AN10881
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© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 26 September 2011
35 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
7.2 PFC regulation
7.2.1 Sensing V
BOOST
The boost output voltage value is set with a resistor divider between the PFC output
voltage and pin SNSBOOST. When in regulation, the SNSBOOST voltage is kept at 2.5 V.
The resistor divider can have a total value up to 10 M
to limit power loss.
The measurement resistor between SNSBOOST and ground can be calculated with the
following equation:
(6)
Example:
•
R
measure(RBOOST)
= 4.7 M
+ 4.7 M
= 9.4 M
•
V
BOOST
= 394 V
(7)
Use a capacitor on SNSBOOST to prevent wrong measurements due to MOSFET
switching noise, mains surge events or ESD events. Also, for this reason, place the
measurement resistor and the filtering capacitor close to the IC in the PCB layout.
7.2.2 SNSBOOST open and short circuit pin detection
The PFC does not start switching until the voltage on SNSBOOST is above 0.4 V. This
serves as short circuit protection for the boost voltage and SNSBOOST pin itself.
An internal current source draws a small amount of current from SNSBOOST. This
prevents switching when the pin is left open as the voltage remains lower than 0.4 V. This
combination also creates an Open-Loop Protection (OLP) when, for example, one of the
resistors in the boost divider network is disconnected.
1.The TEA1713 PFC, operates in Quasi Resonant (QR) mode with valley detection providing good efficiency. Valley detection
needs additional ringing time within every switching cycle. This time for ringing adds short periods of no power transfer to the
output capacitor. The system must compensate this with a somewhat higher peak current. A rule of thumb is that the peak current
in QR mode is a maximum of 10 % higher than the calculated peak current in Critical conduction mode.
Fig 16. PFC output regulation example: SNSBOOST
001aal026
4.7 M
Ω
4.7 M
Ω
4.7 nF
Rmeasure(SNSBOOST)
60 k
Ω
24
SNSBOOST
PFC stage
VBOOST
R
BOOST
TEA1713
R
measure SNSBOOST
R
BOOST
V
reg SNSBOOST
V
BOOST
V
reg SNSBOOST
–
----------------------------------------------------------------
=
R
measure SNSBOOST
R
BOOST
V
reg SNSBOOST
V
BOOST
V
reg SNSBOOST
–
----------------------------------------------------------------
9.4
M
2.5
V
394
V
2.5
V
–
---------------------------------------
60
k
=
=
=