L6706 datasheet(23/47 Pages) STMICROELECTRONICS

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L6706

Droop thermal compensation

Doc ID 15698 Rev 2

23/47

Droop thermal compensation

Current sense element (DCR inductor) has a non-negligible temperature variation. As a

consequence, the sensed current is subjected to a measurement error that causes the

regulated output voltage to vary accordingly (when droop function is implemented).

To recover from this temperature related error, NTC resistor can be added into feedback

compensation network, as shown in Figure 8.

The output voltage is then driven by the following relationship (neglecting the OFFSET

voltage term):

where RFB is the equivalent feedback resistor and it depends on the temperature through

NTC resistor.

Considering the relationships between IDROOP and the IOUT, the output voltage results:

where T is the temperature.

If the inductor temperature increases the DCR inductor increases and NTC resistor

decreases. As a consequence the equivalent RFB resistor decreases keeping constant the

output voltage respect to temperature variation.

NTC resistor must be placed as close as possible to the sense element (phase inductor).

Figure 8.

NTC connections for DC load line thermal compensation

OUT

PROG

DROOP

⋅

()

–

OUT

)

[]

PROG

FB T

[] DCR T

[]

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

OUT

⋅⋅

⎝⎠

⎛⎞

–

COMP

To GND_core

(Remote Sense)

ERROR AMPLIFIER

FBG

DROOP

To VCC_core

(Remote Sense)

VPROG

VREF

FBG

GND DROP

RECOVERY

RFB

NTC

RFB3

RFB2

RFB1

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