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

SGLS318 − NOVEMBER 2005

  



www.ti.com

FEATURES

Controlled Baseline

− One Assembly/Test Site, One

Fabrication Site

D Extended Temperature Performance of −55°C

to 125°C

D Enhanced Diminishing Manufacturing

Sources (DMS) Support

D Enhanced Product-Change Notification

D Qualification Pedigree

†

D Controls Boost PWM to Near-Unity Power

Factor

D Limits Line Current Distortion To < 3%

D World-Wide Operation Without Switches

D Accurate Power Limiting

D Fixed-Frequency Average Current-Mode

Control

D High Bandwidth (5 MHz), Low-Offset Current

Amplifier

D Integrated Current- and Voltage Amplifier

Output Clamps

D Multiplier Improvements: Linearity, 500 mV

Offset (Eliminates External Resistor), 0 V

to 5 V Multout Common-Mode Range

D V

REF

GOOD Comparator

D Faster and Improved Accuracy ENABLE

Comparator

D UVLO Options (16 V/10 V or 10.5 V/10 V)

D 300-µA Start-Up Supply Current

†

Component qualification in accordance with JEDEC and industry standards to ensure reliable operation over an extended temperature range.

This includes, but is not limited to, Highly Accelerated Stress Test (HAST) or biased 85/85, temperature cycle, autoclave or unbiased HAST,

electromigration, bond intermetallic life, and mold compound life. Such qualification testing should not be viewed as justifying use of this

component beyond specified performance and environmental limits.

DESCRIPTION

The UC2854B products are pin compatible enhanced versions of the UC2854. Like the UC2854, these products

provide all of the functions necessary for active power factor corrected preregulators. The controller achieves

near unity power factor by shaping the ac-input line current waveform to correspond to the ac-input line voltage.

To do this the UC2854B uses average current mode control. Average current mode control maintains stable,

low distortion sinusoidal line current without the need for slope compensation, unlike peak current mode control.

A 1% 7.5-V reference, fixed frequency oscillator, PWM, voltage amplifier with soft-start, line voltage feedforward

RMS

squarer), input supply voltage clamp, and over current comparator round out the list of features.

The UC2854B is available in a DW (SOIC-Wide) package.

The UC2854A/B products improve upon the UC2854 by offering a wide bandwidth, low offset current amplifier,

a faster responding and improved accuracy enable comparator, a VREF GOOD comparator, UVLO threshold

options (16 V/10 V for offline, 10.5 V/10 V for startup from an auxiliary 12-V regulator), lower startup supply

current, and an enhanced multiply/divide circuit. New features like the amplifier output clamps, improved

amplifier current sinking capability, and low offset VAC pin reduce the external component count while improving

performance. Improved common mode input range of the multiplier output/current amplifier input allow the

designer greater flexibility in choosing a method for current sensing. Unlike its predecessor, R

SET

controls only

oscillator charging current and has no effect on clamping the maximum multiplier output current. This current

is now clamped to a maximum of 2 × I

at all times which simplifies the design process and provides foldback

power limiting during brownout and extreme low line conditions.

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Summary of content (13 pages)

PAGE 1
SGLS318 − NOVEMBER 2005 D Fixed-Frequency Average Current-Mode FEATURES D Controlled Baseline D D D D D D D D Control − One Assembly/Test Site, One Fabrication Site Extended Temperature Performance of −55°C to 125°C Enhanced Diminishing Manufacturing Sources (DMS) Support Enhanced Product-Change Notification Qualification Pedigree† Controls Boost PWM to Near-Unity Power Factor Limits Line Current Distortion To < 3% World-Wide Operation Without Switches Accurat
PAGE 2
SGLS318 − NOVEMBER 2005 BLOCK DIAGRAM VAO MOUT 7 5 CAO PKLMT 3 REF 2 9 VCC 7.5 V REF (A) 16 V / 10 V (B) 10.5 V / 10 V RUN ENA 10 3V 15 VCC A VSENSE 11 IAC 6 VRMS R R S Q B X2 8 7.1 V IC POWER 2.65 V / 2.15 V 14 µA SS 13 16 GTDRV C RUN I MOUT +A B 20 V OSC C 4 ISENSE 14 12 CT RSET 1 GND UDG−03110 These devices have limited built-in ESD protection.
PAGE 3
SGLS318 − NOVEMBER 2005 PACKAGE DESCRIPTION DW PACKAGE (TOP VIEW) GND PKLMT CAO ISENSE MOUT IAC VAO VRMS 1 16 2 15 3 14 4 13 5 12 6 11 7 10 8 9 GTDRV VCC CT SS RSET VSENSE ENA VREF ORDERING INFORMATION UVLO TURN-ON (V) TA PART NUMBERS UVLO TURN-OFF (V) SOIC−16 (DW) −55°C to 125°C 10.5 10 UC2854BMDWREP (1) The DW package is available taped and reeled. Add TR suffix to device type to order quantities of 2,000 devices per reel for the DW package.
PAGE 4
SGLS318 − NOVEMBER 2005 ELECTRICAL CHARACTERISTICS VCC = 18 V, RT = 8.2 kΩ, CT = 1.5 nF, VPKLMT = 1 V, VVRMS = 1.5 V, IIAC = 100 µA, IISENSE = 0 V, VCAO = 3.5 V, VVAO = 5 V, VVSENSE = 3 V TEST CONDITIONS PARAMETER MIN TYP MAX UNIT 250 400 µA mA OVERALL CAO = 0 V, VAO = 0 V, VCC = VUVLO−0.
PAGE 5
SGLS318 − NOVEMBER 2005 ELECTRICAL CHARACTERISTICS VCC = 18 V, RT = 8.2 kΩ, CT = 1.5 nF, VPKLMT = 1 V, VVRMS = 1.5 V, IIAC = 100 µA, IISENSE = 0 V, VCAO = 3.5 V, VVAO = 5 V, VVSENSE = 3 V TEST CONDITIONS PARAMETER MIN TYP MAX UNIT 100 115 kHz kHz OSCILLATOR Initial accuracy TA = 25°C 12 V ≤ VCC ≤ 18 V 85 Voltage stability Total variation Line, temperature 80 120 Ramp amplitude (peak-to-peak) 4.9 5.9 Ramp valley voltage 0.8 1.
PAGE 6
SGLS318 − NOVEMBER 2005 TERMINAL FUNCTIONS TERMINAL PACKAGES I/O DESCRIPTION 4 O Output of the wide bandwidth current amplifier and one of the inputs to the PWM duty-cycle comparator. The output signal generated by this amplifier commands the PWM to force the correct input current. The output can swing from 0.1 V to 7.5 V. 14 18 I Capacitor from CT to GND sets the PWM oscillator frequency ENA 10 13 I A nominal voltage above 2.65 V on this pin allows the device to begin operating.
PAGE 7
SGLS318 − NOVEMBER 2005 FUNCTIONAL DESCRIPTION The UC2854B is designed as a pin compatible upgrade to the industry standard UC2854 active power factor correction circuits. The circuit enhancements allow the user to eliminate in most cases several external components currently required to successfully apply the UC2854. In addition, linearity improvements to the multiply, square and divide circuitry optimizes overall system performance.
PAGE 8
SGLS318 − NOVEMBER 2005 Current Amplifier The current amplifier for an average current PFC controller needs a low offset voltage in order to minimize AC line current distortion. With this in mind, the UC2854B current amplifier has improved the input offset voltage from ±4 mV to 0 V to ±3 mV. The negative offset of the UC2854B assures that the PWM circuit will not drive the MOSFET is the current command is zero (both current amplifier inputs zero.
PAGE 9
SGLS318 − NOVEMBER 2005 TYPICAL CHARACTERISTICS GATE DRIVE TIMING vs LOAD CAPACITANCE 800 GATE DRIVE MAXIMUM DUTY CYCLE vs OSCILLATOR CHARGING RESISTANCE 100 700 95 Fall Time Duty Cycle − % t− Time − ns 600 500 400 Rise Time 300 90 85 80 200 75 100 0 0 0.01 0.02 0.03 0.04 70 1000 0.05 CLOAD − Load Capacitance − µF 10 k 100 k RSET − Oscillator Charging Resistance − Ω Figure 2 Figure 3 MULTIPLIER GAIN CONSTANT vs SUPPLY CURRENT 1.
PAGE 10
SGLS318 − NOVEMBER 2005 140 120 PHASE 100 −90 80 −45 60 −0 Phase − ° 100 Gain − dB Gain − dB 120 40 20 0 VOLTAGE AMPLIFIER GAIN vs FREQUENCY PHASE 120 100 80 80 60 60 40 40 20 20 0 0 −20 GAIN fCO = 5.
PAGE 11
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PAGE 13
IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete.