AN4027 datasheet(22/41 Pages) STMICROELECTRONICS

22 / 41 page

Functional check

AN4027

22/41

DocID022604 Rev 3

In Figure 24 and Figure 25 the transitions from full load to no load and vice versa have been

checked. As seen in the images, both transitions are clean and there isn't any output voltage

dip.

4.3

Overcurrent and short-circuit protection

The L6699 is equipped with a current sensing input (pin 6, ISEN) and a dedicated

overcurrent management system. The current flowing in the resonant tank is detected and

the signal is fed into the ISEN pin. It is internally connected to a first comparator, referenced

to 0.8 V, and to a second comparator referenced to 1.5 V. If the voltage externally applied to

the pin exceeds 0.8 V, the first comparator is tripped causing an internal switch to be turned

on and to discharge the soft-start capacitor CSS.

Under output short-circuit, this operation results in a nearly constant peak primary current.

With the L6699, the board designer can externally program the maximum time that the

Figure 22. Pout = 250 mW operation

Figure 23. Pout = 250 mW operation - detail

CH1: HB voltage

CH2: LVG

CH3: STBY

CH4: Vout (AC coupl.)

AM11624v1

CH1: HB voltage

CH2: LVG

CH3: STBY

CH4: Res. tank current

AM11625v1

Figure 24. Transition full load to no load at

115 Vac - 60 Hz

Figure 25. Transition no load to full load at

115 Vac - 60 Hz

CH1: LVG pin

CH2: PFC gate

CH3: Output voltage CH4: Output current

AM11626v1

CH1: LVG pin

CH2: PFC gate

CH3: Output voltage CH4: Output current

AM11627v1

AN4027 Datasheet(PDF) 22 Page - STMicroelectronics