UC1853 UC2853 UC3853 High Power Factor Preregulator PRELIMINARY FEATURES DESCRIPTION • Complete 8-pin Power Factor Solution • Reduced External Components • RMS Line Voltage Compensation • Precision Multiplier/Squarer/Divider 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. • Internal 75kHz Synchronizable Oscillator • Average Current Mode PWM Control • Overvoltage Protection Comparator • High Current, Clamped Gate Driver 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 −40°C to +85°C, and the UC3853 is specified for operation from 0°C to +70°C. BLOCK DIAGRAM UDG-94120-1 2/96 UC1853 UC2853 UC3853 ABSOLUTE MAXIMUM RATINGS CONNECTION DIAGRAM Supply Voltage (VDD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40V Output Drive Current, Continuous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.125A Peak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.5A IAC Maximum Input Current . . . . . . . . . . . . . . . . . . . . . . . .1mA IMO Maximum Output Current . . . . . . . . . . . . . . . . . . . . .–2mA FB Maximum Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . .5V VCOMP Maximum Voltage . . . . . . . . . . . . . . . . . . . . . . . . .6.2V ICOMP Sourcing Current . . . . . . . . . . . . . . . . . . . .Self-Limiting ICOMP Sinking Current . . . . . . . . . . . . . . . . . . . . . . . . . .20mA Storage Temperature . . . . . . . . . . . . . . . . . . .–65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . .–55°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . .+300°C 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. DIL-8, SOIC-8 (Top View) J or N, D Packages ELECTRICAL CHARACTERISTICS 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 = 100µA, VVCOMP = 3.75V, VICOMP = 3V, TA = TJ. PARAMETER Undervoltage Lockout Section VIN Turn-on Threshold VIN Turn-off Threshold Supply Current Section IIN Startup IIN Voltage Loop Error Amplifier Section Transconductance Input Voltage AVOL Output Sink Current Output Source Current Output Voltage High Output Voltage Low Current Loop Error Amplifier Section Offset Voltage GBW Voltage Gain Sink Current Source Current Output High Output Low PWM Modulator Gain Multiplier Section Output Current – IAC Limited Output Current – Zero Output Current – Power Limited Output Current Multiplier Gain Constant TEST CONDITIONS MIN TYP VVCOMP, VICOMP Open 11.5 9.5 VCC = 8V, IAC = 100µA; VVCOMP, VICOMP Open IAC = 0µA, VICOMP = 0V 250 10 VVCOMP = 1V - 4V VFB = 3.2V, VVCOMP = 3.75V VFB = 2.8V, VVCOMP = 3.75V 485 3 60 50 −50 6 0.6 0 FIN = 100kHz, 20mV p-p VICOMP = 1V - 4V VIMO = 100mV, VICOMP = 3V VIMO = −0.1V, VICOMP = 3V IICOMP = −50µA IICOMP = 50µA VICOMP = 2V - 3V (Note 1) VCC = 11V, VVCOMP = 6V IAC = 0µA VCC = 12V, VVCOMP = 5.5V VCC = 12V, VVCOMP = 2V VCC = 12V, VVCOMP = 5V VCC = 40V, VVCOMP = 2V VCC = 40V, VVCOMP = 5V VCC = 12V, VVCOMP = 5.5V (Note 2) 2 MAX UNITS V V 500 µmho V dB µA µA V V 6 mV MHz dB mA µA V V %/V −170 2 −168 µA µA µA µA µA µA µA V−2 1 70 1 −150 6.8 0.3 20 −230 −2 −236 −1.05 −200 −0.2 −178 −22 −156 −2 −14 −0.9 µA mA −0.75 UC1853 UC2853 UC3853 ELECTRICAL CHARACTERISTICS (cont.) 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 = 100µA, VVCOMP = 3.75V, VICOMP = 3V, TA = TJ. PARAMETER Oscillator Section Oscillator Initial Frequency Oscillator Frequency Synchronization Frequency Range Synchronization Pulse Amplitude Output Driver Section Maximum Output Voltage Output High Output Low (Device Inactive) Output Low (Device Active) OUT Rise Time OUT Fall Time OUT Maximum Duty Cycle OVP Comparator Section Threshold Voltage Hysteresis Note 1: PWM modulator gain = Note 2: Gain constant (K) = TEST CONDITIONS TA = 25°C Line, Load, Temperature MIN TYP 67.5 56 75 75 Pulse slew rate = 100V/µsec (Note 3) 0mA load, VCC = 20V 3 0mA load, VCC = 12V, ref. to VCC −50mA load, VCC = 12V, ref. to VCC VCC = 0V, 20mA load (Sinking) 50mA load (Sinking) 1nF from OUT to GND 1nF from OUT to GND VICOMP = 0V MAX UNITS 82.5 94 100 kHz kHz kHz V 15 -1.7 −2.2 0.9 0.5 55 35 93 17.5 V V V V V ns ns % 3.15 80 3.3 2 13 -2.5 −3 3.06 2.0 1 V mV ∆Duty Cycle ∆VICOMP · (VCOMP − 1.5V) , VCC = 12V. IMO ·VCC · VCC . 64 IAC Note 3: Synchronization is accomplished with a falling edge of 2V magnitude and 100V/µsec 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 the Applications section for recommended synchronization circuits. input line to IAC which will conduct 500µA 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. 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. OUT: Gate Driver Output. OUT provides high current gate drive for the external power MOSFET. A 15V clamp prevents 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. 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 3 UC1853 UC2853 UC3853 PIN DESCRIPTIONS (cont.) 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. 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. 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 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. 64 VCC2. UC3853 TYPICAL APPLICATION UDG-94121-2 UNITRODE INTEGRATED CIRCUITS 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 • FAX (603) 424-3460 4