L6713A datasheet(49/64 Pages) STMICROELECTRONICS

49 / 64 page

L6713A

Over current protection

49/64

Over current protection

The device limits the total delivered current turning OFF all the MOSFETs as soon as the

delivery current is higher than an adjustable thresholds.This condition is lathed and power

supply or OUTEN pin cycling is required to restart operations.

The device sources a copy of IDROOP current from the OCSET pin: connecting a resistor

ROCP between OCSET pin and SGND the voltage at the OCSET pin depends on the total

delivery output current, as shown in the following relationships:

Figure 23.

OCP connections (left) and waveforms (right)

As soon as the OCSET pin voltage is higher than the internal fixed thresholds VOCTH (1.24 V

TYP, See Table 5), the device turns OFF all the MOSFETs and latches the condition.

The OCP threshold can be easily programmed through the ROCP resistor:

The output over current threshold has to be programmed, by designing the ROCP resistors,

to a safe value, in order to be sure that the device doesn't enter 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 and, since the device reads across inductor

DCR, the process spread and temperature variations of these sensing elements.

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

minimum value VOCTH(min) of the threshold as follow:

where IOUT(OCP) is the total delivery current for the over current condition and it must be

calculated considering the maximum delivery current and ID-VID (when D-VID are

implemented):

When it is necessary, filter OCSET pin to introduce a small delay in the over current

intervention.

OCSET

OCP

DROOP

⋅

OCP

DCR

------------- I

OUT

⋅⋅

OCP

COMPARATOR

DROOP

ROCP

OCSET

COCP

VOCTH=1.240V

UGATE

LGATE

OCSET

VOUT

OCP

DCR

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

OCTH

OUT OCP

()

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

⋅

OCP

DCR max

()

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

OCTH min

()

OUT OCP

()

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

⋅

OUT OCP

()

OUT

MAX

DVID

–

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