L6699
Pin connections
Table 4.
N.
Pin functions (continued)
Name
Function
Minimum oscillator frequency setting. This pin provides an accurate 2 V
reference, and a resistor connected from this pin to GND defines a current that
is used to set the minimum oscillator frequency. To close the feedback loop that
regulates the converter output voltage by modulating the oscillator frequency,
the phototransistor of an optocoupler is connected to this pin through a resistor.
The value of this resistor sets the maximum operating frequency. Initial
operating frequency should be set below 300 kHz; it is recommended not to
exceed such limit. An R-C series connected from this pin to GND sets
frequency shift at startup to prevent excessive energy inrush (soft-start).
4
RFmin
Burst-mode operation threshold. The pin senses some voltage related to the
feedback control, which is compared to an internal reference (1.26 V). If the
voltage on the pin is lower than the reference, the IC enters an idle state and its
quiescent current is reduced. The chip restarts switching as the voltage
exceeds the reference by 30 mV. Soft-start is not invoked. This function realizes
burst-mode operation when the load falls below a level that can be programmed
by properly choosing the resistor connecting the optocoupler to the RFmin pin
(see Figure 1: Block diagram). Tie the pin to RFmin if burst-mode is not used.
5
STBY
Current sense input. The pin senses the instantaneous primary current though
a sense resistor or a capacitive divider for lossless sensing. If the voltage
exceeds a 0.8 V threshold the soft-start capacitor connected to pin 1 is
internally discharged: the frequency increases and so limits the power
throughput. Under output short-circuit, this normally results in a nearly constant
peak primary current. This condition is allowed for a maximum time set at pin 2.
If the current keeps on building up despite this frequency increase, a second
comparator referenced to 1.5 V disables switching immediately and activates a
restart delay procedure (see DELAY pin description for more information).
6
ISEN
This pin is used also for capacitive-mode operation detection and for hard-
switching prevention at startup. Do not short the pin to ground; this would
prevent the device from operating correctly.
Line sensing input. The pin is to be connected to the high voltage input bus with
a resistor divider to perform either AC or DC (in systems with PFC) brownout
protection. A voltage below 1.25 V shuts down the IC, lowers its consumption
and discharges the soft-start capacitor. IC operation is enabled as the voltage
exceeds 1.25 V. The comparator is provided with current hysteresis: an internal
13 µA current generator is ON as long as the voltage applied at the pin is below
1.25 V, and is OFF if this value is exceeded. Bypass the pin with a capacitor to
GND to reduce noise pick-up. The voltage on the pin is top-limited by an
internal Zener. Tie the pin to VCC with a =100 kΩ resistor if not used.
7
8
LINE
Latched device shutdown. Internally, the pin connects a comparator that, when
the voltage on the pin exceeds 1.85 V, shuts the IC down and brings its
consumption almost to a “before startup” level. The information is latched and it
is necessary to recycle the supply voltage of the IC to enable it to restart: the
latch is removed as the voltage on the VCC pin goes below the UVLO threshold.
Tie the pin to GND if the function is not used.
DIS
Open-drain ON/OFF control of PFC controller. This pin, normally open, is
intended for stopping the PFC controller, for protection purposes or during
burst-mode operation. It goes low when the IC is shut down by DIS > 1.85 V,
9
PFC_STOP ISEN > 1.5 V and STBY < 1.25 V. The pin is pulled low also when capacitive
mode operation is detected and when the voltage on the DELAY pin exceeds 2
V. In this latter case it goes back open as the voltage falls below 0.3 V. During
UVLO, it is open. Leave the pin unconnected if not used.
Doc ID 022835 Rev 2
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