IR3721 International Rectifier, IR3721 Datasheet - Page 7

• Manufacturer Part Number: IR3721
• Description: Power Monitor IC
• Manufacturer: International Rectifier

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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
(I
function for multiphase sensing. The voltage on R
due to I
Likewise, the voltage on RCS2 due to IL2 is
The current through R
currents is I
Page 7 of 16
L1
+ I
L2
I
L1
). Superposition is used to derive the transfer
CS
is
I
I
=
L
L
CS
2
1
R
⋅
⋅
. From the two equations above
DCR
CS
DCR
I
L
1
1
R
DCR
CS
1
2
⋅
⋅
2
R
CS2
R
1
+
R
CS
CS
R
CS
(
due to both inductor
1
(
CS
R
3
R
3
+
CS
+
1
CS
+
(
R
R
(
2
I
R
CS
2
L
CS
||
2
CS
||
DCR
3
R
R
2
2
+
CS
CS
||
||
R
R
3
Figure 3 Two Phase DCR Sensing Circuit
R
1
CS
2
CS
)
)
R
CS
2
3
CS
R
1
)
)
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1
CS
3
CS2
The duty ratio of DI is
If DCR1=DCR2, and RCS1=RCS3, then I
simplified to
and the DI duty ratio simplifies to
Full scale current occurs when DI duty ratio becomes
one.
DI
DUTYRATIO
I
DI
CS
DUTYRATIO
=
(
=
I
L
R
1
(
(
CS
R
I
+
L
CS
1
1
I
L
+
=
+
1
2
I
⋅ )
2
+
L
I
CS
2
R
V
2
DCR
⋅ )
R
REF
CS
⋅
DCR
CS
R
2
T
DATA SHEET
1
2
⋅ )
IR3721
⋅
V
R
07/14/08
CS
R
T
Τ
can be