IR3721MTRPBF International Rectifier, IR3721MTRPBF Datasheet - Page 6

• Manufacturer Part Number: IR3721MTRPBF
• Description: IC POWER SUPPLY MONITOR 10-DFN
• Manufacturer: International Rectifier
• Series: TruePower™r

Specifications of IR3721MTRPBF

• Applications: Power Supply Monitor
• Voltage - Supply: 3.135 V ~ 3.465 V
• Current - Supply: 350µA
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 10-DFN
• Quiescent Current: 450µA
• Bandwidth: 589kHz
• Sensor Case Style: DFN
• No. Of Pins: 10
• Supply Voltage Range: 3.135V To 3.465V
• Operating Temperature Range: 0°C To +125°C
• Filter Terminals: SMD
• Rohs Compliant: No
• Accuracy %: 2.5%
• 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
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -
• Other names: IR3721MTRPBFTR

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