UC1842/3/4/5 - CURRENT MODE PWM CONTROLLER - Features and Absolute Maximum Ratings

Q: What key features does the UC1842/3/4/5 current mode PWM controller provide?

It supports off-line and DC-to-DC fixed-frequency current-mode control, includes low startup current under-voltage lockout, automatic feed-forward compensation, pulse-by-pulse current limiting, and a totem-pole output stage for driving N-channel MOSFETs.

Q: How do the UC1842/UC1843 versus UC1844/UC1845 differ in duty-cycle capability?

UC1842 and UC1843 can approach duty cycles near 100%, while UC1844 and UC1845 achieve a 0% to 50% range by blanking the output every other clock cycle using an internal toggle flip-flop.

Q: What kind of limits are listed in the Absolute Maximum Ratings section?

It includes maximum supply voltage, output current and capacitive load output energy, allowed analog input voltage range, current limits for the error amp output sink, power dissipation limits by package and temperature, and storage/junction/lead temperature ranges.

Oct 12, 2026

Upload by hdkawk

UC1842/3/4/5 is a family of control devices for fixed-frequency current-mode PWM in off-line or DC-to-DC converters, designed with a minimal external parts count. It integrates under-voltage lockout with startup current below 1 mA, a trimmed bandgap reference feeding the error amplifier, PWM comparator-based current limiting, and a totem-pole output stage capable of sourcing or sinking high peak current for N-channel MOSFET drive. Differences among UC1842/3/4/5 define UVLO thresholds and maximum duty-cycle ranges, supported by multiple package options. The document also specifies absolute maximum ratings including supply, analog input limits, output current and energy for capacitive loads, temperature ranges, and thermal characteristics.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages23

Reading Time58 min

AccessFree to download

Features

Description

Block Diagram

Connection Diagrams

Absolute Maximum Ratings

Thermal Characteristics

Dissipation Ratings

Electrical Characteristics

CURRENT MODE PWM CONTROLLER FEATURES • Optimized For Off-line and DC-to-DC Converters • Low Start-Up Current (<1 mA) • Automatic Feed Forward Compensation • Pulse-by-Pulse Current Limiting • Enhanced Load Response Characteristics • Under-Voltage Lockout With Hysteresis • Double Pulse Suppression • High Current Totem Pole Output • Internally Trimmed Bandgap Reference • 500-kHz Operation • Low RO Error Amp DESCRIPTION The UC1842/3/4/5 family of control devices provides the necessary features to implement off-line or dc-to-dc fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include under-voltage lockout featuring start up current less than 1 mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM comparator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in the off state. Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC1842 and UC1844 have UVLO thresholds of 16 VON and 10 VOFF, ideally suited to off-line applications. The corresponding thresholds for the UC1843 and UC1845 are 8.4 V and 7.6 V. The UC1842 and UC1843 can operate to duty cycles approaching 100% . A range of zero to 50% is obtained by the UC1844 and UC1845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle. BLOCK DIAGRAM Vcc GROUND RT/CT VFB COMP CURRENT SENSE Note 1: A/B Note 2: A = DIL−8 Pin Number. B = SO−14 and CFP−14 Pin Number. Toggle flip flop used only in 1844 and 1845. Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. PRODUCTION DATA information is current as of publication date. Copyright © 1997–2007, Texas Instruments Incorporated Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 SLUS223C–APRIL 1997–REVISED JUNE 2007 [www.ti.com](www.ti.com) ABSOLUTE MAXIMUM RATINGS (1) | | | UNIT | | --- | --- | --- | | Supply voltage | Low impedance source | 30 V | | | ICC < 30 mA | Self Limiting | | Output current | | ±1 A | | Output energy (capacitive load) | | 5 µJ | | Analog inputs (Pins 2, 3) | | –0.3 V to 6.3 V | | Error amp output sink current | | 10 mA | | Power dissipation | TA≤ 25°C (DIL-8) | 1 W | | | TA≤ 25°C (SOIC-14) | 725 mW | | | TA≤ 25°C (SOIC-8) | 650 mW | | Storage temperature range | | –65°C to 150°C | | Junction temperature range | | –55°C to 150°C | | Lead temperature (soldering, 10 seconds) | | 300°C | (1) All voltages are with respect to Pin 5. All currents are positive into the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages. CONNECTION DIAGRAMS DIL-8, SOIC-8 N or J PACKAGE, D8 PACKAGE (TOP VIEW) COMP VFBI SENSE RT/CT | 1
2
3
4 | | 8
7
6 5
| | --- | --- | --- | V REF V CC OUTPUT GROUND SOIC-14, CFP-14 D or W PACKAGE (TOP VIEW) COMP NC VFB NCI SENSE NC RT/CT | | 1 | 14 | | | --- | --- | --- | --- | | | | | | | | | | | | | 2 | 13 | | | | | | | | | | | | | | 3 | 12 | | | | | | | | | | | | | | 4 | 11 | | | | | | | | | | | | | | 5 | 10 | | | | | | | | | | | | | | 6 | 9 | | | | | | | | | 7 | 8 | | | | | | | | | | | | V REF NC V CC VC OUTPUT GROUND PWR GND NC − No internal connection NC VFB NCI SENSE NC PLCC-20 Q PACKAGE (TOP VIEW) NC COMP NC VREF NC NC RT / CT NC

FAQs

What key features does the UC1842/3/4/5 current mode PWM controller provide?

It supports off-line and DC-to-DC fixed-frequency current-mode control, includes low startup current under-voltage lockout, automatic feed-forward compensation, pulse-by-pulse current limiting, and a totem-pole output stage for driving N-channel MOSFETs.

How do the UC1842/UC1843 versus UC1844/UC1845 differ in duty-cycle capability?

UC1842 and UC1843 can approach duty cycles near 100%, while UC1844 and UC1845 achieve a 0% to 50% range by blanking the output every other clock cycle using an internal toggle flip-flop.

What kind of limits are listed in the Absolute Maximum Ratings section?

It includes maximum supply voltage, output current and capacitive load output energy, allowed analog input voltage range, current limits for the error amp output sink, power dissipation limits by package and temperature, and storage/junction/lead temperature ranges.

Oct 12, 2026

Upload by hdkawk