FAN6982 Fairchild Semiconductor, FAN6982 Datasheet - Page 13

• Manufacturer Part Number: FAN6982
• Description: The FAN6982 is a 14-pin, Continuous Conduction Mode (CCM) PFC controller IC intended for Power Factor Correction (PFC) pre-regulators
• Manufacturer: Fairchild Semiconductor

© 2009 Fairchild Semiconductor Corporation
FAN6982 • Rev. 1.0.3
I
The rectified sinusoidal signal is obtained by the current
flowing into the IAC pin. The resistor R
large enough to prevent saturation of the gain
modulator as:
where V
protection, G
V
current of the gain modulator.
Current-Control of Boost Stage
As shown in Figure 27 the FAN6982 employs two
control loops for power factor correction, a current-
control loop and a voltage-control loop. The current-
control loop shapes inductor current, as shown in
Figure 28, based on the reference signal obtained at
IAC pin as:
L
2
RMS
C
⋅
C
V
R
RMS1
R
RMS2
LINE BO
R
IAC
CS
RMS1
I
I
AC
MO
1
is 1.08V, and 159µA is the maximum output
.
=
R
R
Figure 28. Inductor Current Shaping
LINE.BO
I
CS
M
L
I
R
R
Figure 27. Gain Modulation Block
⋅
C
MO
RMS2
1
G
RMS3
V
VC2
IN
R
MAX
MAX
I
⋅
IAC
AC
R
is the line voltage that trips brownout
M
ISENSE
VRMS
VEA
C
<
is the maximum modulator gain when
IAC
R
F1
=
F1
R
C
159
VC
VC1
I
AC
μ
⋅ ⋅
I
A
L
R
G R
I
MO
CS1
R
R
M
M
M
+
-
2.5V
Drive
logic
IAC
V
O
C
IEA
FBPFC
RT/CT
VREF
OPFC
IC2
should be
R
C
IC
IC1
R
R
FB1
FB2
(3)
(4)
13
V
The current-control feedback loop also has a pulse-by-
pulse current limit comparator that forces the PFC
switch to turn off if the ISENSE pin voltage drops below
-1.15V until the next switching cycle.
Voltage-Control of Boost Stage
The voltage-control loop regulates PFC output voltage
using internal error amplifier such that the FBPFC
voltage is same as internal reference of 2.5V.
To improve system efficiency at low AC line voltage
and light-load condition, FAN6982 provides adjustable
PFC output voltage. As shown in Figure 29, FAN6982
monitors V
voltage. When V
internal current source of 20µA is enabled that flows
through R
This causes the PFC output voltage to reduce when
20µA is enabled as:
Brownout Protection
FAN6982 has a built-in internal brownout protection
comparator monitoring the voltage of the VRMS pin.
Once the VRMS pin voltage is lower than 1.05V, the
PFC stage is shutdown to protect the system from over
current. FAN6982 starts up the boost stage once the
VRMS voltage increases above 1.9V.
TriFault Detect™
To improve power supply reliability, reduce system
component count, and simplify compliance to UL 1950
safety standards; the FAN6982 includes TriFault Detect
technology. This feature monitors FBPFC for certain
PFC fault conditions.
In the case of a feedback path failure, the output of the
PFC could exceed operating limits. Should FBPFC go
too low, or too high, or open; TriFault Detect senses the
error and terminates the PFC output drive.
TriFault detect is an entirely internal circuit. It requires
no external components to serve its protective function.
OPFC
2
Figure 29. Block of Adjustable PFC Output
=
R
FB
FB2
1
R
EA
, increasing the voltage of the FBPFC pin.
+
FB
R
2
and V
FB
EA
2
and V
×
(2 5 20
RMS
. -
RMS
to adjust the PFC output
are lower than thresholds,
μA R
×
FB
2
)
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