L6740LTR datasheet(33/44 Pages) STMICROELECTRONICS

33 / 44 page

L6740L

Output voltage monitoring and protections

33/44

Figure 13.

FB disconnection protection

7.3

PWRGOOD

It is an open-drain signal set free after the soft-start sequence has finished; it is the logic

AND between the internal CORE and NB PGOOD (or just the CORE PGOOD in PVI mode).

It is pulled low when the output voltage of one of the two sections drops 250mV below the

programmed voltage. It is masked during On-The-Fly VID Transitions as well as when the

CORE section is set to OFF (from SVI bus) while the NB Section is still operative.

7.4

Over-current

The Over Current threshold has to be programmed to a safe value, in order to be sure that

each Section doesn't enter OC during normal operation of the device. This value must take

into consideration also the extra current needed during the OTF-VID Transition (IOTF-VID)

and the process spread and temperature variations of the sensing elements (DCR and

RdsON).

Moreover, since also the internal threshold spreads, the design has to consider the mini-

mum/maximum values of the threshold. Considering the reading method, the two sections

will show different behaviors in OC.

7.4.1

CORE section

L6740L performs two different OC protections for the CORE Section: it monitors both the

average current and the per-phase current and allows to set an OC threshold for both.

–

OC_PHASE pin allows to define a maximum information current per-phase

(IINFOx). A ROC_TH resistor connected to SGND allows to define an end-of-scale

current (IOC_TH) that is compared with the information current generated for each

phase (IINFOx). If the current information for the single phase exceed the

programmed end-of-scale current (i.e. if IINFOx > IOC_TH), the device will turn-on

the LS mosfet until the threshold is re-crossed (i.e. until IINFOx < IOC_TH).

–

OC_AVG pin allows to define a maximum total output current for the system

(IOC_AVG). A copy of the DROOP current is sourced from the OC_AVG/LI pin. By

connecting a resistor ROC_AVG to SGND, a load indicator with 2.5V (VOC_AVGTH)

end-of-scale can be implemented. This means that when the voltage present at

the LI pin crosses VOC_AVGTH, the device detects an average OC (OC_AVG) and

immediately latches with all the mosfets of all the sections OFF (HiZ).

CORE_REFERENCE

COMP

VSEN

FBG

RFB

To VDD_CORE

(Remote Sense)

from DAC...

NB_REFERENCE

NB_FB

NB_COMP

NB_VSEN

NB_FBG

RF_NB

CF_NB

RFB_NB

To VDD_NB

(Remote Sense)

CORE SECTION - VSEN AND FBG DISCONNECTION

NB SECTION - NB_VSEN AND NB_FBR DISCONNECTION

500mV

FBG DISCONNECTED

CS1-

VSEN

DISCONNECTED

from DAC...

500mV

FBG DISCONNECTED

600mV

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