L6713ATR datasheet(36/64 Pages) STMICROELECTRONICS

36 / 64 page

Voltage positioning

L6713A

36/64

12.2

Droop function (Optional)

This method "recovers" part of the drop due to the output capacitor ESR in the load

transient, introducing a dependence of the output voltage on the load current: a static error

proportional to the output current causes the output voltage to vary according to the sensed

current.

As shown in Figure 11, the ESR drop is present in any case, but using the droop function

the total deviation of the output voltage is minimized. Moreover, more and more high-

performance CPUs require precise load-line regulation to perform in the proper way.

DROOP function is not then required only to optimize the output filter, but also beacomes a

requirement of the load.

Connecting DROOP pin and FB pin together, the device forces a current IDROOP,

proportional to the read current, into the feedback resistor (RFB+ROFFSET) implementing the

load regulation dependence. Since IDROOP depends on the current information about the N

phases, the output characteristic vs. load current is then given by (neglecting the OFFSET

voltage term):

Where DCR is the inductor parasite resistance (or sense resistor when used) and IOUT is the

output current of the system. The whole power supply can be then represented by a "real"

voltage generator with an equivalent output resistance RDROOP and a voltage value of VREF.

RFB resistor can be also designed according to the RDROOP specifications as follow:

Droop function is optional, in case it is not desired, the DROOP pin can be disconnected

from the FB and an information about the total delivered current becomes available for

debugging, and/or current monitoring. When not used, the pin can be shorted to SGND.

OUT

REF

OFFSET

() I

DROOP

⋅

–

REF

OFFSET

() DCR

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

OUT

⋅⋅

–

REF

DROOP

OUT

⋅

–

DROOP

DCR

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

OFFSET

–

⋅

L6713ATR Datasheet(PDF) 36 Page - STMicroelectronics

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