IR3720MTRPBF International Rectifier, IR3720MTRPBF Datasheet - Page 11

• 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

THERMAL COMPENSATION FOR INDUCTOR DCR CURRENT
SENSING
The positive temperature coefficient of the DCR can
be compensated if R
the DCR. DCR of a copper coil, as a function of
temperature, is approximated by
T
TCR
copper, usually assumed to be 0.0039 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 3 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 11 of 20
Rp
R
is some reference temperature, usually 25 °C, and
T
DCR
Cu
incorporates a negative temperature coefficient
Rs
R
R
is the resistive temperature coefficient of
th
) at the reference temperature.
(
(
T
T
)
)
T
=
=
Network
DCR
R
Rth
th
(
T
(
0
T
)
R
T
⋅
)
e
varies inversely proportional to
⋅
⎛
⎜
⎜
⎝
1 (
β
⋅
⎛
⎜
⎜
⎝
+
T
1
(
−
T
T
1
0
−
⎞
⎟
⎟
⎠
⎞
⎟
⎟
⎠
T
R
)
⋅
TCR
Cu
)
www.irf.com
.
(2)
(3)
where R
temperature T, R
the reference temperature T
constant provided by the thermistor manufacturer.
Degrees Kelvin are used in equation 3. If R
and R
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 resistance R
function of temperature is
using R
Equation 1 of the last section 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.
P
is small, the curvature of the effective network
th
th
(T) from equation 3.
I
FS
(T) is the thermistor resistance at some
R
(
T
T
(
)
T
=
)
th
=
R
(T
V
T
R
IG
(
0
s
T
) is the thermistor resistance at
+
)
⋅
R
(
1
R
T
p
CS
of the network shown as a
DCR
+
0
, and β is the material
1
1
R
+
th
1
R
(
(
T
T
CS
)
)
FS
2
(T) variation
)
.
S
is large
09/09/08
(4)
(5)