DocID027333 Rev 1

19/27

HVLED001

Application information

27

The TOFF pin is intended to select the blanking time duration. If the pin is left unconnected

a fixed blanking time is provided.

The TBLANK value depends on Toff voltage (Figure 9).

Figure 9. TBLANK voltage vs Tblank time (typical)

An internal starter provides the triggering signal whenever a valid arming signal is not

detected.

The ZCD pin embeds a negative clamp to limit the negative-going current.

7.2.4

Primary side regulation feature

The ZCD pin is also is used as input of the PSR error amplifier (E/A). The reference voltage

of this loop is internally fixed to VREF,PSR and applied to the non-inverting input of the E/A.

The output of such error amplifier is connected to the FB pin where the relevant

compensation network has to be connected.

In a flyback or buck-boost topology the output voltage can be read from the primary side

using an auxiliary winding: in this case the output voltage is obtained using the following

equation:

Equation 3

Vout

VREF PSR

--------------

1

Rzcd

Rfb

--------------

+











=