Datasheet

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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

Summary of content (11 pages)

PAGE 1
UC1841 UC2841 UC3841 Programmable, Off-Line, PWM Controller FEATURES DESCRIPTION • 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 • 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.
PAGE 2
UC1841 UC2841 UC3841 ABSOLUTE MAXIMUM RATINGS Supply Voltage, +VIN (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) . . . . . . . . . . . . . . . .
PAGE 3
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; VIN = 20V, RT = 20kΩ, CT = .001mfd, RR = 10kΩ, CR = .001mfd, Current Limit Threshold = 200mV, TA = TJ. PARAMETER TEST CONDITIONS UC1841 / UC2841 MIN TYP MAX -11 -14 -0.9 -.95 0.3 0.4 3.9 4.2 0.5 UC3841 UNITS MIN TYP MAX -11 -14 -0.9 -.95 0.6 0.3 0.4 0.6 V 4.5 3.9 4.2 4.
PAGE 4
UC1841 UC2841 UC3841 FUNCTIONAL DESCRIPTION PWM CONTROL 1. Oscillator Generates a fixed-frequency internal clock from an external RT and CT. Frequency = KC RTCT where KC is a first order correction factor ≈ 0.3 log (CT X 1012). 2. Ramp Generator Develops a linear ramp with a slope defined externally by 3. Error Amplifier 4. Reference Generator 5. PWM Comparator 6. PWM Latch 7. PWM Output Switch SEQUENCING FUNCTIONS 1. Start/UV Sense 2. Drive Switch 3. Driver Bias 4.
PAGE 5
UC1841 UC2841 UC3841 Start/UV Hysteresis PWM Output-Saturation Voltage Oscillator Frequency PWM Output Minimum Pulse Width Error Amplifier Open Loop Gain and Phase Shutdown Timing 5
PAGE 6
UC1841 UC2841 UC3841 OPEN-LOOP TEST CIRCUIT Nominal Frequency = 1 = 50 kHz RTCT  R1 + R2 + R3  Start Voltage = 3   +0.
PAGE 7
UC1841 UC2841 UC3841 Figure A. UC1841 Programmable PWM Controller In A Simplified Flyback Regulator Figure B.
PAGE 8
UC1841 UC2841 UC3841 PROGRAMMABLE SOFT START AND RESTART DELAY CIRCUIT ERROR LATCH INTERNAL CIRCUITRY The Error Latch consists of Q5 and Q6 which, when both on, turns off the PWM Output and pulls the Slow-Start pin low. This latch is set by either the Over-Voltage or Current Shutdown comparators, or by a high signal on Pin 4. Reset is accomplished by either the Reset comparator or a low signal on Pin 4.
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PACKAGE OPTION ADDENDUM www.ti.
PAGE 10
PACKAGE OPTION ADDENDUM www.ti.com 31-Oct-2013 (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device.
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IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.