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TEA1751T/1791/DB/9

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P31
TEA1751T All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 10 January 2013 10 of 31
NXP Semiconductors
TEA1751T
HV start-up flyback controller with integrated PFC controller
7.2.3 Frequency limitation
To optimize the transformer and minimize switching losses, the switching frequency is
limited to f
sw(PFC)max
. If the frequency for quasi-resonant operation is above the f
sw(PFC)max
limit, the system switches over to DCM. The PFC MOSFET is only switched on at a
minimum voltage across the switch (valley switching).
7.2.4 Mains voltage compensation (VINSENSE pin)
The 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 and a high bandwidth for high mains input voltages.
To compensate for the mains input voltage influence, the TEA1751T contains a correction
circuit. The average input voltage is measured using the VINSENSE pin and the
information is fed to an internal compensation circuit. Using this compensation, it is
possible to keep the regulation loop bandwidth constant over the mains input range. This
feature yields a fast transient response on load steps, while still complying with class-D
MHR requirements.
In a typical application, a resistor and two capacitors connected to the PFCCOMP pin set
the bandwidth of the regulation loop.
7.2.5 Soft-start-up (pin PFCSENSE)
To prevent audible transformer noise at start-up or during hiccup, the soft-start function
slowly increases the transformer peak current. This increase is achieved by inserting R
SS1
and C
SS1
between the PFCSENSE pin and the current sense resistor R
SENSE1
.
An internal current source charges the capacitor to:
(1)
The voltage is limited to V
start(soft)PFC
.
The start level and the time constant of the increasing primary current level are adjusted
externally by changing the values of R
SS1
and C
SS1
.
(2)
The charging current I
start(soft)PFC
flows as long as V
PFCSENSE
is below 0.5 V. If V
PFCSENSE
exceeds 0.5 V, the soft-start current source starts limiting current I
start(soft)PFC
. When the
PFC starts switching, the I
start(soft)PFC
current source is switched off; see Figure 5.
V
PFCSEN SE
I
start softPFC
R
SS1
=
TEA1751T All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 10 January 2013 11 of 31
NXP Semiconductors
TEA1751T
HV start-up flyback controller with integrated PFC controller
7.2.6 Low-power mode
When the output power of the flyback converter (see Section 7.3) is low, the flyback
converter switches over to frequency reduction mode. The power factor correction circuit
is then switched off to maintain high efficiency.
During low-power mode operation, the PFCCOMP pin is clamped to a minimum voltage of
2.7 V and a maximum voltage of 3.9 V. The lower clamp voltage limits the maximum
power that is delivered when the PFC is switched on again. The upper clamp voltage
ensures that the PFC returns to its normal regulation point in a limited time when returning
from low-power mode.
When the flyback converter leaves the frequency reduction mode, the power factor
correction circuit restores normal operation. To prevent continuous switching of the PFC
circuit, a small hysteresis is built in (75 mV on the FBCTRL pin).
7.2.7 Dual-boost PFC
The mains input voltage modulates the PFC output voltage. The mains input voltage is
measured using the VINSENSE pin. If the voltage on the VINSENSE pin drops below
2.2 V, the current is sourced from the VOSENSE pin. To ensure the stable switch-over, a
200 mV transition region is inserted around the 2.2 V, see Figure 6
.
At low VINSENSE input voltages, the output current is 15 A. This output current, in
combination with the resistors on the VOSENSE pin, sets the lower PFC output voltage
level at low mains voltages. At high mains input voltages, the current is switched to zero.
The PFC output voltage is then at its maximum. As this current is zero in this situation, it
does not affect the accuracy of the PFC output voltage.
To ensure proper switch-off, the VOSENSE current switches to its maximum value of
15 A when the voltage on pin VOSENSE drops below 2.1 V.
Fig 5. Soft-start-up of PFC
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TEA1751T All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 10 January 2013 12 of 31
NXP Semiconductors
TEA1751T
HV start-up flyback controller with integrated PFC controller
7.2.8 Overcurrent protection (PFCSENSE pin)
The maximum peak current is limited cycle-by-cycle by sensing the voltage across an
external sense resistor, R
SENSE1
, on the source of the external MOSFET. The voltage is
measured via the PFCSENSE pin.
7.2.9 Mains undervoltage lockout/brownout protection (VINSENSE pin)
To prevent the PFC from operating at very low mains input voltages, the voltage on the
VINSENSE pin is continuously sensed. When the voltage on this pin drops below the
V
stop(VINSENSE)
level, switching of the PFC is stopped.
The voltage on the VINSENSE pin is clamped to a minimum value, V
start(VINSENSE)
V
pu(VINSENSE)
. This voltage clamping provides for a fast restart when the mains input
voltage is restored after a mains dropout.
7.2.10 Overvoltage protection (VOSENSE pin)
To prevent output overvoltage during load steps and mains transients, an overvoltage
protection circuit is built in.
When the voltage on the VOSENSE pin exceeds the V
OVP(VOSENSE)
level, switching of the
power factor correction circuit is stopped. Switching of the PFC recommences when the
VOSENSE pin voltage drops to less than V
OVP(VOSENSE)
again.
When the resistor between the VOSENSE pin and ground is open, the overvoltage
protection is also triggered.
7.2.11 PFC open-loop protection (VOSENSE pin)
The power factor correction circuit does not start switching until the voltage on the
VOSENSE pin exceeds the V
th(ol)(VOSENSE)
level. This feature protects the circuit from
open-loop and VOSENSE short-circuit.
7.2.12 Driver (PFCDRIVER pin)
The driver circuit to the gate of the power MOSFET has a current sourcing capability of
500 mA and a current sink capability of 1.2 A. These capabilities permit fast turn-on and
turn-off of the power MOSFET for efficient operation.
Fig 6. Voltage to current transfer function for dual boost PFC
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TEA1751T/1791/DB/9

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NXP Semiconductors
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Power Management IC Development Tools TEA1751 demoboard
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