L6711 datasheet(26/50 Pages) STMICROELECTRONICS

26 / 50 page

Voltage positioning

L6711

26/50

Offset resistor can be designed by considering the following relationship (RFB is fixed by the

Droop effect):

Offset automatically given by the DAC selection or by VID5 when VID_SEL=SGND differs

from the offset implemented through the OFFSET pin: the built-in feature is trimmed in

production and assures ±0.5% error (±0.6% for the Hammer DAC) over load and line

variations while implementing the same offset through the OFFSET pin causes additional

errors to be considered in the total output voltage precision.

When the Integrated Thermal Sensor is enabled (see Figure 11 and following section), the

pin programs, in the same way as before, a negative offset. This is to compensate the

positive native offset introduced by the ITS. The effect of the programmed offset on the

output voltage results (IOFFSET is now added to IFB and no more subtracted as before):

Offset resistor is designed to compensate the ITS native offset as described in the following

section.

The Offset function can be disabled by shorting the pin to SGND.

Figure 11.

Voltage positioning with integrated thermal sensor

10.3

Integrated thermal sensor

Current sense elements have non-negligible temperature variations: considering either

inductor or LS mosfet sense, the sensing elements modify proportionally to varying

temperature. As a consequence, the sensed current is subjected to a measurement error

that causes the regulated voltage to vary accordingly.

To recover from this temperature related error, a temperature compensation circuit is

integrated into the controller: the internal temperature is sensed and the droop current is

corrected (according to a scaling external resistor RTC) in order to keep constant the

regulated voltage.

OFFSET

1.240V

------------------- RFB

⋅

OUT

VID

OFFSET

⋅

–

VID

1.240

OFFSET

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

⎝⎠

⎛⎞

⋅

–

VID

–

1.240V

1:1

VTC=A+B·(TJ-25)

RTC

ROFFSET

OFFSET

1:1

IDROOP

VID

COMP

VSEN

64k

FBR

FBG

64k

RFB

To Vcore

(Remote Sense)

IOFFSET

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