L6759D datasheet(29/51 Pages) STMICROELECTRONICS

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L6759D

Output voltage monitoring and protection

Doc ID 023240 Rev 1

29/51

into consideration also the extra current needed during the DVID transition (IDVID) and the

process spread and temperature variations of the sensing elements (inductor DCR).

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

mum/maximum values of the threshold.

7.2.1

Multi-phase section

The L6759D features two independent load indicator signals, IMON and ILIM, to properly

manage OC protection, current monitoring and DPM. Both IMON and ILIM sources a current

proportional to the current delivered by the regulator, as follows:

Equation 12

The IMON and ILIM pins are connected to GND through a resistor (RIMON and RILIM respec-

tively), implementing a load indicator with different targets.

●

IMON is used for current reporting purposes and for the DPM phase shedding. RIMON

must be designed considering that IMAX must correspond to 1.24 V (for correct IMAX

detection)

●

ILIM is used for the overcurrent protection only. RILIM must be designed considering that

the OC protection is triggered when V(ILIM)=2.5 V.

In addition, the L6759D also performs per-phase OC protection.

●

Per-phase OC. Maximum information current per-phase (IINFOx) is internally limited to

µA. This end-of-scale current (IOC_TH) is compared with the information current

generated for each phase (IINFOx). If the current information for the single-phase

exceeds the end-of-scale current (i.e. if IINFOx > IOC_TH), the device turns on the LS

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

●

Total current OC. The ILIM pin allows a maximum total output current to be defined for

the system (IOC_TOT). The ILIM current is sourced from the ILIM pin. By connecting a

resistor RILIM to GND, a load indicator with 2.5 V (VOC_TOT) end-of-scale can be

implemented. When the voltage present at the ILIM pin crosses VOC_TOT, the device

detects an OC and immediately latches with all the MOSFETs of all the sections OFF

(HiZ).

The typical design considers the intervention of the total current OC before the per-phase

OC, leaving this last one as an extreme-protection in case of hardware failures in the exter-

nal components. Per-phase OC depends on the RG design while total OC is dependant on

the ILIM design and on the application TDC and max. current supported. The typical design

flow is the following:

●

Define the maximum total output current (IOC_TOT) according to system requirements

(IMAX, ITDC). Considering the IMON design, IMAX must correspond to 1.24 V (for correct

IMAX detection) while in the ILIM design, IOC_TOT must correspond to 2.5 V

●

Design the per-phase OC and RG resistor in order to have IINFOx = IOC_TH (35 µA)

when IOUT is about 10% higher than the IOC_TOT current. It results:

MON

LIM

DCR

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

OUT

⋅

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