Datasheet
SLUS579 − OCTOBER, 2003
8
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APPLICATION INFORMATION
The UCC3819A is based on the UCC3818 PFC preregulator. For a more detailed application information for
this part, please refer to the UCC3818 datasheet product folder.
The main difference between the UCC3818 and the UCC3819A is that the non-inverting input of the voltage
error amplifier is made available to the user through an external pin (VAI) in the UCC3819A. The SS pin and
function were eliminated to accommodate this change.
The benefit of VAI pin is that it can be used to dynamically change the PFC output voltage based on the line
voltage (RMS) level or other conditions. Figure 1 shows one suggested implementation of the tracking boost
PFC converter as this approach is sometimes referred to. The VAI pin is tied to the VFF pin and hence output
voltage scales up with the line voltage. The benefit of this approach is that at lower line voltages the output
voltage is lower and that leads to smaller boost inductor value, lower MOSFET conduction losses and reduced
component stresses. In order for this feature to work, the downstream converter has to operate over a wider
input range.
UDG−01008
1
11
7
16GND DRVOUT
R17
15
C3
C2
14
C1
13
C4
12
R1
R3
R2
R4
R5C5
9
4
10
V
REF
VCC
CT
VAI
RT
VSENSE
OVP/EN
VREF
VAOUT
3
8
2
VFF
C6
C7
R7
6
5
R9
C8
R8
D6
R10
D5
R11
R12
R14
C13C14
R13
IAC
D2
D1
C12
V
OUT
+
−
PKLIMIT
CAOUT
CAI
MOUT
IAC
V
O
UCC3819A
V
LINE
V
REF
C9
R6
D3
Q1
F1
V
O
D4
R19
R20
R21
AC2
AC1
C15
VFF
VCC (FROM BIAS SUPPLY)
Figure 1. Suggested Implementation of UCC3819A in a Tracking Boost PFC Preregulator