L6599AD datasheet(5/35 Pages) STMICROELECTRONICS

5 / 35 page

L6599A

Pin connection

Doc ID 15308 Rev 7

5/35

Pin connection

Figure 2.

Pin connection (top view)

Table 2.

Pin description

Pin N#

Type

Function

1Css

Soft-start. This pin connects an external capacitor to GND and a resistor to

RFmin (pin 4) that set both the maximum oscillator frequency and the time

constant for the frequency shift that occurs as the chip starts up (soft-

start). An internal switch discharges this capacitor every time the chip turns

off (Vcc < UVLO, LINE < 1.24 V or > 6 V, DIS > 1.85 V, ISEN > 1.5 V,

DELAY > 2 V) to make sure it is soft-started next, and when the voltage on

the current sense pin (ISEN) exceeds 0.8 V, as long as it stays above 0.75

2DELAY

Delayed shutdown upon overcurrent. A capacitor and a resistor are

connected from this pin to GND to set the maximum duration of an

overcurrent condition before the IC stops switching and the delay after

which the IC restarts switching. Every time the voltage on the ISEN pin

exceeds 0.8 V, the capacitor is charged by an internal 150 µA current

generator and is slowly discharged by the external resistor. If the voltage

on the pin reaches 2 V, the soft-start capacitor is completely discharged so

that the switching frequency is pushed to its maximum value and the 150

µA is kept always on. As the voltage on the pin exceeds 3.5 V the IC stops

switching and the internal generator is turned off, so that the voltage on the

pin decays because of the external resistor. The IC is soft-restarted as the

voltage drops below 0.3 V. In this way, under short-circuit conditions, the

converter works intermittently with very low input average power.

3CF

Timing capacitor. A capacitor connected from this pin to GND is charged

and discharged by internal current generators programmed by the external

network connected to pin 4 (RFmin) and determines the switching

frequency of the converter.

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