L6699D datasheet(6/38 Pages) STMICROELECTRONICS

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Pin connections

L6699

6/38

Doc ID 022835 Rev 2

Pin connections

Figure 2.

Pin connections (top view)

Table 4.

Pin functions

Name

Function

CSS

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

RFmin (pin 4) that set both the initial 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 < 1.25 V, DIS > 1.85 V, ISEN > 1.5 V, DELAY > 2 V) to make sure it is soft-

started next. Additionally the switch is activated when the voltage on the current

sense pin (ISEN) exceeds 0.8 V or when the converter is working too close to,

or in, the capacitive-mode operation.

2DELAY

Delayed shutdown upon overcurrent. A capacitor and a resistor are connected

from this pin to GND to set both 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 350 µA current pulses and is slowly discharged by the external

resistor. If the voltage on the DELAY pin reaches 2 V, the soft-start capacitor is

completely discharged so that the switching frequency is pushed to its

maximum value and the 350 µA current source is kept always on. As the

voltage on the DELAY 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.

If the voltage on the ISEN pin exceeds 1.5 V, the L6699 is immediately stopped

and the 350 µA current source is kept on until the voltage on the DELAY pin

reaches 3.5 V. Then, the generator is turned off and the voltage on the pin

decays because of the external resistor. Also in this case the IC is soft-restarted

as the voltage drops below 0.3 V.

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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