Once the protection set-up is fetched, the following pins are pulled up: FB, VL, FAULT and OPTO.

When the voltage on the FAULT pin is higher than VFLT-ON threshold, the HVSU recharges the VCC capacitor and

the switching activity starts. The first switching cycles activate the next operating phase: the ramp-up phase.

6.2.2

Ramp-up phase

This operating mode is intended to ensure a safe increase of the output voltage. This goal is achieved transferring

an almost constant power to the output by fixing the minimum current sense threshold at VCS-RU and driving the

external power MOSFET at constant operating frequency FSW-RU, with the maximum duty cycle fixed at 50%.

The THD optimizer unit is forced to operate with a duty cycle equal to 1 (see relevant section for further details).

Figure 6. Ramp-up waveforms

Max duty fixed by

CK falling edge

VGD

VCS-RU

VCS

FSW-RU

When both output voltages (read by ZCD sample and hold block) are higher than VUVP threshold and OPTO pin is

pulled up for at least TOPTO-TRIG, the IC enters active mode.

If the ramp-up exit condition is not satisfied within TCF, the IC shuts down, and automatic restart is attempted after

TART.

During this phase the internal PSR error amplifier is always on as well as the FAULT pin pull-up current.

6.2.3

Active mode

During active mode, the IC provides the GD signal to drive the external power switch according to application

signals.

All the parameters are set at their operating range performance and protections are ready to manage undesired

events.

The power consumption of the IC in this phase depends on the switching frequency and the characteristics of the

adopted switch.

The OPTO disable feature activates a deep low consumption mode, while the FAULT disable mean activates a

standard low consumption mode.

The input OVP is active (in CFG 1, 3 and 5) as well as the brownout and output undervoltage protections.

6.2.4

Low consumption mode

In this state, the IC stops switching activity and turns off the major part of internal structures in order to reduce

VCC consumption down to ICC-LC.

In this operating mode, the high-voltage startup logic is active to maintain the VCC pin above VCC-OFF (low level)

if necessary.

This state is invoked when the following conditions are met:

•

overcurrent protection.

•

FAULT pin protection.

•

the inactive phase of brownout level protection is running.

•

input overvoltage protection senses an excessive input voltage at pin HVSU.

HVLED101

Operating modes

DS14143 - Rev 2

page 14/36