IR3521 datasheet(30/45 Pages) IRF

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IR3521

Page 30

V3.03

NLOFST



(12)

Adaptive voltage positioning lowers the converter voltage by RO*IO, where RO is the required output impedance of

the converter. Pre-select feedback resistor RFB, and calculate the droop resistor RDRP,

ROOM

DRP





(13)

Calculate the desired effective feedback resistor at the maximum temperature RFB_M using (14)

MAX

DRP





(14)

A negative temperature constant (NTC) thermistor RTHERM1 is required to sense the temperature of the power stage

for the inductor DCR thermal compensation. Pre-select the value of RTHERM. RTHERM must be bigger than RFB_R at

room temperature but also bigger than RFB_M at the maximum allowed temperature. RTMAX1 is defined as the NTC

thermistor resistance at maximum allowed temperature, TMAX. RTMAX1 is calculated from (15).

)]

(

[

ROOM

MAX

THERM

TMAX

EXP





(15)

Select the series resistor RFB13 by using equation (16). RFB13 is incorporated to linearize the NTC thermistor which

has non-linear characteristics in the operational temperature range.

)

(

))

)

(

)

(

TMAX

THERM

TMAX

THERM

TMAX

THERM

TMAX

THERM









(16)

Use equation (17) to determine RFB11.

THERM







(17)

IR3521 Datasheet(PDF) 30 Page - International Rectifier

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