L6572

Functional description

Doc ID 023882 Rev 1

11/22

The internal information cell is provided with the structure embedded in TSD pin and is able

to keep its state as long as the voltage on this pin is above VTSD. When the voltage on the

TSD pin decreases below VTSD before the ballast is reconnected to the mains, the

information cell is set to a state that leads to nominal light output of the lamp when the lamp

is reconnected to the line voltage next time.

The time tTSD is defined by the voltage of the half-bridge when the oscillation stops, the

current consumption (ITSD) of the TSD-pin and the resistor RA. Decreasing the time, tTSD

may be achieved by connecting a resistor RB between the TSD pin and GND. (see

Figure 7).

When the lamp is operated with reduced light output, the thermal powerboost time (see

Section 5.6) is shortened to 1022 period times of the clock generator in any case.

If the voltage on the TSD pin is kept below 0.5 V until the lamp has ignited, a change

between normal operation mode and dimmed operation mode can be achieved by every

transition of the voltage on the TSD pin while the lamp is burning: a voltage VTSD < 0.5 V

leads to the normal operation, a voltage VTSD > 6.2 V (typ.) leads to the dimmed operation.

Steady-state voltages between 0.5 V and 6.2 V (typ.) on the TSD pin have to be avoided.

The current consumption of the TSD pin is controlled by design with an internal bias circuit

that has a compensated temperature behavior.

The two-step dimming function can be deactivated by connecting the TSD pin to GND. In

this case, the lamp is always operated with nominal light output.

5.5

Rated current generation

A reference current is used to feed the external resistors RPH, RNO and RDO. The voltages

formed across these resistors are converted into internal rated voltage for integrator's

comparator during each operation phases of the ballast (see Figure 5).

In order to compensate both the tolerances and the temperature variations of such a

reference current, it is matched with the current used to charge the integrating capacitance

Cint. As a result, the obtained lamp current has the same tolerance as the external

programming resistors even if the relevant rated voltages have noticeable variations.

During the preheating phase, the rated resonant current is defined by the external resistor

RPH.

The length of the preheating phase is defined by the duration of 40960 period times of the

clock generator (a frequency fCL=100 kHz results in a duration of the preheating phase of

410 ms).

During the ignition phase, the rated resonant current increases from the preheating level to

a level that ensures an operation of the half-bridge very close to the pole frequency of the

resonant lamp circuit.

This increase is internally reached with a ramp composed by 31 steps given by the D/A-

converter block. In the first half of the ramp, height out of the ramp steps are smaller than

those in the second half of the ramp. The length of each step is defined by the duration of

512 half waves of the resonant current. The last step of the ramp is reached after 15872 half

waves (512 x 31).

The end of the ignition phase is reached only when the ignition recognition unit delivers a

trigger signal (Section 5.11). In this case, the ignition phase is ended and the rated resonant