IR3082P

bF

Page 13 of 33

01/31/05

The voltage at the VDRP pin is a buffered version of the share bus and represents the sum of the DAC voltage and

the average inductor current of all the phases. The VDRP pin is connected to the FB pin through the resistor RVDRP.

Since the Error Amp will force the loop to maintain FB to be equal to the VDAC reference voltage, current will flow

into the FB pin equal to (VDRP-VDAC) / RVDRP. When the load current increases, the adaptive positioning voltage

increases accordingly. More current flows through the feedback resistor RFB, and makes the output voltage lower

proportional to the load current. The positioning voltage can be programmed by the resistor RVDRP so that the droop

impedance produces the desired converter output impedance. The offset and slope of the converter output

impedance are referenced to and therefore independent of the VDAC voltage.

VDAC

Rv drp

Rf b

ISHARE

VDAC

If b

CS+

CS-

EA

Vo

VDRP

IIN

Phase IC

VDAC

ISHARE

CS+

Phase IC

CS-

Current Sense

Amplifier

10k

VDAC

FB

Error

Amplifier

Current Sense

Amplifier

+

-

Control IC

Droop

Amplifier

10k

Figure 8 - Adaptive voltage positioning

Inductor DCR Temperature Correction

If the thermal compensation of the inductor DCR provided by the temperature dependent gain of the current sense

amplifier is not adequate, a negative temperature coefficient (NTC) thermistor can be used for additional correction.

The thermistor should be placed close to the inductor and connected in parallel with the feedback resistor as shown

in Figure 9. The resistor in series with the thermistor is used to reduce the nonlinearity of the thermistor.

Figure 9 - Temperature compensation of inductor DCR

VDAC

Rv drp

Rf b

If b

EA

VDRP

Vo

IIN

Error

Amplifier

+

-

Control IC

Droop

Amplifier

Rf b

Rt

FB