Data Sheet

ManualsBrandsON SEMICONDUCTOR ManualsPMICsPMIC - AC/DC converter, offline switcher Flyback DIP 8

FSL206MR • Rev. 1.0.5 11

FSL206MR — Green Mode Fairchild Power Switch (FPS™)

Line Under-Voltage Protection (LUVP)

If the input voltage of the converter is lower than the

minimum operating voltage, the converter input current

increases too much, causing components failure. If the

input voltage is low, the converter should be protected.

In the FSL206MR, the LUVP circuit senses the input

voltage using the LS pin and, if this voltage is lower than

1.5V, the LUVP signal is generated. The comparator

has 0.5V hysteresis. If the LUVP signal is generated, the

output drive block is shut down and the output voltage

feedback loop is saturated.





Figure 21. Line UVP Circuit

Soft-Start

The FSL206MR has an internal soft-start circuit that

slowly increases the feedback voltage, together with the

SenseFET current, after it starts. The typical soft-start

time is 15ms, as shown in Figure 22, where progressive

increments of the SenseFET current are allowed during

the startup phase. The pulse width to the power

switching device is progressively increased to establish

the correct working conditions for transformers,

inductors, and capacitors. The voltage on the output

capacitors is progressively increased with the intention

of smoothly establishing the required output voltage. It

also helps prevent transformer saturation and reduce

the stress on the secondary diode.

Figure 22. Internal Soft-Start

Burst Operation

To minimize power dissipation in Standby Mode, the

FPS enters Burst Mode. As the load decreases, the

feedback voltage decreases. As shown in Figure 23, the

device automatically enters Burst Mode when the

feedback voltage drops below V

BURH

. Switching

continues until the feedback voltage drops below V

BURL

At this point, switching stops and the output voltages

start to drop at a rate dependent on the standby current

load. This causes the feedback voltage to rise. Once it

passes V

BURH

, switching resumes. The feedback voltage

then falls and the process repeats. Burst Mode

alternately enables and disables switching of the

SenseFET and reduces switching loss in Standby Mode.

BURL

BURH

set

time

Switching

disabled

t1 t2 t3

Switching

disabled

Figure 23. Burst-Mode Operation