IR3720MTRPBF International Rectifier, IR3720MTRPBF Datasheet - Page 10

• Manufacturer Part Number: IR3720MTRPBF
• Description: IC POWER SUPPLY MONITOR 10-DFN
• Manufacturer: International Rectifier
• Series: TruePower™r

Specifications of IR3720MTRPBF

• Package / Case: 10-DFN
• Mounting Type: Surface Mount
• Current - Supply: 480µA
• Voltage - Supply: 3.135 V ~ 3.465 V
• Operating Temperature: 0°C ~ 125°C
• Applications: Power Supply Monitor
• Voltage - Input: -
• Input Voltage: 3.3V
• No. Of Outputs: 1
• Supply Voltage Range: 3.135V To 3.465V
• No. Of Pins: 10
• Operating Temperature Range: 0°C To +125°C
• Filter Terminals: SMD
• Input Voltage Primary Max: 3.3V
• Rohs Compliant: Yes
• Frequency: 400kHz
• Package: 10 Lead 3x3 DFN
• Vk Range: 0.5V - 1.8V
• Bias Supply Voltage: +3.3V +/-5%
• Junction Temperature: 0oC to 125oC
• Pbf: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

INDUCTOR DCR CURRENT SENSING APPLICATION
Referring to the Functional Description Diagram, it
can be seen that the shunt function can be
accomplished by the DC resistance of the inductor
that is already present. Omitting the resistive shunt
reduces BOM cost and increases efficiency. In
exchange for these two significant advantages two
easily compensated design complications are
introduced, a time constant and a temperature
coefficient.
The inductor voltage sensed between the Rcs1
resistors is not simply proportional to the inductor
current, but rather is expressed in the Laplace
equation below.
This inductor time constant is canceled when
Let
A second equation is used to set the full scale
inductor current.
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I
R
DCR
FS
CS1
V
L
L
=
R
R
+
=
V
R
CS1
=
CS1
IG
R
Ι
T
L
R
R
CS2
+
⋅
CS1
⋅
⋅
CS1
R
(
DCR
R
R
CS2
=
CS2
CS1
+
⋅
R
R
DCR
R
⎛
⎜
⎝
sum
CS2
+
1
CS2
=
+
R
R
CS2
s
and solve for Rsum.
eq
⋅
DCR
C
.
L
CS1
)
. Let
⎞
⎟
⎠
.
www.irf.com
Select a standard value C
We now know Req and Rsum, but we do not know
the individual resistor values R
step is to solve for them simultaneously. By
substituting R
can be written:
Note that this equation is of the form
c=Req•Rsum. The roots of this quadratic equation
will be R
as R
and
R
R
R
R
ax
DCR
eq
2
CS1
CS1
CS1
2
+
4
=
CS1
−
⋅
=
=
⋅
bx
R
R
L
R
R
R
CS1
SUM
in order to minimize ripple current in C
CS1
CS1
+
SUM
SUM
R
c
sum
⋅
⋅
and R
R
=
. Solve for R
R
⋅
⋅
sum
CS2
1
1
0
sum
+
−
where a=0, b=-Rsum, and
into the R
, which can then be rearranged to
+
CS2
1
1
R
−
−
. Use the higher value resistor
2
eq
4
2
4
⋅
⋅
⋅
R
R
R
R
R
eq
SUM
SUM
CS1
sum
eq
.
eq
eq
equation the following
that is larger than
=
CS1
0
.
or R
CS2
. The next
09/09/08
CS1
.