Controller. UCC28742 Datasheet

UCC28742 Datasheet PDF

Part UCC28742
Description High-Efficiency Flyback Controller
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UCC28742
Product
Folder
Order
Now
Technical
Documents
Tools &
Software
Support &
Community
Reference
Design
UCC28742
SLUSD71A – APRIL 2018 – REVISED MAY 2018
UCC28742 High-Efficiency Flyback Controller with Optocoupler Feedback
1 Features
1 Opto-Coupled Feedback Enables up to 1%
Regulation
• Accurate Current Limit with Overload Timeout
Protection and Delayed Hiccup Response
• Resonant-Ring Valley-Switching Operation for
Highest Overall Efficiency
• 80-kHz Maximum Switching Frequency
• Frequency Dithering to Ease EMI Compliance
• Clamped Gate-Drive Output for MOSFET
• Ultra-Low Start-Up Current and Large VDD
Hysteresis
– High Value Start-Up Resistor
– Low Bias Capacitance
• Fault Protections
– Input Low Line
– Output Over-Voltage
– Over-Current
– Short-Circuit
• SOT23-6 Package
• Create a Custom Design Using the UCC28742
with the WEBENCH® Power Designer
2 Applications
• Industrial and Medical AC-to-DC Power Supplies
• Smart Electricity Meters
• Bias Supply for UPS, Server PSU, etc.
• Power Supply for Cable Modem, Television, Set-
Top Box, and Wireless Routers
• AC-to-DC Power Supply for Appliances
Simplified Schematic
VBULK
+ VF -
VOUT
CB1
CB2
NP NS
COUT
VAC
RSTR
VAUX
+ VFA -
NA
RS1
RS2
VVDD
CVDD
VDD
UCC28742
SOT23-6
VE
VS
DRV
CFB3
RFB3
CS
IFB
RFB4
FB
GND
RLC
RCS
RTL
IOPT
ROPT
RFB1
ZFB
RFB2
3 Description
The UCC28742 off-line flyback controller is a highly
integrated, 6-pin secondary-side regulated PWM
controller for efficient AC-to-DC power supplies. It is
an isolated-flyback power-supply controller that
provides Constant-Voltage (CV) using an optical
coupler to improve transient response to large-load
steps. This device processes information from opto-
coupled feedback and an auxiliary flyback winding for
high-performance control of output voltage and
current.
The UCC28742 employs advanced control algorithms
to achieve high operating efficiency and performance.
The drive output interfaces to a MOSFET power
switch. Discontinuous conduction mode (DCM) with
valley-switching reduces switching losses. Modulation
of switching frequency and primary current-peak
amplitude (FM and AM) keeps the conversion
efficiency high across the entire load and line ranges.
The controller has a maximum switching frequency of
80 kHz and always maintains control of the peak-
primary current in the transformer. A minimum
switching frequency of 200 Hz facilitates the
achievement of low no-load input power.
Device Information (1)
PART NUMBER PACKAGE
BODY SIZE (NOM)
UCC28742
SOT23-6
2.90 mm × 1.60 mm
(1) For all available packages, see the orderable addendum at
the end of the datasheet.
Typical Efficiency of a 10-W, 5-V AC-to-DC
Converter
85%
82.5%
80%
77.5%
75%
72.5%
70%
67.5%
65%
62.5%
60%
10%
20%
30%
40% 50% 60% 70%
Output Power
115 V RMS
230 V RMS
80% 90% 100%
D001
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.



UCC28742
UCC28742
SLUSD71A – APRIL 2018 – REVISED MAY 2018
www.ti.com
Table of Contents
1 Features .................................................................. 1
2 Applications ........................................................... 1
3 Description ............................................................. 1
4 Revision History..................................................... 2
5 Pin Configuration and Functions ......................... 3
6 Specifications......................................................... 4
6.1 Absolute Maximum Ratings ...................................... 4
6.2 ESD Ratings ............................................................ 4
6.3 Recommended Operating Conditions....................... 4
6.4 Thermal Information .................................................. 5
6.5 Electrical Characteristics........................................... 5
6.6 Typical Characteristics .............................................. 7
7 Detailed Description .............................................. 9
7.1 Overview ................................................................... 9
7.2 Functional Block Diagram ......................................... 9
7.3 Feature Description................................................. 10
7.4 Device Functional Modes........................................ 21
8 Applications and Implementation ...................... 22
8.1 Application Information............................................ 22
8.2 Typical Application .................................................. 22
8.3 Do's and Don'ts ....................................................... 31
9 Power Supply Recommendations...................... 32
10 Layout................................................................... 32
10.1 Layout Guidelines ................................................. 32
10.2 Layout Example .................................................... 33
11 Device and Documentation Support ................. 34
11.1 Device Support .................................................... 34
11.2 Documentation Support ....................................... 37
11.3 Receiving Notification of Documentation Updates 38
11.4 Community Resources.......................................... 38
11.5 Trademarks ........................................................... 38
11.6 Electrostatic Discharge Caution ............................ 38
11.7 Glossary ................................................................ 38
12 Mechanical, Packaging, and Orderable
Information ........................................................... 38
4 Revision History
DATE
May 2018
REVISION
A
NOTES
Initial release.
2 Submit Documentation Feedback
Product Folder Links: UCC28742
Copyright © 2018, Texas Instruments Incorporated



UCC28742
www.ti.com
5 Pin Configuration and Functions
SOT23-6 Package
6-Pin DBV
Top View
FB 1
6 VS
UCC28742
SLUSD71A – APRIL 2018 – REVISED MAY 2018
VDD 2
DRV 3
5 GND
4 CS
PIN
NAME
NO.
CS 4
DRV
3
FB 1
GND
VDD
5
2
VS 6
Pin Functions
I/O DESCRIPTION
The current-sense (CS) input connects to a ground-referenced current-sense resistor in series with the
I power switch. The resulting voltage monitors and controls the peak primary current. A series resistor is
added to this pin to compensate for peak switch current levels as the AC-mains input varies.
O DRV is an output pin used to drive the gate of an external high voltage MOSFET switching transistor.
The feedback (FB) input receives a current signal from the optocoupler output transistor. An internal
I
current mirror divides the feedback current applies it to an internal pullup resistor to generate a control
voltage, VCL. The voltage at this resistor directly drives the control law function, which determines the
switching frequency and the peak amplitude of the switching current.
The ground (GND) pin is both the reference pin for the controller, and the low-side return for the drive
G output. Special care must be taken to return all AC-decoupling capacitors as close as possible to this pin
and avoid any common trace length with analog signal-return paths.
P
VDD is the bias supply input pin to the device. A carefully placed bypass capacitor to GND is required on
this pin. Typical bypass capacitor values are from 0.047 µF to 10 µF depending on a design.
Voltage sense (VS) is an input used to provide demagnetization timing feedback to the controller to limit
frequency, to control constant-current operation, and to provide output-overvoltage detection. VS is also
I used for AC-mains input-voltage detection for peak primary-current compensation. This pin connects to a
voltage divider between an auxiliary winding and GND. The value of the upper resistor of this divider
programs the AC-mains run and stop thresholds, and factors into line compensation at the CS pin.
Copyright © 2018, Texas Instruments Incorporated
Product Folder Links: UCC28742
Submit Documentation Feedback
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