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  • Contents

Description

UC3842 is a current control pulse width modulation chip with excellent performance. UC3842 modulator single-ended output can directly drive a bipolar power tube or field-effect tube.

uc3842bCatalog

UC3842B Documents and Media

UC3842B Advantages

UC3842B Features

UC3842B Simplified Block Diagram

UC3842B Pinout

UC3842B Package Information

UC3842B Block Diagram

UC3953B Timing Diagram

UC3953B Packages

UC3842B Circuit

Product Manufacturer

FAQ

Ordering & Quantity

UC3842B Documents and Media

PCN Assembly/Origin

PDIP-8 Assembly Revised 03/Sep/2013

Datasheets

UC384(2,3)B, UC284(2,3)B

HTML Datasheet

UC384(2,3)B, UC284(2,3)B

Environmental Information

Material Declaration UC3842BNG

EDA / CAD Models

Download from Ultra Librarian

Online Catalog

Multi-Topology


UC3842B Advantages

The UC3842B, UC3843B series are high performance fixed frequency current mode controllers. They are specifically designed for Off−Line and DC−DC converter applications offering the designer a cost−effective solution with minimal external components. These integrated circuits feature a trimmed oscillator for precise duty cycle control, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET.

Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle−by−cycle current limiting, programmable output deadtime, and a latch for single pulse metering.

These devices are available in an 8−pin dual−in−line and surface mount (SOIC−8) plastic package as well as the 14−pin plastic surface mount (SOIC−14). The SOIC−14 package has separate power and ground pins for the totem pole output stage.

The UCX842B has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off−line converters. The UCX843B is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).


UC3842B Features

  • Trimmed Oscillator for Precise Frequency Control
  • Oscillator Frequency Guaranteed at 250 kHz
  • Current Mode Operation to 500 kHz
  • Automatic Feed Forward Compensation
  • Latching PWM for Cycle−By−Cycle Current Limiting
  • Internally Trimmed Reference with Undervoltage Lockout
  • High Current Totem Pole Output
  • Undervoltage Lockout with Hysteresis
  • Low Startup and Operating Current
  • This is a Pb−Free and Halide−Free Device

UC3842B Simplified Block Diagram

uc3842b simplified block diagram


UC3842B Pinout

uc3842b pinout

8−Pin

14−Pin

Function

Description

1

1

Compensation

This pin is the Error Amplifier output and is made available for loop compensation.

2

3

Voltage Feedback

This is the inverting input of the Error Amplifier. It is normally connected to the switching power supply output through a resistor divider.

3

5

Current Sense

A voltage proportional to inductor current is connected to this input. The PWM uses this information to terminate the output switch conduction.

4

7

RT/CT

The Oscillator frequency and maximum Output duty cycle are programmed by connecting resistor RT to Vref and capacitor CT to ground. Operation to 500 kHz is possible.

5

 

GND

This pin is the combined control circuitry and power ground.

6

10

Output

This output directly drives the gate of a power MOSFET. Peak currents up to 1.0 A are sourced and sunk by this pin.

7

12

VCC

This pin is the positive supply of the control IC.

8

14

Vref

This is the reference output. It provides charging current for capacitor CT through resistor RT

 

8

Power Ground

This pin is a separate power ground return that is connected back to the power source. It is used to reduce the effects of switching transient noise on the control circuitry.

 

11

VC

The Output high state (VOH) is set by the voltage applied to this pin. With a separate power source connection, it can reduce the effects of switching transient noise on the control circuitry.

 

9

GND

This pin is the control circuitry ground return and is connected back to the power source ground.

 

2,4,6,13

NC

No connection. These pins are not internally connected.


UC3842B Package Information

Document Title

Document ID/Size

Revision

Revision Date

8 LEAD PDIP

626-05 (51kB)

P

Oct, 2019

SOIC-14 NB

751A-03 (49kB)

L

Oct, 2019

SOIC-8 Narrow Body

751-07 (53kB)

AK

Oct, 2019


UC3842B Block Diagram

uc3842b block diagram


UC3953B Timing Diagram

uc3953b timing diagram


UC3953B Packages

uc3953b packages

 


UC3842B Circuit

  • Oscillator Configuration

  • External Clock Synchronization

  • External Duty Cycle Clamp and Multi-Unit Synchronization

  • Adjustable Reduction of Clamp Level

  • Soft-Start Circuit

  • Adjustable Buffered Reduction of Clamp Level with Soft-Start

  • Current Sensing Power MOSFET

  • Current Waveform Spike Suppression

  • MOSFET Parasitic Oscillations

  • Bipolar Transistor Drive

  • Isolated MOSFET Drive

  • Latched Shutdown

  • Error Amplifier Compensation

  • Slop Compensation

  • 27 W Off-Line Flyback Regulator


Product Manufacturer

ON Semiconductor (Nasdaq: ON) is driving energy efficient innovations, empowering customers to reduce global energy use. The company offers a comprehensive portfolio of energy efficient power and signal management, logic, discrete and custom solutions to help design engineers solve their unique design challenges in automotive, communications, computing, consumer, industrial, LED lighting, medical, military/aerospace and power supply applications. ON Semiconductor operates a responsive, reliable, world-class supply chain and quality program, and a network of manufacturing facilities, sales offices and design centers in key markets throughout North America, Europe, and the Asia Pacific regions.


FAQ

What is UC3842?

The UC3842 is an integrated pulse width modulator (PWM) designed with both these objectives in mind. This IC provides designers an inexpensive control- ler with which they can obtain all the performance advantages of current-mode operation.

 

What is switching frequency range of UC3842?

The UC3842 oscillator runs AT the switching fre- quency. Each oscillator of the UC3842/3/4/5 family can be used to a maximum of 500 kHz.

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