IR3721 datasheet(5/16 Pages) IRF

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IR3721

DATA SHEET

Page 5 of 16

www.irf.com

09/15/08

FUNCTIONAL DESCRIPTION

Please refer to the Functional Description Diagram

below. Power flow from the buck converter inductor is

the product of output voltage times the current IL

flowing through the inductor.

Power is measured with the aid of International

Rectifier’s proprietary TruePower™ circuit. Current is

converted to a duty ratio that appears at the DI pin.

The duty ratio of the DI pin is

⋅

)

(

⋅

RATIO

DUTY

DCR

Equation 1

The full-scale current that can be measured

corresponds to a duty ratio of one.

The amplitude of the DI pin is the voltage appearing

at pin VK. If a fixed voltage is applied to VK then the

output of the RC filter driven by DI will be proportional

to inductor current IL.

If VO is applied to VK as shown in the figure then the

output of the DI driven RC network will be

proportional to power. The full-scale voltage that can

be measured is established on the chip to be 1.8V.

The full scale power PFS that can be measured is the

product of full-scale voltage and full scale current.

RCS2

GND

CCS2

Power

RCS1

CCS1

DCR

VRT

VDD

IR3721

VCS

Vin

Figure 1 Functional Description Diagram

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