oscillator

Steering

Flip−Flop

4.9V/3.6V

T

Q

Q

R

One−Shot

4.9V/3.6V

UVLO + Fault

Fault

Comparator

Q

R

S

Current Mirror

Error Amp

Output Clamp

Fault

Fault

Latch

1.0V

2.5V

EA Clamp

Soft−Start

Buffer

9

μA

Error

Amplifier

5

Gnd

4

14

12

13

10

Drive

Output B

Drive

Gnd

Fault

Input

−

+

+

−

+

−

−

+

−

+

+

−

+

−

Drive

Output A

Figure 2. MC34066 Representative Block Diagram

OPERATING DESCRIPTION

Introduction

As power supply designers have strived to increase power

conversion efficiency and reduce passive component size, high

frequency resonant mode power converters have emerged as

attractive alternatives to conventional square−wave control.

When compared to square−wave converters, resonant mode

control offers several benefits including lower switching

losses, higher efficiency, lower EMI emission, and smaller

size. This integrated circuit has been developed to support new

trends in power supply design. The MC34066 Resonant Mode

Controller is a high performance bipolar IC dedicated to

variable frequency power control at frequencies exceeding

1.0 MHz. This integrated circuit provides the features,

performance and flexibility for a wide variety of resonant

mode power supply applications.

The primary purpose of the control chip is to supply

precise pulses to the gates of external power MOSFETs at a

repetition rate regulated by a feedback control loop. The

MC34066 can be operated in any of three modes as follows:

1) fixed on−time, variable frequency; 2) fixed off−time,

variable frequency; and 3) combinations of 1 and 2 that

change from fixed on−time to fixed off−time as the

frequency increases. Additional features of the IC ensure

that system startup and fault conditions are administered in

a safe, controlled manner.

A simplified block diagram of the IC is shown on the first

page of this data sheet, which identifies the main functional

blocks and the block−to−block interconnects. Figure 2 is a

detailed functional diagram which accurately represents the

internal circuitry. The various functions can be divided into

two sections. The first section includes the primary control

path which produces precise output pulses at the desired

frequency Oscillator, a One−Shot, a pulse Steering

Flip−Flop, a pair of power MOSFET Drivers, and a wide

bandwidth Error Amplifier. The second section provides

several peripheral support functions including a voltage

reference, undervoltage lockout, Soft−Start circuit, and a

fault detector.