IR3721MPBF International Rectifier, IR3721MPBF Datasheet - Page 6
![no-image](/images/manufacturer_photos/0/3/338/international_rectifier_sml.jpg)
IR3721MPBF
Manufacturer Part Number
IR3721MPBF
Description
Power Monitor IC with Analog Output
Manufacturer
International Rectifier
Datasheet
1.IR3721MPBF.pdf
(16 pages)
Specifications of IR3721MPBF
Package
10 Lead 3x3 DFN
Static Accuracy
2.5% @ 65oC
Vk Range
0.5V - 1.8V
Vcs Range
5mV - 150mV
Bias Supply Voltage
+3.3V +/-5%
Junction Temperature
0oC to 125oC
Pbf
Yes
THERMAL COMPENSATION FOR INDUCTOR DCR CURRENT
SENSING
The positive temperature coefficient of the inductor
DCR can be compensated if R
proportional to the DCR. DCR of a copper coil, as a
function of temperature, is approximated by
T
TCR
copper, usually assumed to be 0.39 %/°C near room
temperature. Note that equation 2 is linearly
increasing with temperature and has an offset of
DCR(T
If R
thermistor then temperature effects of DCR can be
minimized. Consider a circuit of two resistors and a
thermistor as shown below.
Figure 2 R
If Rth is an NTC thermistor then the value of the
network will decrease as temperature increases.
Unfortunately, most thermistors exhibit far more
variation with temperature than copper wire. One
equation used to model thermistors is
Page 6 of 16
Rp
R
is some reference temperature, usually 25 °C, and
T
Cu
incorporates a negative temperature coefficient
Rs
DCR
R
is the resistive temperature coefficient of
) at the reference temperature.
(
T
T
Network
)
=
Rth
DCR
Equation 2
(
T
R
)
( ⋅
1
+
T
(
T
varies inversely
-
T
R
⋅ )
TCR
www.irf.com
Cu
)
where R
temperature T, R
the reference temperature T
constant provided by the thermistor manufacturer.
Kelvin degrees are used in the exponential term of
equation 3. If R
curvature of the equivalent network resistance can be
reduced from the curvature of the thermistor alone.
Although the exponential equation 3 can never
compensate linear equation 2 at all temperatures, a
spreadsheet can be constructed to minimize error
over the temperature interval of interest. The
equivalent resistance R
function of temperature is
using R
Equation 2 may be rewritten as a new function of
temperature using equations 2 and 4 as follows:
With Rs and Rp as additional free variables, use a
spreadsheet to solve equation 5 for the desired full
scale current while minimizing the I
over temperature.
th
th
(T) from equation 3.
(T) is the thermistor resistance at some
I
FS
R
R
th
(
T
S
T
(
T
(
is large and R
)
th
T
)
(T
=
)
=
=
R
0
Equation 3
Equation 4
Equation 5
) is the thermistor resistance at
R
V
R
T
R
th
T
(
s
Τ
T
(
of the network shown as a
T
+
)
0
⋅
R
⋅ )
0
(
1
R
, and β is the material
p
e
CS
P
DCR
+
⎛
⎜
⎜
⎝
β
is small, the
1
1
R
+
⎛
⎜
⎜
⎝
th
FS
T
1
R
(
1
DATA SHEET
(
T
-
(T) variation
T
CS
T
)
1
0
)
IR3721
⎞
⎟
⎟
⎠
2
⎞
⎟
⎟
⎠
)
09/15/08