L6599A
Pin connection
3
Pin connection
Figure 2.
Pin connection (top view)
Table 2.
Pin N#
Pin description
Type
Function
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
V.
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.
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.
1
Css
2
DELAY
3
CF
Doc ID 15308 Rev 7
5/35
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