TEA1751T_LT_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 23 December 2009

8 of 29

NXP Semiconductors

TEA1751T; TEA1751LT

GreenChip III SMPS control IC

7.1.4 Fast latch reset

In a typical application the mains can be interrupted briefly to reset the latched protection.

reset.

level. When the latched protection is set, the clamping circuit of the VINSENSE circuit is

disabled. (see also Section 7.2.9) As soon as the VINSENSE voltage drops below

750 mV (typical) and after that is raised to 870 mV (typical), the latched protection is reset.

pin HV.

7.1.5 Overtemperature protection

An accurate internal temperature protection is provided in the circuit. When the junction

temperature exceeds the thermal shutdown temperature, the IC stops switching. As long

on pin HV or by the fast latch reset function. (See Section 7.1.4)

7.2 Power factor correction circuit

The power factor correction circuit operates in quasi-resonant or discontinuous

conduction mode with valley switching. The next primary stroke is only started when the

previous secondary stroke has ended and the voltage across the PFC MOSFET has

reached a minimum value. The voltage on the PFCAUX pin is used to detect transformer

demagnetization and the minimum voltage across the external PFC MOSFET switch.

reduction of a typical application is well within the class-D requirements.

7.2.2 Valley switching and demagnetization (PFCAUX pin)

The PFC MOSFET is switched on after the transformer is demagnetized. Internal circuitry

connected to the PFCAUX pin detects the end of the secondary stroke. It also detects the

voltage across the PFC MOSFET. The next stroke is started when the voltage across the

PFC MOSFET is at its minimum in order to reduce switching losses and ElectroMagnetic

Interference (EMI) (valley switching).

If no demagnetization signal is detected on the PFCAUX pin, the controller generates a

zero current signal (ZCS), 50

μs (typical) after the last PFCGATE signal.

If no valley signal is detected on the PFCAUX pin, the controller generates a valley signal

4

μs (typical) after demagnetization was detected.

To protect the internal circuitry during lightning events, for example, it is advisable to add a

5k

Ω series resistor to this pin. To prevent incorrect switching due to external disturbance,

the resistor should be placed close to the IC on the printed-circuit board.