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UC2845D Datasheet Preview

UC2845D Datasheet

Current-Mode PWM Controller

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UC1842, UC2842, UC3842, UC1843, UC2843, UC3843

UC1844, UC2844, UC3844, UC1845, UC2845, UC3845

SLUS223F – APRIL 1997 – REVISED APRIL 2020

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.

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 off-line 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)

8.65 mm × 3.91 mm

PDIP (8)

9.81 mm × 6.35 mm

SOIC (8)

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.

Simplified Application

VIN

VCC

OUTPUT

VREF

ISENSE

UC2843

VFB

RT/CT

GROUND COMP

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.

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UC2845D Datasheet Preview

UC2845D Datasheet

Current-Mode PWM Controller

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UC1842, UC2842, UC3842, UC1843, UC2843, UC3843

UC1844, UC2844, UC3844, UC1845, UC2845, UC3845

SLUS223F – APRIL 1997 – REVISED APRIL 2020

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 ..................... 32

11 Layout................................................................... 33

11.1 Layout Guidelines ................................................. 33

11.2 Layout Example .................................................... 34

12 Device and Documentation Support ................. 35

12.1 Related Links ........................................................ 35

12.2 Receiving Notification of Documentation Updates 35

12.3 Community Resources.......................................... 35

12.4 Trademarks ........................................................... 35

12.5 Electrostatic Discharge Caution ............................ 35

12.6 Glossary ................................................................ 35

13 Mechanical, Packaging, and Orderable

Information ........................................................... 35

4 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision E (January 2017) to Revision F

Page

• Changed UVLO Table updated ............................................................................................................................................. 8

Changes from Revision D (August 2016) to Revision E

Page

• Changed VREFLECTED equation. ............................................................................................................................................. 23

• Changed DMAX equation. ..................................................................................................................................................... 24

Changes from Revision C (June 2007) to Revision D

Page

• Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation

section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and

Mechanical, Packaging, and Orderable Information section ................................................................................................. 1

• Changed values in the Thermal Information table ................................................................................................................ 6

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Current-Mode PWM Controller

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