tea1752t NXP Semiconductors, tea1752t Datasheet - Page 10

• Manufacturer Part Number: tea1752t
• Description: Greenchip Iii Smps Control Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1752T_LT
Product data sheet
7.2.3 Frequency limitation
7.2.4 Mains voltage compensation (VINSENSE pin)
7.2.5 Soft start-up (pin PFCSENSE)
It is advisable to add a 5 kΩ series resistor to this pin to provide surge protection for the
internal circuitry against events such as lightning surge. To prevent incorrect switching
due to external disturbance, this resistor should be placed as close as possible to the IC
on the printed-circuit board.
To optimize the transformer and minimize switching losses, the switching frequency is
limited to f
limit, the system switches over to discontinuous conduction mode. The PFC MOSFET is
then only switched on at a minimum voltage across the switch (valley switching).
The mathematical equation for the transfer function of a power factor corrector contains
the square of the mains input voltage. In a typical application this results in a low
bandwidth for low mains input voltages, while at high mains input voltages the Mains
Harmonic Reduction (MHR) requirements may be hard to meet.
The TEA1752(L)T incorporates a correction circuit to compensate for the mains input
voltage influence. The average input voltage is measured via the VINSENSE pin and this
information is fed to an internal compensation circuit. With this compensation it is possible
to keep the regulation loop bandwidth constant over the full mains input range, yielding a
fast transient response on load steps, while still complying with class-D MHR
requirements.
In a typical application, the regulation loop bandwidth is set by a resistor and two
capacitors on the PFCCOMP pin.
To prevent audible transformer noise at start-up or during hiccup, the transformer peak
current is increased slowly by the soft start function. This can be achieved by inserting
R
An internal current source charges the capacitor to V
voltage is limited to V
The start level and time constant of the increasing primary current level can be adjusted
externally by changing the values of R
The charging current I
0.5 V (typical). If the voltage on pin PFCSENSE exceeds 0.5 V, the soft start current
source limits current I
source is switched off (see
Resistor R
switched off by performing a soft stop.
τsoftstart
SS1
and C
sw(PFC)max
SS1
=
SS1
3
and capacitor C
×
between pin PFCSENSE and the current sense resistor, R
All information provided in this document is subject to legal disclaimers.
R
SS1
. If the frequency for quasi-resonant operation is above the f
start(soft)PFC
start(soft)PFC
×
start(soft)PFC
Rev. 02 — 24 June 2010
C
SS1
Figure
SS1
.
. When the PFC starts switching, the I
flows if the voltage on pin PFCSENSE is lower than
are also used to prevent audible noise, when the PFC is
5).
SS1
TEA1752T; TEA1752LT
and C
SS1
.
PFCSENSE
GreenChip III SMPS control IC
= I
start(soft)PFC
start(soft)PFC
© NXP B.V. 2010. All rights reserved.
SENSE1
× R
sw(PFC)max
SS1
.
current
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. The