TEXAS INSTRUMENTS UC1853, UC2853, UC3853 Technical data

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High Power Factor Preregulator

UC1853 UC2853 UC3853

FEATURES

• Complete 8-pin Power Factor Solution

• Reduced External Components

• RMS Line Voltage Compensation

• Precision Multiplier/Squarer/Divider

• Internal 75kHz Synchronizable

Oscillator

• Average Current Mode PWM Control

• Overvoltage Protection Comparator

• High Current, Clamped Gate Driver

BLOCK DIAGRAM

DESCRIPTION

The UC3853 provides simple, yet high performance active power factor correction. Using the same control technique as the UC1854, this 8-pin device exploits a simplified architecture and an internal oscillator to minimize external component count. The UC3853 incorporates a precision multiplier/squarer/divider circuit, voltage and current loop error amplifiers, and a precision voltage reference to implement average current mode control with RMS line voltage compensation. This control technique maintains constant loop gain with changes in input voltage, which minimizes input line current distortion over the worldwide input voltage range.

The internal 75kHz oscillator includes an external clock input, allowing synchronization to downstream converters. Additionally, the device features an overvoltage protection comparator, a clamped MOSFET gate driver which self-biases low during undervoltage lockout, and low startup and supply current.

These devices are available in 8-pin plastic and ceramic dual in-line (DIP) packages, and 8-lead small outline (SOIC) packages. The UC1853 is specified for operation from –55°C to +125°C, the UC2853 is specified for operation from –25°C to +85°C, and the UC3853 is specified for operation from 0°C to +70°C.

11/97

UDG-94120-1

UC1853 UC2853 UC3853

ABSOLUTE MAXIMUM RATINGS

Supply Voltage (VCC) .............................40V

Output Drive Current,

Continuous ................................0.125A

Peak .......................................0.5A

Output Minimum Voltage.........................–0.3V

IAC Maximum Input Current........................1mA

IMO Maximum Output Current .....................–2mA

IMO Minimum Voltage ...........................–0.3V

FB Maximum Input Voltage ..........................5V

VCOMP Maximum Voltage.........................6.2V

ICOMP Sourcing Current ....................Self-Limiting

ICOMP Sinking Current ..........................20mA

ICOMP Maximum Voltage .........................7.2V

Storage Temperature ...................–65°C to +150°C

Junction Temperature...................–55°C to +150°C

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

CONNECTION DIAGRAM

DIL-8, SOIC-8 (Top View) JorN,DPackage

All voltages with respect to GND.Currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages.

ELECTRICAL CHARACTERISTICS

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

Undervoltage Lockout Section

VCC Turn-on Threshold V

Hysteresis 1.5 1.8 2.1 V

Supply Current Section

CC Startup VCC = 8V, IAC = 100µA; VVCOMP,VICOMP Open 250 500

IVCC IAC=0µA, VICOMP =0V 10 15 mA

Voltage Loop Error Amplifier Section

Transconductance IOUT=±20µA 0-70C 300 450 575 µmho

Input Voltage 0-70C 2.925 3 3.075 V

AVOL V

Output Sink Current V

Output Source Current VFB = 2.8V, VVCOMP = 3.75V –50 –20 µA

Output Voltage High 5.5 6 V

Output Voltage Low 0.6 0.9 V

Current Loop Error Amplifier Section

Offset Voltage 06mV

Voltage Gain V

Sink Current VIMO = 100mV, VICOMP =3V 1 mA

Source Current VIMO = –0.1V, VICOMP = 3V –150 –80

Output High I

Output Low IICOMP =50mA 0.3 0.8 V

PWM Modulator Gain VICOMP = 2V – 3V (Note 1) 20 %/V

Unless otherwise stated, these parameters apply for TA = –55°C to +125°C for the UC1853; –25°C to +85°C for the 2853; and 0°C to +70°C for the UC3853; VCC = 16V, VFB = 3V, IAC = 100mA, VVCOMP = 3.75V, VICOMP = 3V, TA =TJ.

VCOMP,VICOMP Open 11.5 13 V

Temperature 135 640 µmho

Temperature 2.9 3.1 V

VCOMP =1V–4V 50 60 dB FB = 3.2V, VVCOMP = 3.75V 20 50 µA

ICOMP =1V–4V 70 dB

ICOMP = –50mA 6 6.8 V

UC1853 UC2853 UC3853

ELECTRICAL CHARACTERISTICS

(continued)

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

Multiplier Section

Output Current – IAC Limited VCC = 11V, VVCOMP = 6V –230 –200 –170 µA

Output Current – Zero IAC = 0µA –2 –0.2 2 µA

Output Current – Power Limited VCC = 12V, V

Output Current VCC= 12V, V

Multiplier Gain Constant VCC= 12V, VVCOMP = 5.5V (Note 2) –1.05 –0.9 –0.75 V

Oscillator Section

Oscillator Initial Frequency TA = 25°C 67.5 75 82.5 kHz

Oscillator Frequency Line, Load, Temperature 56 75 94 kHz

Synchronization Frequency Range 100 kHz

Synchronization Pulse Amplitude Pulse slew rate = 100V/msec (Note 3) 2 V

Output Driver Section

Maximum Output Voltage 0mA load, VCC = 20V 12 15 17.5 V

Output High 0mA load, VCC = 12V, ref. to VCC –2.7 –1.7 V

Output Low (Device Inactive) Vcc = 0V, 20mA load (Sinking) 0.9 2.0 V

Output Low (Device Active) 50mA load (Sinking) 0.5 1 V

OUT Rise Time 1nF from OUT to GND 55 100 ns

OUT Fall Time 1nF from OUT to GND 35 100 ns

OUT Maximum Duty Cycle V

OVP Comparator Section

Threshold Voltage Volts Above EA Input V 90 150 mV

Hysteresis 80 mV

VCOMP = 5.5V –236 –178 –168 µA

VCOMP = 2V –22 µA

VCC= 12V, VVCOMP = 5V –156 µA VCC= 40V, VVCOMP =2V –2 µA VCC= 40V, V

–50mA load, VCC = 12V, ref. to VCC –3 –2.2 V

ICOMP =0V 88 93 %

VCOMP = 5V –14 µA

–1

Note 1:

DutyCycle

PWM modulator gain

∆

ICOMP

∆

Note 2:

Gain constant K

()

•

IMO VCC

••

VCC

, VCC = 12V.

IAC VCOMP V

(.)

Note 3. Synchronization is accomplished with a falling edge of 2V mag-

nitude and 100V/

sec slew rate.

PIN DESCRIPTIONS

FB: Voltage Amplifier Inverting Input, Overvoltage

Comparator Input, Sync Input. This pin serves three functions. FB accepts a fraction of the power factor corrected output voltage through a voltage divider, and is nominally regulated to 3V. FB voltages 5% greater than nominal will trip the overvoltage comparator, and shut down the output stage until the output voltage drops 5%. The internal oscillator can be synchronized through FB by injecting a 2V clock signal though a capacitor. To prevent false tripping of the overvoltage comparator, the clock signal must have a fast falling edge, but a slow rising edge.See Application Note U-159 for more information.

GND: Ground. All voltages are measured with respect to GND. The VCC bypass capacitor should be connected to ground as close to the GND pin as possible.

IAC: AC Waveform Input. This input provides voltage waveform information to the multiplier. The current loop will try to produce a current waveform with the same shape as the IAC signal. IAC is a low impedance input, nominally at 2V, which accepts a current proportional to the input voltage. Connect a resistor from the rectified input line to IAC which will conduct 500mA at maximum line voltage.

IMO: Multiplier Output and Current Sense Inverting Input. The output of the multiplier and the inverting input of the current amplifier are connected together at IMO. Avoid bringing this input below –0.5V to prevent the internal protection diode from conducting. The multiplier output is a current, making this a summing node and allowing a differential current error amplifier configuration to reject ground noise. The input resistance at this node should be

3.9k to minimize input bias current induced offset voltage. See the Applications section for the recommended circuit configuration.

OUT: Gate Driver Output.OUT provides high current gate drive for the external power MOSFET. A 15V clamp pre-

UC1853 UC2853 UC3853

vents excessive MOSFET gate-to-source voltage so that the UC3853 can be operated with VCC and high as 40V. A series gate resistor of at least 5 ohms should be used to minimize clamp voltage overshoot. In addition, a Schottky diode such as a 1N5818 connected between OUT and GND may be necessary to prevent parasitic substrate diode conduction.

ICOMP: Current Loop Error Amplifier Output. The current loop error amplifier is a conventional operational amplifier with a 150µA current source class A output stage. Compensate the current loop by placing an impedance between ICOMP and IMO. This output can swing above the oscillator peak voltage, allowing zero duty cycle when necessary.

VCC: Input Supply Voltage. This pin serves two functions. It supplies power to the chip, and an input voltage level signal to the squarer circuit. When this input is connected to a DC voltage proportional to the AC input RMS voltage, the voltage loop gain is reduced by

This configuration maintains constant loop gain. The UC3853 input voltage range extends from 12V to 40V, allowing an AC supply voltage range in excess of 85VAC to 265VAC. Bypass VCC with at least a 0.1µF ceramic capacitor to ensure proper operation. See the Applications section for the recommended circuit configuration.

VCOMP: Voltage Loop Error Amplifier Output. The voltage loop error amplifier is a transconductance type operational amplifier. A feedback impedance between VCOMP and FB for loop compensation must be avoided to maintain proper operation of the overvoltage protection comparator. Instead, compensate the voltage loop with an impedance between VCOMP and GND. When VCOMP is below 1.5V, the multiplier output current is zero.

UC3853 TYPICAL APPLICATION

UC1853 UC2853 UC3853

Note: the application circuit shownis a 100W, 75KHz design. Additional application information can be found in Application Note U–159 and Design Note DN–78.

UNITRODE CORPORATION 7 CONTINENTAL BLVD.• MERRIMACK, NH 03054 TEL. (603) 424-2410 • FAX (603) 424-3460

UDG-97127

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TEXAS INSTRUMENTS UC1853, UC2853, UC3853 Technical data

Specifications and Main Features

Frequently Asked Questions

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