Document
UC1842, UC2842, UC3842, UC1843, UC2843, UC3843 UC1844, UC2844, UC3844, UC1845, UC2845, UC3845
SLUS223G – APRIL 1997 – REVISED JULY 2022
UCx84x Current-Mode PWM Controllers
1 Features
• Optimized for off-line and DC-to-DC converters • Low start-up current (< 1 mA) • Automatic feedforward compensation • Pulse-by-pulse current limiting • Enhanced load-response characteristics • Undervoltage lockout with hysteresis • Double-pulse suppression • High-current totem-pole output • Internally trimmed bandgap reference • Up to 500-kHz operation • Error amplifier with low output resistance
2 Applications
• Switching regulators of any polarity • Transformer-coupled DC-DC converters
3 Description
The UCx84x series of control integrated circuits provide the features that are necessary to implement off-line or DC-to-DC fixed-frequency current-mode control schemes, with a minimum number of external components. The internally implemented circuits include an undervoltage lockout (UVLO), featuring a start-up current of less than 1 mA, and a precision reference trimmed for accuracy at the error amplifier input. Other internal circuits include logic to ensure latched operation, a pulse-width modulation (PWM) comparator that also provides current-limit control, and a totem-pole output stage that is designed to source or sink high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low when it is in the off state.
VIN
The UCx84x family offers a variety of package options, temperature range options, choice of maximum duty cycle, and choice of turnon and turnoff thresholds and hysteresis ranges. Devices with higher turnon or turnoff hysteresis are ideal choices for offline power supplies, while the devices with a narrower hysteresis range are suited for DC-DC applications. The UC184x devices are specified for operation from –55°C to 125°C, the UC284x series is specified for operation from –40°C to 85°C, and the UC384x series is specified for operation from 0°C to 70°C.
Device Information(1)
PART NUMBER
PACKAGE (PIN) BODY SIZE (NOM)
CDIP (8)
9.60 mm × 6.67 mm
UC184x
LCCC (20)
8.89 mm × 8.89 mm
CFP (8)
9.21 mm × 5.97 mm
SOIC (8)
4.90 mm × 3.91 mm
UC284x
SOIC (14) PDIP (8) SOIC (8)
8.65 mm × 3.91 mm 9.81 mm × 6.35 mm 4.90 mm × 3.91 mm
UC384x
SOIC (14) PDIP (8)
8.65 mm × 3.91 mm 9.81 mm × 6.35 mm
CFP (8)
9.21 mm × 5.97 mm
(1) For all available packages, see the orderable addendum at the end of the datasheet.
VCC
OUTPUT
VREF
ISENSE
UC2843 VFB
RT/CT GROUND COMP
Copyright © 2016, Texas Instruments Incorporated
Simplified Application
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.
UC1842, UC2842, UC3842, UC1843, UC2843, UC3843 UC1844, UC2844, UC3844, UC1845, UC2845, UC3845
SLUS223G – APRIL 1997 – REVISED JULY 2022
www.ti.com
Table of Contents
1 Features............................................................................1 2 Applications..................................................................... 1 3 Description.......................................................................1 4 Revision History.............................................................. 2 5 Device Comparison Table...............................................3 6 Pin Configuration and Functions...................................3 7 Specifications.................................................................. 6
7.1 Absolute Maximum Ratings........................................ 6 7.2 ESD Ratings............................................................... 6 7.3 Recommended Operating Conditions.........................6 7.4 Thermal Information....................................................6 7.5 Electrical Characteristics.............................................7 7.6 Typical Characteristics................................................ 9 8 Detailed Description...................................................... 11 8.1 Overview................................................................... 11 8.2 Functional Block Diagrams....................................... 11 8.3 Feature Description...................................................12
8.4 Device Functional Modes..........................................20 9 Application and Implementation.................................. 21
9.1 Application Information............................................. 21 9.2 Typical Application.................................................... 21 10 Power Supply Recommendations..............................34 11 Layout........................................................................... 35 11.1 Layout Guidelines................................................... 35 11.2 Layout Example...................................................... 36 12 Device and Documentation Supp.