L6718 datasheet(56/71 Pages) STMICROELECTRONICS

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Output voltage monitoring and protection

L6718

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DocID023399 Rev 3

possible undershoot. To reach this target, a special sequence is performed, as per the

following:

–

The device turns on all low-side MOSFETs (and keeps to GND the PWMx) of the

section where OV protection is triggered. At the same time the device performs a

fast DVID moving the internal reference to 250 mV.

–

The section which triggered the protection switches between all MOSFETs OFF

and all low-sides ON in order to follow the voltage imposed by the DVID_Fast on-

going. This limits the output voltage excursion, protects the load and assures no

undershoot is generated (if VOUT < 250 mV, the section is HiZ).

–

The non-involved section turns off all the MOSFETs in order to realize a HiZ

condition. Only if the non-involved section runs in Jmode does the rail keep

switching.

–

xOSC/ FLT pin of the OVP involved section is driven high.

If the cause of the failure is removed, the converter ends the transition with all PWMs in HiZ

state and the output voltage of the section which triggered the protection lower than 250 mV.

The enable or VCC cycle (VCC5 or VCC12) can restart the system but the enable cycle

does not discharge the SMBus embedded register, in this case, a VCC cycle is necessary to

restart the system with default value.

9.2

Overcurrent

The overcurrent threshold can be programmed to a safe value to avoid the system not

entering OC during normal operation of the device. This value must take 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). Two OCP types (for

average and for phase) can be detected on each rail.

9.2.1

Multi-phase section

The L6718 performs two different OC protections for the multi-phase section: it monitors

both the total current and the per-phase current and allows the setting of an OC threshold

for both.

–

Phase OC. Maximum information current phase (IINFOx) is internally limited to 35

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). Skipping

cycle, latch condition occurs when UVP is reached.

–

Total current OC. The IMON pin allows a maximum total output current for the

system (IOC_TOT) to be defined. The total sum IMON of the current read on each

phase (IINFOx) is sourced from the IMON pin. By connecting a resistor RIMON to

SGND, a load indicator with VOC_TOT end-of-scale can be implemented. When the

voltage present at the IMON pin crosses VOC_TOT, the device detects an OC and

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

can be selected through SMbus dynamically or using CONFIG2 as pinstrapping. It

is possible to choose:

OCP=125% of IMAX, so VOC_TOT =1.55 V

OCP=137% of IMAX, so VOC_TOT =1.7 V (default)

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