DS12748 Rev 2

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HVLED001B

Application information

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7.4.2

High voltage startup

High voltage startup (HVSU) circuitry is primarily intended to provide the start-up current to

the VCC pin and maintain the IC responsive during low consumption modes.

This structure is able to sustain at least 800 V to avoid any damage in case of a surge or

burst on the stage's input.

The overall structure is OFF until input voltage reaches VHVSU,start threshold; after that it

sources a minimum current (Icharge,su) to charge the VCC pin up to Vcc,su threshold. This

condition prevents the IC from severe damage in the case of short-circuit on the VCC pin.

At this VCC voltage a higher current (Icharge) is provided to VCC to reach the VCC,on

threshold. On this occurrence the ramp-up mode is invoked and the HVSU is turned off.

During other active mode phases and stop mode the HVSU is OFF.

If low consumption mode is entered, the HVSU unit is turned on.

Table 7 summarizes the HVSU behavior in all IC conditions.

7.5

Auto restart timer (ART)

The Auto Restart Timer unit is responsible for the generation of the protection's intervals

and of the restart times after low consumption mode. A summary of all possible

combinations of times is described in each protection section.

Table 7. HVSU operating modes

Operating condition

VCC range

OFF Icharge,su Icharge

All states if VIN < VHVSU,ON

X

-

-

Startup (logic startup)

0 V … Vcc,su

-

X

-

Startup (IC startup)

Vcc,su … Vcc,on

-

-

X

Active mode and Ramp-up mode

Vcc,su … VCC,MAX

X

-

-

Stop mode

Vcc,su … VCC,MAX

X

-

-

Low consumption mode

Vcc,su

-

-

X

Low consumption mode

(after the end of entering conditions)

Vcc,su … Vcc,on

-

-

X