TEA1750T/N1,518【PDF 15/29 页】IC PFC CONTROLLER DCM16SOIC

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Sheet目录46

11页 12页 13页 14页 [15页]16页 17页 18页 19页

TEA1750_2

Product data sheet

Rev. 02 15 December 2008

15 of 29

NXP Semiconductors

TEA1750

GreenChip III SMPS control IC

The driver output is latched in the logic, preventing multiple switch-on.

7.3.4 Demagnetization (FBAUX pin)

The system is always in quasi-resonant or discontinuous conduction mode. The internal

oscillator does not start a new primary stroke until the previous secondary stroke has

ended.

Demagnetization features a cycle-by-cycle output short-circuit protection by immediately

lowering the frequency (longer off-time), thereby reducing the power level.

Demagnetization recognition is suppressed during the rst t

sup(xfmr_ring)

time (2 祍 typ).

This suppression may be necessary at low output voltages and at start-up and in

applications where the transformer has a large leakage inductance.

If pin FBAUX is open-circuit or not connected, a fault condition is assumed and the

converter stops operating immediately. Operation restarts as soon as the fault condition is

removed.

7.3.5 Flyback control / time-out (FBCTRL pin)

The pin FBCTRL is connected to an internal voltage source of 3.5 V via an internal

resistor (typical resistance is 3 k&). As soon as the voltage on this pin is above 2.5 V (typ),

this connection is disabled. Above 2.5 V the pin is biased with a small current. When the

voltage on this pin rises above 4.5 V (typ), a fault is assumed and switching is inhibited.

When a small capacitor is connected to this pin, a time-out function can be created to

protect against an open control loop situation (see

Figure

11 and

Figure

12). The time-out

function can be disabled by connecting a resistor (100 k&) to ground on the FBCTRL pin.

If the pin is shorted to ground, switching of the yback controller is inhibited.

In normal operating conditions, when the converter is regulating the output voltage, the

voltage on the FBCTRL pin is between 1.4 V and 2.0 V (typical values) from minimum to

maximum output power.

Fig 10. Frequency control of yback part

sense(fb)max

FBCTRL

1.5 V

2.0 V

0.52 V

flyback

frequency

reduction

PFC burst mode

FBSENSE peak voltage

014aaa028

PFC on

flyback

discontinuous

or QR

flyback

cycle skip

mode

1.4 V

0.13 V

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