Functional check

AN3105

14/30

Doc ID 16774 Rev 2

Figure 10.

EVL130W-SL-EU demonstration board: output voltage variation driving

a CC LED converter - PWM = 90% and PWM = 15%

It is worth clarifying that, for correct operation with LED strips, the board needs some

additional capacitors connected on the +48 V output bus. It has not been equipped with all

the capacitors necessary for correct operation with LEDs but only with minimum

capacitance to allow board operation, in order to optimize the system cost and reliability.

The additional capacitors needed are intended to be placed close to each LED strip current

regulator, therefore filtering the EMI generated by these. In several cases, in fact, the power

supply is placed at the base of the lighting pole while the LED current regulators are located

on top, in the lamp. The long wiring connection between the power supply and the

converters can act as an antenna radiating EMI. Therefore local filtering minimizes the

radiated EMI.

The capacitance to be added to the 48 V bus, for correct operation with LEDs, is around

40 µF. In order to not affect the board MTBF, using the same capacitor type already used on

the power supply board is suggested.

4.4

Overcurrent and overvoltage protection

The L6599AT is equipped with a current sensing input (pin #6, ISEN) and a dedicated

overcurrent management system. The current flowing in the resonant tank is detected and

the signal is fed into the ISEN pin. It is internally connected to a first comparator, referenced

to 0.8 V, and to a second comparator referenced to 1.5 V. If the voltage externally applied to

the pin exceeds 0.8 V, the first comparator is tripped causing an internal switch to be turned

on and discharging the soft-start capacitor C24 (CSS). Under output short-circuit, this

operation results in a nearly constant peak primary current.

With the L6599AT the designer can program externally the maximum time that the converter

is allowed to run overloaded or under short-circuit conditions. Overloads or short-circuits

lasting less than the set time do not cause any other action, and so provide the system with

immunity to short duration phenomena. If, instead, an overload condition continues,

a protection procedure is activated which shuts down the L6599AT. In the case of

continuous overload or short-circuit, it results in continuous intermittent operation with

a user defined duty cycle.

CH1: PWM dimming signal

CH1: PWM dimming signal

CH4: SMPS output current

CH4: SMPS output current