MC34066 Datasheet, PDF (4/12 Pages) ON Semiconductor – High Performance High Performance

MC34066 MC33066
Figure 1. MC34066 Representative Block Diagram
VCC
15
Enable/
UVLO Adjust ₉
Osc Deadtime
ROSC
RDT ¹
Osc RC
2
COSC
One–Shot RC
16
CT
RT _{Osc Control}
Current
3
IOSC RVFO
Error Amp ⁶
Output
Error Amp 7
Inverting Input
Error Amp
Noninverting Input ⁸
CSoft–Start
11
50k
7k
7k
+
50k _–
8V ^{VCC UVLO}
VCC
Reference
Regulator
Q1
IOSC
Q2
5.1V
– ^Oscillator
+
4.9V/3.6V
One–Shot
–
+
4.9V/3.6V
5.1V
Vref UVLO
–
UVLO
+
4.2V/4V
Steering
Flip–Flop
Q
T
ton
Q
R
Current Mirror
+
Error Amp
–
Output Clamp
2.5V
EA Clamp
UVLO + Fault
R
Q
S
Fault
Latch
–
+
Error
Amplifier
Soft–Start
Buffer
9µA
5 ^Vref
Gnd
4
Drivers
Drive
14 ^{Output A}
Drive
12 ^{Output B}
Drive
13 ^Gnd
Fault
Comparator ₊
Fault
–
1.0V
Fault
10 Input
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 1 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.
Primary Control Path
The output pulse width and repetition rate are regulated
through the interaction of the variable frequency Oscillator,
One–Shot timer and Error Amplifier. The Oscillator triggers
the One–Shot which generates a pulse that is alternately
steered to a pair of totem–pole output drivers by a toggle
Flip–Flop. The Error Amplifier monitors the output of the
regulator and modulates the frequency of the Oscillator.
High–speed Schottky logic is used throughout the primary
control channel to minimize delays and enhance high
frequency characteristics.
4
MOTOROLA ANALOG IC DEVICE DATA