UNITRODE UCC1857, UCC2857, UCC3857 Technical data

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Isolated Boost PFC Preregulator Controller

UCC1857
UCC2857
UCC3857

PRELIMINARY

FEATURES

• PFC With Isolation, V

• Single Power Stage

• Zero Current Switched IGBT

• Programmable ZCS Time

• Corrects PF to >0.99

• Fixed Frequency, Average Current

Control

• Improved RMS Feedforward

• Soft Start

• 9V to 18V Supply V Range

• 20-Pin DW, N, J, and L Packages

< V

O

IN

TYPICAL APPLICATION CIRCUIT

DESCRIPTION

The UCC3857 provides all of the control functions necessary for an Iso­lated Boost PFC Converter. These converters have the advantage of trans­former isolation between primary and secondary, as well as an output bus
voltage that is lower than the input voltage. By providing both power factor
correction and down conversion in a single power processing stage, the
UCC3857 is ideal for applications which require high efficiency, integration,
and performance.

The UCC3857 brings together the control functions and drivers necessary
to generate overlapping drive signals for external IGBT switches, and pro­vides a separate output to drive an external power MOSFET which pro­vides zero current switching (ZCS) for both the IGBTs. Full programmability
is provided for the MOSFET driver delay time with an external RC network.
ZCS for the IGBT switches alleviates the undesirable turn off losses typi­cally associated with these devices. This allows for higher switching fre­quencies, smaller magnetic components and higher efficiency. The power
factor correction (PFC) portion of the UCC3857 employs the familiar aver­age current control scheme used in previous Unitrode controllers. Internal
circuitry changes, however, have simplified the design of the PFC section
and improved performance.

(continued)

RECTIFIED
AC INPUT

R

REF

CKT

+

C

F

V

OUT

–

T1

BIAS

SUPPLY

R

S

REF

AC

Z

V

13 73

1IAC

2

CRMS

10 VA–

11 VAO

5VREF

SS

20

UCC3857

RT
19

Z

C

8 154

VINCAOCA–MOUTPKLMT

PGND

CT

20

AGND

17

QA

VD

14MOSDRV

16IGDRV1

18IGDRV2

12DELAY

6

Q2Q1

FEEDBACK

OPTO

REF

02/99

UDG-98065

ABSOLUTE MAXIMUM RATINGS

Input Supply Voltage (VIN, VD). . . . . . . . . . . . . . . . . . . . . . 18V

General Analog/Logic Inputs

(CRMS, MOUT, CA–, VA–, CT, RT, PKLMT)

(Maximum Forced Voltage). . . . . . . . . . . . . . . . –0.3V to 5V

IAC (Maximum Forced Current) . . . . . . . . . . . . . . . . . . . 300µA

Reference Output Current . . . . . . . . . . . . . . . Internally Limited

Output Current (MOSDRV, IGDRV1, IGDRV2)

Pulsed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1A

Continuous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200mA

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

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

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

Unless otherwise indicated, voltages are reference to ground
and currents are positive into, negative out of the specified ter­minal. Pulsed is defined as a less than 10% duty cycle with a
maximum duration of 500 s. Consult Packaging Section of
Databook for thermal limitations and considerations of pack­ages.

UCC1857
UCC2857
UCC3857

DESCRIPTION (continued)

Controller improvements include an internal 6 bit A-D
converter for RMS input line voltage detection, a zero
load power circuit, and significantly lower quiescent op­erating current. The A-D converter eliminates an external
2 pole low pass filter for RMS detection.

This simplifies the converter design, eliminates 2nd har­monic ripple from the feedforward component, and pro­vides an approximate 6 times improvement in input line
transient response. The zero load power comparator
prevents energy transfer during open load conditions
without compromising power factor at light loads. Low
startup and operating currents which are achieved
through the use of Unitrode's BCDMOS process simplify
the auxiliary bootstrap supply design.

Additional features include: under voltage lockout for reli­able off-line startup, a programmable over current shut­down, an auxiliary shutdown port, a precision 7.5V
reference, a high amplitude oscillator ramp for improved
noise immunity, softstart, and a low offset analog square,
multiple and divide circuit. Like previous Unitrode PFC
controllers, worldwide operation without range switches
is easily implemented.

CONNECTION DIAGRAMS

DIL-20, SOIC- 20 (Top View)
J, N and DW Packages

IAC

1

2

CRMS

MOUT

3

4

VIN

5

VREF

6

AGND

7

CA–

CAO

8

9

SS DELAY

10VA–

20

19

18

17

16

15

14

13

12

11

CT

RT

IGDRV2

PGND

IGDRV1

VD

MOSDRV

PKLMT

VAO

PLCC-20 (Top View)
L Package

IAC
CRMS
MOUT

3

VIN

VREF

AGND

CA–

CAO

VA–

4
5
6
7
8

91110 12 13

SS

122019

18
17
16
15
14

CT
RT

IGDRV2
PGND
IGDRV1
VD
MOSDRV

PKLMT
DELAY
VAO

2

UCC1857
UCC2857
UCC3857

ELECTRICAL CHARACTERISTICS:

UCC3857, –40°C to +85°C for the UCC2857, and –55°C to +125°C for the UCC1857, V

Unless otherwise stated, these specifications apply for TA= 0°C to 70°C for the

, VVD= 12V, RT= 19.2K, CT= 680pF.

VIN

TA= TJ.

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

Input Supply

Supply Current, Active No Load on Outputs, V
Supply Current, Startup No Load on Outputs, V

VD
VD

= V
= V

VIN
VIN

3.5 5 mA
60 TBD µA

VIN UVLO Threshold 13.75 15.5 V
UVLO Threshold Hysteresis 3 3.75 TBD V

Reference

Output Voltage (V

)T

VREF

= 25°C, I

J

= 1mA 7.387 7.5 7.613 V

REF

Over Temperature, UCC3857 7.368 7.5 7.631 V

Over Temperature, UCC1857, UCC2857 7.313 7.5 7.687 V
Load Regulation I
Line Regulation V
Short Circuit Current V

= 1mA to 10mA 2 10 mV

REF

= VVD= 12V to 16V 2 15 mV

VIN

= 0V –55 –30 mA

VREF

Current Amplifier

Input Offset Voltage (Note 1) –3 0 3 mV
Input Bias Current (Note 1) –50 nA
Input Offset Current (Note 1) 25 nA
CMRR V
AVOL VCM= 0V, V

= 0V to 1.5V, V

CM

= 2V to 5V 65 85 dB

CAO

VOH Load on CAO = 50µA, V
VOL Load on CAO = 50µA, V
Maximum Output Current Source : V

Sink : V

CA–

= 0V, V

CA–

= 1V, V

= 3V 80 dB

CAO

MOUT

MOUT

= 1V, V

MOUT

= 0V, VCA– = 1V 0.2 V

MOUT

= 1V, V

= 0V, V

CAO

= 0V 6 7 V

CA–

= 3V –150 µA

CAO

= 3V 5 30 50 mA

Gain Bandwidth Product fIN= 100kHz, 10mV p – p 3 5 MHz

Voltage Amplifier

,

V

Input Voltage Measured on V
Input Bias Current Measured on V
AVOL V
VOH Load on V
VOL Load on V
Maximum Output Current Source: V

= 1V to 5V 75 dB

VAO

VAO

VAO

VA–

Sink: V

VA–

= 3.2V, V

VA–
VA–

= –50µA, V

= 50µA, V

= 2.8V, V

= 3V 2.9 3 3.1 V

VAO

,

V

= 3V –50 nA

VAO

= 2.8V 5.3 5.55 5.7 V

VA–

= 3.2V 0.1 0.45 V

VA–

= 3V –20 –12 –5 mA

VAO

= 3V 5 20 30 mA

VAO

Oscillator

Initial Accuracy T

= 25°C 42.5 50 57.5 kHz

J

40 50 60 kHz

Voltage Stability V

= 12V to 18V 1 %

VIN

CT Ramp Peak-Valley Amplitude 4 4.5 5 V
CT Ramp Valley Voltage 1.5 V

Output Drivers

VOH IL = –100mA 9 10 V
VOL IL = 100mA 0.1 0.5 V
Rise Time C
Fall Time C

= 1nF 25 TBD ns

LOAD

= 1nF 10 TBD ns

LOAD

Trailing Edge Delay

Delay Time R

= 12k, CD= 200pF, V

D

= 4V 1.6 2 2.4 µs

VAO

3