L6706 datasheet(36/47 Pages) STMICROELECTRONICS

36 / 47 page

Output voltage monitor and protections

L6706

36/47

Doc ID 15698 Rev 2

OCP during normal operation of the device. This value must take into consideration also the

extra current needed during the dynamic VID transition ID-VID (see Section 12: Dynamic VID

transitions for details):

The device detects an over current when the IINFO overcome the threshold IOCTH externally

programmable through OCSET pin.

where

ΔIL is the inductor ripple current (peak-to-peak).

Since the device always senses the current across the inductor, the IOCTH crossing will

happen during the HS conduction time: as a consequence of OCP detection, the device will

turn OFF the HS MOSFET and turns ON the LSMOSFET until IINFO re-cross the threshold

or until the next clock cycle. This implies that the device limits the peak of the inductor

current.

In any case, the inductor current won't overcome the IOCP value and this will represent the

maximum peak value to consider in the OC design.

The device works in constant-current, and the output voltage decreases as the load

increase, until the output voltage reaches the UVP threshold. When this threshold is

crossed, MOSFETs are turned off and the device stops working. Cycle the power supply or

the OUTEN pin to restart operation.

Figure 20.

Overcurrent protection connection

Note:

In order to avoid the OCP intervention during the DVID, the device automatically increases

the OCP threshold to 150% of the selected OCP threshold during every VID transition

(adding an extra 15 µs of delay).

Since the device reads the current information across inductor DCR, the process spread

and temperature variations of these sensing elements has to be considered. Also the

programmable threshold spread (IOCTH current spread as a consequence of VOCSET

spread, see Table 5) has to be considered for the ROCSET design:

IOUT

OCP

IOUT

MAX

DVID

–

OCTH

OCSET

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

1.260 typ

()

OCSET

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

INFO

OCP

DCR

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

OUT

OCP

ΔIL

---------

⎝⎠

⎛⎞

⋅

ROCSET

OCSET

VOCSET =1.260V (TYP)

OCSET

OCSET MIN

()

DCR MAX

)

()

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

OUT OCP

() ΔIL

---------

⎝⎠

⎛⎞

⋅

μA

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

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