IR3721 datasheet(7/16 Pages) IRF

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IR3721

DATA SHEET

Page 7 of 16

www.irf.com

09/15/08

TYPICAL 2-PHASE DCR SENSING APPLICATION

The IR3721 is capable of monitoring power in a

multiphase converter. A Two Phase DCR Sensing

Circuit is shown below. The voltage output of any

phase is equal to that of any and every other phase

because they are electrically connected and

monitored at VO as before.

Output current is the sum of the two inductor currents

(IL1 + IL2). Superposition is used to derive the transfer

function for multiphase sensing. The voltage on RCS2

due to IL1 is

)

(

)

(

⋅

DCR

Likewise, the voltage on RCS2 due to IL2 is

)

(

)

(

⋅

DCR

The current through RCS2 due to both inductor

currents is ICS. From the two equations above

DCR

The duty ratio of DI is

REF

DUTYRATIO

⋅

If DCR1=DCR2, and RCS1=RCS3, then ICS can be

simplified to

2 CS

DCR

⋅

)

(

and the DI duty ratio simplifies to

⋅

)

(

⋅

)

(

DUTYRATIO

DCR

Full scale current occurs when DI duty ratio becomes

one.

Figure 3 Two Phase DCR Sensing Circuit

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