L6599AD datasheet(27/35 Pages) STMICROELECTRONICS

27 / 35 page

L6599A

Application information

Doc ID 15308 Rev 7

27/35

Figure 30.

Line sensing function: internal block diagram and timing diagram

With reference to

Figure 28, the following relationships can be established for the ON

(VinON) and OFF (VinOFF) thresholds of the input voltage:

Equation 11

which, solved for RH and RL, yields:

Equation 12

While the line undervoltage is active, the startup generator keeps on working but there is no

PWM activity, therefore the Vcc voltage (if not supplied by another source) continuously

oscillates between the startup and the UVLO thresholds, as shown in the timing diagram of

Figure 30.

As an additional safety measure (e.g. in case the low-side resistor is open or missing, or in

non-power factor corrected systems in case of abnormally high input voltage), if the voltage

on the pin exceeds 7 V, the L6599A is shut down. If its supply voltage is always above the

UVLO threshold, the IC restarts as the voltage falls below 7 V.

The LINE pin, while the device is operating, is a high impedance input connected to high

value resistors, therefore it is prone to pick-up noise, which might alter the OFF threshold or

give origin to undesired switch-off of the IC during ESD tests. It is possible to bypass the pin

to ground with a small film capacitor (e.g. 1-10 nF) to prevent any malfunctioning of this kind.

OFF

Vin

−

⋅

−

Vin

;

Vin

OFF

−

⋅

−

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