Application information

HVLED001B

20/33

DS12748 Rev 2

7.1.2

Ramp-up mode

This is a particular operational mode, identical to active mode, where timed protections

(Brownout and Over Power Protection - see relevant graphs) are ignored. This mode ends

after a fixed period (Tss) since the first crossing upwards of VCC voltage. After Tss, the IC

enters active mode.

7.1.3

Active mode

This is the normal operational mode. During this state the external MOSFET is driven

according to signals coming from the application in order to regulate the desired output

parameter in closed loop (peak current control method).

Active mode is exited when abnormal conditions are present or VCC drops below the

VCC,su threshold. The HVSU is inactive during active mode.

7.1.4

Low consumption mode

This state is intended to stop the switching activity reducing the power consumption to a

minimum level.

During this state the VCC is kept between VCC,su and VCC,on by the high voltage startup

unit (HVSU) delivering Icharge to the output capacitor.

7.1.5

Stop mode

This state is intended to stop the switching activity without turning off the entire function set,

to quickly restart when abnormal or disabling conditions end. During this state the power

consumption is not minimized and the HVSU is not enabled. In case the OPTO pin drops

below the disabling threshold or VCC voltage drops below the VCC,su voltage and the IC

state evolves into low consumption state.

Note:

IMPORTANT: HVSU charges VCC so any other external voltage (including auxiliary

winding) must be de-coupled using a Diode (e.g. 1N4148).

7.2

Control loop

The control loop is based on the current mode Quasi Resonant flyback control scheme and

is therefore performed turning off the MOSFET when the peak of its source current reaches

the threshold set by the control loop, and turning the MOSFET on in correspondence with

the resonant valley following the primary side demagnetization input.

A detail of the block involved in this scheme is shown in Figure 20.