L6711 datasheet(25/50 Pages) STMICROELECTRONICS

25 / 50 page

L6711

Voltage positioning

25/50

Since IDROOP depends on the current information about the three phases, the output

characteristic vs. load current is given by:

Where RSENSE is the chosen sensing element resistance (Inductor DCR or LS RdsON), IOUT

is the output current of the system and RDROOP is its equivalent output resistance (The

whole power supply can be then represented by a "real" voltage generator with a voltage

value of VID and an equivalent series resistance RDROOP).

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

Figure 10.

Voltage positioning with offset

10.2

Offset

The OFFSET pin allows programming a positive or a negative offset (VOS) for the output

voltage.

When the Integrated Thermal Sensor is disabled (TC = SGND) a resistor ROFFSET

connected vs. SGND increases the output voltage: since the pin is internally fixed at 1.240V,

the current programmed by the resistor ROFFSET is mirrored and then properly subtracted

from the IFB current (see Figure 10) as follow (Only the IOFFSET contribute to IFB has been

considered):

The device will add the programmed offset VOS to the output programmed voltage

(considering now also the droop effect) subtracting the relative offset current from the

feedback current IFB:

VID

DR OOP

⋅

–

VID

SENSE

--------------------- IOUT

⋅⋅

–

VID

DROOP

OUT

⋅

–

DROOP

SEN SE

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

⋅

1.240V

1:1

ROFFSET

OFFSET

IDROOP

VID

COMP

VSEN

64k

FBR

FBG

64k

RFB

To Vcore

(Remote Sense)

IOFFSET

OUT

VID

OFFSET

⋅

VID

1.240V

OFFSET

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

⎝⎠

⎛⎞

⋅

VID

⋅

–

VID

D ROOP

OFFSET

–

() = VID R

OFFSET

D ROOP IOUT

⋅

–

⋅

–

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