UC1841

UC2841

UC3841

Programmable, Off-Line, PWM Controller

• All Control, Driving, Monitoring, and

Protection Functions Included

• Low-current, Off-line Start Circuit

• Voltage Feed Forward or Current

Mode Control

• Guaranteed Duty Cycle Clamp

• PWM Latch for Single Pulse per Period

• Pulse-by-Pulse Current Limiting Plus

Shutdown for Over-Current Fault

• No Start-up or Shutdown Transients

• Slow Turn-on Both Initially and After

Fault Shutdown

• Shutdown Upon Over- or

Under-Voltage Sensing

• Latch Off or Continuous Retry After

Fault

• PWM Output Switch Usable to 1A

Peak Current

• 1% Reference Accuracy

• 500kHz Operation

• 18 Pin DIL Package

The UC1841 family of PWM controllers has been designed to increase

the level of versatility while retaining all of the performance features of

the earlier UC1840 devices. While still optimized for highly-efficient boot-

strapped primary-side operation in forward or flyback power converters,

the UC1841 is equally adept in implementing both low and high voltage

input DC to DC converters. Important performance features include a

low-current starting circuit, linear feed-forward for constant volt-second

operation, and compatibility with either voltage or current mode topologies.

In addition to start-up and normal regulating PWM functions, these de-

vices include built in protection from over-voltage, under-voltage, and

over-current fault conditions with the option for either latch-off or automat-

ic restart.

While pin compatible with the UC1840 in all respects except that the po-

larity of the External Stop has been reversed, the UC1841 offers the fol-

lowing improvements:

1. Fault latch reset is accomplished with slow start discharge rather

than recycling the input voltage to the chip.

2. The External Stop input can be used for a fault delay to resist

shutdown from short duration transients.

3. The duty-cycle clamping function has been characterized and

specified.

The UC1841 is characterized for -55°C to +125°C operation while the

UC2841 and UC3841 are designed for -25°C to +85°C and 0°to +70°C,

respectively.

BLOCK DIAGRAM

Note: Positive true logic, latch outputs high with set, reset has priority.

6/93

DESCRIPTIONFEATURES

PARAMETER TEST CONDITIONS

UC1841 / UC2841 UC3841 UNITS

MIN TYP MAX MIN TYP MAX

Power Inputs

Start-Up Current V

IN = 30V, Pin 2 = 2.5V 4.5 6 4.5 6 mA

Operating Current V

IN = 30V, Pin 2 = 3.5V 10 14 10 14 mA

Supply OV Clamp I

IN = 20mA 33 40 45 33 40 45 V

Reference Section

Reference Voltage T

J = 25°C 4.95 5.0 5.05 4.9 5.0 5.1 V

Line Regulation V

IN = 8 to 30V 10 15 10 20 mV

Load Regulation I

L = 0 to 10mA 1020 1030mV

Temperature Stability Over Operating Temperature Range 4.9 5.1 4.85 5.15 V

Short Circuit Current V

REF = 0, TJ

= 25°C -80 -100 -80 -100 mA

Oscillator

Nominal Frequency T

= 25°C 47 50 53 45 50 55 kHz

Voltage Stability V

IN = 8 to 30V 0.5 1 0.5 1 %

Temperature Stability Over Operating Temperature Range 45 55 43 57 kHz

Maximum Frequency R

T = 2kΩ, CT = 330pF 500 500 kHz

UC1841

UC2841

UC3841

ELECTRICAL CHARACTERISTICS:

Unless otherwise stated, these specifications apply for TA = -55°C to +125°C for the

UC1841, -25°C to +85°C for the UC2841, and 0°C to +70°C for the UC3841; V

IN = 20V, RT = 20kΩ, CT = .001mfd, RR = 10kΩ,

R = .001mfd, Current Limit Threshold = 200mV, TA = TJ.

Supply Voltage, +V

(Pin 15) (Note 2)

Voltage Driven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +32V

Current Driven, 100mA maximum. . . . . . . . . . . . Self-limiting

PWM Output Voltage (Pin 12) . . . . . . . . . . . . . . . . . . . . . . . 40V

PWM Output Current, Steady-State (Pin 12) . . . . . . . . . 400mA

PWM Output Peak Energy Discharge . . . . . . . . . . . . 20µJoules

Driver Bias Current (Pin 14) . . . . . . . . . . . . . . . . . . . . . -200mA

Reference Output Current (Pin 16) . . . . . . . . . . . . . . . . -50mA

Slow-Start Sink Current (Pin 8) . . . . . . . . . . . . . . . . . . . . 20mA

IN Sense Current (Pin 11). . . . . . . . . . . . . . . . . . . . . . . . 10mA

Current Limit Inputs (Pins 6 & 7) . . . . . . . . . . . . . -0.5 to +5.5V

Stop Input (Pin 4) . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +5.5V

Comparator Inputs

(Pins 1, 7, 9-11, 16). . . . . . . . . . . . Internally clamped at 12V

Power Dissipation at T

A = 25°C (Note 3) . . . . . . . . . . . 1000mW

Power Dissipation at T

C = 25°C (Note 3). . . . . . . . . . . 2000mW

Operating Junction Temperature . . . . . . . . . . -55°C to +150°C

Storage Temperature Range. . . . . . . . . . . . . . -65°C to +150°C

Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . +300°C

Note 1: All voltages are with respect to ground, Pin 13.

Currents are positive-into, negative-out of the specified

terminal.

Note 2: All pin numbers are referenced to DIL-18 package.

Note 3: Consult Packaging Section of Databook for thermal

limitations and considerations of package.

CONNECTION DIAGRAMS

PLCC-20, LCC-20

(TOP VIEW)

Q or L Package

DIL-18, SOIC-18 (TOP VIEW)

J or N, DW Package

PACKAGE PIN FUNCTIONS

FUNCTION PIN

Comp 1

Start/UV 2

OV Sense 3

Stop 4

Reset 5

CUR Thresh 7

CUR Sense 8

Slow Start 9

T/CT 10

Ramp 11

IN Sense 12

PWM Out 13

Ground 14

Drive Bias 15

IN Supply 17

5.0V REF 18

Inv. Input 19

N.I. Input 20

ABSOLUTE MAXIMUM RATINGS

PARAMETER TEST CONDITIONS UC1841 / UC2841 UC3841 UNITS

MIN TYP MAX MIN TYP MAX

Ramp Generator

Ramp Current, Minimum I

SENSE = -10µA -11 -14 -11 -14 µA

Ramp Current, Maximum I

SENSE = 1.0mA -0.9 -.95 -0.9 -.95 mA

Ramp Valley 0.3 0.4 0.6 0.3 0.4 0.6 V

Ramp Peak Clamping Level 3.9 4.2 4.5 3.9 4.2 4.5 V

Error Amplifier

Input Offset Voltage V

CM = 5.0V 0.5 5 2 10 mV

Input Bias Current 0.5 2 1 5 µA

Input Offset Current 0.5 0.5 µA

Open Loop Gain ∆V

O= 1 to 3V 60 66 60 66 dB

Output Swing (Max. Output ≤

Ramp Peak - 100mV)

Minimum Total Range 0.3 3.5 0.3 3.5 V

CMRR V

CM = 1.5 to 5.5V 70 80 70 80 dB

PSRR V

IN = 8 to 30V 70 80 70 80 dB

Short Circuit Current V

COMP = 0V -4 -10 -4 -10 mA

Gain Bandwidth* T

J = 25°C, AVOL = 0dB 1 2 1 2 MHz

Slew Rate* T

J = 25°C, AVCL

= 0dB 0.8 0.8 V/µs

PWM Section

Continuous Duty Cycle

Range* (other than zero)

Minimum Total Continuous Range,

Ramp Peak < 4.2V

495495%

50% Duty Cycle Clamp R

SENSE to VREF = 10k 42 47 52 42 47 52 %

Output Saturation I

OUT = 20mA 0.2 0.4 0.2 0.4 V

OUT = 200mA 1.7 2.2 1.7 2.2 V

Output Leakage V

OUT = 40V 0.1 10 0.1 10 µA

Comparator Delay* Pin 8 to Pin 12, T

J = 25°C, RL = 1kΩ 300 500 300 500 ns

Sequencing Functions

Comparator Thresholds Pins 2, 3, 5 2.8 3.0 3.2 2.8 3.0 3.2 V

Input Bias Current Pins 3, 5 = 0V -1.0 -4.0 -1.0 -4.0 µA

Input Leakage Pins 3, 5 = 10V 0.1 2.0 0.1 2.0 µA

Start/UV Hysteresis Current Pin 2 = 2.5V 170 200 220 170 200 230 µA

Ext. Stop Threshold Pin 4 0.8 1.6 2.4 0.8 1.6 2.4 V

Error Latch Activate Current Pin 4 = 0V, Pin 3 > 3V -120 -200 -120 -200 µA

Driver Bias Saturation Voltage,

IN - VOH

IB = -50mA 2 3 2 3 V

Driver Bias Leakage V

B = 0V -0.1 -10 -0.1 -10 µA

Slow-Start Saturation I

S = 10mA 0.2 0.5 0.2 0.5 V

Slow-Start Leakage V

S = 4.5V 0.1 2.0 0.1 2.0 µA

Current Control

Current Limit Offset 0 5 0 10 mV

Current Shutdown Offset 370 400 430 360 400 440 mV

Input Bias Current Pin 7 = 0V -2 -5 -2 -5 µA

Common Mode Range* -0.4 3.0 -0.4 3.0 V

Current Limit Delay* T

J = 25°C, Pin 7 to 12, RL = 1k 200 400 200 400 ns

* These parameters are guaranteed by design but not 100% tested in production.

UC1841

UC2841

UC3841

ELECTRICAL CHARACTERISTICS:

Unless otherwise stated, these specifications apply for TA = -55°C to +125°C for the

UC1841, -25°C to +85°C for the UC2841, and 0°C to +70°C for the UC3841; V

IN = 20V, RT = 20kΩ, CT = .001mfd, RR = 10kΩ,

R = .001mfd, Current Limit Threshold = 200mV, TA = TJ.

Part #	UC2841DW
Description	PROG OFF-LINE PWM CONT - Rail/Tube
Category	IC
Availability	Out of Stock
Qty	0

UC2841DW

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Technical Document