UCC3857N
UCC1857
UCC2857
UCC3857
PRELIMINARY
DESCRIPTION
The UCC3857 provides all of the control functions necessary for an Iso-
lated Boost PFC Converter. These converters have the advantage of trans-
former 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 pro-
vides a separate output to drive an external power MOSFET which pro-
vides 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 typi-
cally associated with these devices. This allows for higher switching fre-
quencies, smaller magnetic components and higher efficiency. The power
factor correction (PFC) portion of the UCC3857 employs the familiar aver-
age current control scheme used in previous Unitrode controllers. Internal
circuitry changes, however, have simplified the design of the PFC section
and improved performance.
(continued)
Isolated Boost PFC Preregulator Controller
8 154
VD
13 73
VINCAOCA–MOUTPKLMT
14MOSDRV
16IGDRV1
18IGDRV2
17
PGND
20
CT
6
AGND
19
RT
20
SS
5VREF
12DELAY
11 VAO
10 VA–
2
CRMS
1IAC
REF
REF
Z
V
Z
C
R
S
Q2Q1
T1
FEEDBACK
CKT
OPTO
BIAS
SUPPLY
QA
R
AC
V
OUT
+
–
RECTIFIED
AC INPUT
REF
UCC3857
C
F
TYPICAL APPLICATION CIRCUIT
FEATURES
• PFC With Isolation, V
O
< V
IN
• 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
02/99
UDG-98065
2
UCC1857
UCC2857
UCC3857
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 ter-
minal. 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 pack-
ages.
3
18
17
16
IAC
122019
15
14
4
5
6
7
8
91110 12 13
CRMS
MOUT
CT
RT
IGDRV2
PGND
IGDRV1
VD
MOSDRV
VIN
VREF
AGND
CA–
CAO
PKLMT
DELAY
VAO
SS
VA–
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 op-
erating current. The A-D converter eliminates an external
2 pole low pass filter for RMS detection.
This simplifies the converter design, eliminates 2nd har-
monic ripple from the feedforward component, and pro-
vides 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 reli-
able off-line startup, a programmable over current shut-
down, 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.
IGDRV2
RT
CT
PGND
IGDRV1
MOSDRV
VD
PKLMT
1
2
3
4
5
6
7
8
20
19
18
17
16
15
14
13
CRMS
IAC
CAO
AGND
CA–
MOUT
VIN
VREF
9
10VA–
SS DELAY
VAO
12
11
CONNECTION DIAGRAMS
DIL-20, SOIC- 20 (Top View)
J, N and DW Packages
PLCC-20 (Top View)
L Package
3
UCC1857
UCC2857
UCC3857
ELECTRICAL CHARACTERISTICS:
Unless otherwise stated, these specifications apply for T
A
= 0°C to 70°C for the
UCC3857, –40°C to +85°C for the UCC2857, and –55°C to +125°C for the UCC1857, V
VIN
, V
VD
= 12V, R
T
= 19.2K, C
T
= 680pF.
T
A
= T
J
.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITS
Input Supply
Supply Current, Active No Load on Outputs, V
VD
= V
VIN
3.5 5 mA
Supply Current, Startup No Load on Outputs, V
VD
= V
VIN
60 TBD µA
VIN UVLO Threshold 13.75 15.5 V
UVLO Threshold Hysteresis 3 3.75 TBD V
Reference
Output Voltage (V
VREF
)T
J
= 25°C, I
REF
= 1mA 7.387 7.5 7.613 V
Over Temperature, UCC3857 7.368 7.5 7.631 V
Over Temperature, UCC1857, UCC2857 7.313 7.5 7.687 V
Load Regulation I
REF
= 1mA to 10mA 2 10 mV
Line Regulation V
VIN
= V
VD
= 12V to 16V 2 15 mV
Short Circuit Current V
VREF
= 0V –55 –30 mA
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
CM
= 0V to 1.5V, V
CAO
= 3V 80 dB
AVOL V
CM
= 0V, V
CAO
= 2V to 5V 65 85 dB
VOH Load on CAO = 50µA, V
MOUT
= 1V, V
CA–
= 0V 6 7 V
VOL Load on CAO = 50µA, V
MOUT
= 0V, VCA– = 1V 0.2 V
Maximum Output Current Source : V
CA–
= 0V, V
MOUT
= 1V, V
CAO
= 3V –150 µA
Sink : V
CA–
= 1V, V
MOUT
= 0V, V
CAO
= 3V 5 30 50 mA
Gain Bandwidth Product f
IN
= 100kHz, 10mV p – p 3 5 MHz
Voltage Amplifier
Input Voltage Measured on V
VA–
,
V
VAO
= 3V 2.9 3 3.1 V
Input Bias Current Measured on V
VA–
,
V
VAO
= 3V –50 nA
AVOL V
VAO
= 1V to 5V 75 dB
VOH Load on V
VAO
= –50µA, V
VA–
= 2.8V 5.3 5.55 5.7 V
VOL Load on V
VAO
= 50µA, V
VA–
= 3.2V 0.1 0.45 V
Maximum Output Current Source: V
VA–
= 2.8V, V
VAO
= 3V –20 –12 –5 mA
Sink: V
VA–
= 3.2V, V
VAO
= 3V 5 20 30 mA
Oscillator
Initial Accuracy T
J
= 25°C 42.5 50 57.5 kHz
40 50 60 kHz
Voltage Stability V
VIN
= 12V to 18V 1 %
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
LOAD
= 1nF 25 TBD ns
Fall Time C
LOAD
= 1nF 10 TBD ns
Trailing Edge Delay
Delay Time R
D
= 12k, C
D
= 200pF, V
VAO
= 4V 1.6 2 2.4 µs
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