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UC3854A中文资料

BLOCK DIAGRAM

?Controls Boost PWM to Near Unity Power Factor

?Limits Line Current Distortion To <3%?World-Wide Operation Without Switches ?Accurate Power Limiting

?Fixed Frequency Average Current Mode Control

?High Bandwidth (5MHz), Low Offset Current Amplifier

?Integrated Current and Voltage Amp Output Clamps

Multiplier Improvements: Linearity,

500mV VAC Offset (eliminates external resistor), 0-5V Multout Common Mode Range

?V REF "GOOD" Comparator

?Faster and Improved Accuracy ENABLE Comparator

?UVLO Threshold Options (16/10V / 10.5/10V)

300μA Startup Supply Current

The UC1854A/B products are pin compatible enhanced versions of the

UC1854. Like the UC1854, 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 UC1854A/B 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.

The UC1854A/B products improve upon the UC1854 by offering a wide bandwidth, low offset Current Amplifier, a faster responding and improved accuracy enable comparator, a V REF "good" comparator,UVLO threshold options (16/10V for offline, 10.5/10V for startup from an auxiliary 12V 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 Amp 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 AC at all times which simplifies the design process and provides foldback power limiting during brownout and extreme low line conditions.

A 1% 7.5V reference, fixed frequency oscillator, PWM, Voltage Amplifier with softstart, line voltage feedforward (V RMS squarer), input supply voltage clamp, and over current comparator round out the list of features.

UC2854A/B UC3854A/B

Enhanced High Power Factor Preregulator

FEATURES

DESCRIPTION

UVLO Turn on UVLO Turn off

UC1854A 16V 10V UC1854B

10.5V 10V

UDG-93001-1

DIL–16 & SOIC-16(Top View)

J, N & DW Packages

PACKAGE PIN FUNCTION

FUNCTION

N/C 1 Gnd 2PKLMT 3CA Out 4I SENSE 5N/C

6Mult Out 7I AC

8VA Out 9V RMS 10N/C 11V REF 12ENA 13V SENSE 14R SET 15N/C 16SS 17C T 18V CC 19GT Drv 20

PLCC-20 & LCC-20(Top View)

Q & L Packages

CONNECTION DIAGRAMS

Supply Voltage V CC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22V GT Drv Current, Continuous. . . . . . . . . . . . . . . . . . . . . . . 0.5A GT Drv Current, 50% Duty Cycle. . . . . . . . . . . . . . . . . . . . 1.5A Input Voltage, V SENSE , V RMS . . . . . . . . . . . . . . . . . . . . . . . 11V Input Voltage, I SENSE , Mult Out . . . . . . . . . . . . . . . . . . . . . 11V Input Voltage, PKLMT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5V Input Current, R SET , I AC , PKLMT, ENA . . . . . . . . . . . . . . 10mA Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1W Storage Temperature . . . . . . . . . . . . . . . –65°C to +150°C Lead Temperature (Soldering, 10 Seconds). . . . . . . . . +300°C

ABSOLUTE MAXIMUM RATINGS

Note 1: All voltages with respect to Gnd (Pin 1).

Note 2: All currents are positive into the specified terminal.Note 3: ENA imput is internally clamped to approximately 10V.Note 4: Consult Unitrode Integrated Circuits databook for information regarding thermal specifications and limitations of packages.

PARAMETER

TEST CONDITIONS

MIN

TYP MAX UNITS OVERALL

Supply Current, Off CAO, VAO = 0V, V CC = UVLO - 0.3V 250400μA Supply Current, On 1218mA V CC Turn-On Threshold UC1854A 1617.5V UC1854B 10.511.2V V CC Turn-Off Threshold UC1854A / B

910V V CC Clamp

I(V CC ) = I CC (on) + 5mA

182022V VOLTAGE AMPLIFIER Input Voltage

2.9

3.0 3.1V V SENSE Bias Current –500–25500

nA Open Loop Gain V OUT = 2 to 5V 70

100dB V OUT High I LOAD = –500μA 6V V OUT Low

I LOAD = 500μA 0.30.5V Output Short Circuit Current V OUT = 0V

1.5 3.5

mA Gain Bandwidth Product

Fin = 100kHz, 10mV p-p, (Note 1)

mHz

Unless otherwise stated, V CC =18V, R T =8.2k, C T =1.5nF, PKLMT=1V, V RMS =1.5V,I AC =100μA, I SENSE =0V, CA Out=3.5V, VA Out=5V, V SENSE =3V, –55o C

for the UC1854A/B, –40o C

ELECTRICAL CHARACTERISTICS

ELECTRICAL

CHARACTERISTICS (cont.)PARAMETER

TEST CONDITIONS MIN TYP

MAX UNITS CURRENT AMPLIFIER Input Offset Voltage V CM = 0V

T A = +25°C ?40mV OverTemp

–5.50mV Input Bias Current(sense)V CM = 0V

–500500

nA Open Loop Gain V CM = 0V, V OUT = 2 to 6V 80

110dB V OUT High I LOAD = –500μA 8V V OUT Low

ILOAD = 500μA 0.30.5V Output Short Circuit Current V OUT = 0V

1.5 3.5mA Common Mode Range –0.35

V Gain Bandwidth Product Fin = 100kHz, 10mV p-p, (Note 1)35mHz REFERENCE Output Voltage I REF = 0mA, T A = 25o C 7.47.57.6V I REF = 0mA

7.357.57.65V Load Regulation I REF = 1 to 10mA 0820mV Line Regulation

V CC = 12 to 18V 01425mV Short Circuit Current

V REF = 0V 253560mA OSCILLATOR Initial Accuracy T A = 25o C

85100115kHz Voltage Stability V CC = 12 to 18V 1

%Total Variation

Line, Temp

80120kHz Ramp Amplitude (p-p) 4.9 5.9V Ramp Valley Voltage

0.8 1.3

V ENABLE / SOFTSTART / CURRENT LIMIT Enable Threshold 2.35

2.55 2.8V Enable Hysteresis V FAULT = 2.5V

500600mV Enable Input Bias Current V ENABLE = 0V

–2–5μA Propagation Delay to Disable Enable Overdrive = –100mV,(Note 1)300ns SS Charge Current V SOFTSTART = 2.5V 101424PKLMT Offset Voltage –1515

mV PKLMT Input Current V PKLMT = –0.1V –200

–100μA PKLMT Propagation Delay (Note 1)

150ns MULTIPLIER

Output Current - I AC Limited I AC =100μA, V RMS = 1V, R SET = 10k –220–200–170μA Output Current - Zero

I AC =0μA, R SET = 10k –2.0–0.2 2.0μA Output Current - Power Limited V RMS = 1.5V, Va = 6V –230

–200–170μA Output Current

V RMS = 1.5V, Va = 2V –22μA V RMS = 1.5V, Va = 5V –156μA V RMS = 5V, Va = 2V –2μA V RMS = 5V, Va = 5V

–14μA Gain Constant (Note 2) V RMS = 1.5V, T J = 25°C, Va = 6V

–1.1–1.0

–0.9

A/A

Unless otherwise stated, V CC =18V, R T =8.2k, C T =1.5nF, PKLMT=1V, V RMS =1.5V,I AC =100μA, I SENSE =0V, CA Out=3.5V, VA Out=5V, V SENSE =3V, –55o C

Note 1: Guaranteed by design, not 100% tested in production.

Note 2: Gain constant (K) = I AC × (Va ? 1.5V )

V RMS 2 × I MO

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS GATE DRIVER

Output High Voltage I OUT = –200mA, V CC = 15V1212.8V Output Low Voltage I OUT = 200mA1 2.2V

I OUT = 10mA300500mV

Output Low (UVLO)I OUT = 50mA, V CC = 0V0.9 1.5V Output Rise / Fall Time C LOAD = 1nF, (Note 1)35ns Output Peak Current C LOAD = 10nF, (Note 1) 1.0A

Note 1: Guaranteed by design, not 100% tested in production.

Note 2: Gain constant (K) = I AC×(Va? 1.5V) V RMS2×I MO

ELECTRICAL CHARACTERISTICS (cont.)Unless otherwise stated, V CC=18V, R T=8.2k, C T=1.5nF, PKLMT=1V, V RMS=1.5V, I AC=100μA, I SENSE=0V, CA Out=3.5V, VA Out=5V, V SENSE=3V, –55o C

–40o C

The UC1854A/B products were designed as pin compatible upgrades to the industry standard UC1854 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 UC1854. In addition, linearity improvements to the Multiply, Square, and Divide circuitry optimizes overall system performance. Detailed descriptions of the circuit enhancements are provided below. For in-depth design applications reference data refer to Unitrode application notes U-134 and DN-44. MULTIPLY / SQUARE AND DIVIDE

The UC1854A/B Multiplier design maintains the same gain constant (K = ?1), as the UC1854. The relationship between the inputs and output current is given as:

I MO = I AC(V AO - 1.5V) / K?V RMS2

This is nearly the same as the UC1854, but circuit differences have improved the performance and application.

The first difference is with the I AC input. The UC1854A/B regulates this pin voltage to a nominal 500mV over the full operating temperature range, rather than the 6.0V used on the UC1854. This low offset voltage eliminates the need for a line zero crossing compensating resistor to V REF from I AC that UC1854 designs require. The maximum current at high line into I AC should be limited to 250μA for best performance. Therefore, if V AC (max) = 270V, then R AC = 270(1.414) / 250μA = 1.53M?.

The V RMS pin linear operating range is improved with the UC1854A/B as well. The input range for V RMS extends from 0 to 5.5V. Since the UC1854A squaring circuit employs an analog multiplier, rather than a linear approximation, accuracy is improved, and discontinuities are eliminated. The external divider network connected to V RMS should produce 1.5V at low line (85VAC). This will put 4.77V on V RMS at high line (27VAC) which is well within its operating range.

The Voltage Amplifier output forms the third input to the Multiplier and is internally clamped to 6.0V. This eliminates an external zenerclamp often used in UC1854 designs. The offset voltage at this input to the Multiplier has been raised on the UC1854A/B to 1.5V.

The Multiplier output pin, which is also common to the Current Amplifier non-inverting input, has a ?0.3V to 5.0V output range,compared to the ?0.3 to 2.5V range of the UC1854. This improvement allows the UC1854A/B to be used in applications where the current sense signal amplitude is very large.

VOLTAGE AMPLIFIER

The UC1854A/B Voltage Amplifier design is essentially similar to the UC1854 with two exceptions. The first is with the internal connection. The lower voltage reduces the amount of charge on the compensation capacitor, which provides improved recovery from large signal events, such as line dropouts, or power interruption. It also minimizes the DC current flowing through the feedback. The output of the Voltage amplifier is also changed. In addition to a 6.0V temperature compensated clamp, the output short circuit current has been lowered to 2mA typical, and an active pull down has replaced the passive pulldown of the UC1854.

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 UC1854A/B Current Amplifier has improved the input offset voltage from ±4mV to 0 to ?3mV. The negative

FUNCTIONAL DESCRIPTION

offset of the UC1854A/B guarantees that the PWM circuit will not drive the MOSFET if the current command is zero (both Current amplifier inputs zero.).Previous designs required an external offset cancellation network to implement this key feature. The bandwidth of the Current Amplifier has been improved as well to 5mHz typical.While this is not generally an issue at 50 or 60Hz inputs, it is essential for 400Hz input avionics applications.

MISCELLANEOUS Several other important enhancements have been implemented in the UC1854A/B. A V CC supply voltage clamp at 20V allows the controller to be current fed if desired. The lower startup supply current (250μA typical),substantially reduces the power requirements of an offline startup resistor. The 10.5/10V UVLO option (UC1854B)enables the controller to be powered off of an auxiliary 12V supply.

The V REF "GOOD" comparator guarantees that the MOSFET driver output remains low if the supply or the 7.5V reference are not yet up. This improvement

eliminates the need for external Schottky diodes on the PKL and CA+ pins that some UC1854 designs require.The propagation delay of the disable feature has been improved to 300ns typical. This delay was proportional to

FUNCTIONAL DESCRIPTION (cont.)

TYPICAL CHARACTERISTICS at T A = T J = 25°C

Load Capacitance,μF ns

0100200300400500

6007000

0.01

0.02

0.03

0.04

0.05

Rise Time

Fall Time

Gate Drive Rise and Fall Time

R SET , k ?

Duty

Cycle

70%

75%80%85%

90%

95%100%1

100

Gate Drive Maximum Duty Cycle

50100150200250

0.8

0.840.880.920.9611.041.081.121.161.2K

I AC Current (μA)

V RMS =1.5V

V RMS =3.0V

V RMS =5.0V

UC1854A/B Multiplier Linearity

VA OUT = 3.5V

100150200250

0.8

0.840.880.920.9611.041.081.121.161.2K

I AC Current (μA)

V RMS =3.0V

V RMS =1.5V

V RMS =5.0V

UC1854A/B Multiplier Linearity

VA OUT = 5V

TYPICAL CHARACTERISTICS at T A = T J = 25°C (cont.)

UNITRODE CORPORATION

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

These products contain patented circuitry and are sold under license from Pioneer Magnetics, Inc.

log f

G a i n (d B )

-60

-40

-2002040600

80-45Phase

Degrees

100

-90

12010kHz

1MHz

10MHz

100kHz

Gain

Phase

5.992 496 516 MHz

Current Amplifier Frequency Response

R SET , k ?

Frequency kHz 10

100

1000

110100

100pF 200pF 5nF 10nF 3nF 500pF 2nF

1nF

Oscillator Frequency vs R SET and C T

Frequency

kHz

Phase Margin degrees

Open-Loop Gain

dB -200

2040

801001200.1

100

1000

10000

Voltage Amplifier Gain and Phase vs Frequency

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