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IR3721のメーカーはInternational Rectifierです、この部品の機能は「Power Monitor IC」です。 |
部品番号 | IR3721 |
| |
部品説明 | Power Monitor IC | ||
メーカ | International Rectifier | ||
ロゴ | |||
このページの下部にプレビューとIR3721ダウンロード(pdfファイル)リンクがあります。 Total 16 pages
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FEATURES
Accurate TruePowerTM monitor
• 2.5% static accuracy
• Minimizes dynamic errors
Minimizes power dissipation
• 5mV - 150mV full scale current range
Versatile
• Monitors power or current
• Single buck or multiphase converters
• Inductor DCR or resistive shunt sensing
Simple add-on to existing converters
10 pin 3x3 DFN lead free package
RoHS compliant
IR3721
DATA SHEET
Power Monitor IC with
Analog Output
DESCRIPTION
The IR3721 is a versatile power or current monitor IC
for low-voltage DC-DC converters. The IR3721
monitors the inductor current in buck or multiphase
converters using either a current sensing resistor or the
inductor’s winding resistance (DCR). The output (DI) is
a pulse code modulated signal whose duty ratio is
proportional to the inductor current. An analog voltage
that is proportional to power is realized by connecting
VK to VO and connecting an RC filter to DI.
The IR3721 uses Patent Pending TruePowerTM
technology to accurately capture highly dynamic power
waveforms typical of microprocessor loads.
TYPICAL APPLICATION CIRCUIT
ORDERING INFORMATION
Device
IR3721MTRPBF
* IR3721MPBF
Package
10 lead DFN (3x3 mm body)
10 lead DFN (3x3 mm body)
* Samples only
Page 1 of 16
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Order Quantity
3000 piece reel
121 piece tube
07/14/08
1 Page BLOCK DIAGRAM
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VDD
VO VO result out
VCS
VRT
IREF IREF
TruePower™
VCS
result out/
IR3721
GND
IR3721
DATA SHEET
VK
DI
IC PIN DESCRIPTION
NAME
VCS
VO
VRT
GND
VDD
GND
GND
DI
VK
VDD
BASE PAD
NUMBER
1
2
3
4
5
6
7
8
9
10
I/O LEVEL
Analog
Analog
Analog
3.3V
Analog
1.8V
3.3V
DESCRIPTION
Current sensing input, connect through resistor to sensing node
Current sensing reference connect to output voltage
RT thermistor network from this pin to GND programs thermal monitor
Bias return and signal reference
IC bias supply
Connect to pin 4
Connect to pin 4
Power Monitor output; connect to output filter
Connect to fixed voltage or VO, multiplied by DI to become analog output
Connect to pin 5
Connect to pin 4
Page 3 of 16
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07/14/08
3Pages IR3721
DATA SHEET
THERMAL COMPENSATION FOR INDUCTOR DCR CURRENT
SENSING
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the inductor
inversely
proportional to the DCR. DCR of a copper coil, as a
function of temperature, is approximated by
Rth
(T
)
=
Rth
(T0
)
⋅
⎜⎛
e ⎜⎝
β
⎜⎜⎝⎛
1
T
-
1
T0
⎟⎟⎠⎞
⎟⎞
⎟⎠
Equation 3
DCR(T ) = DCR(TR ) ⋅ (1+ (T - TR ) ⋅TCRCu )
Equation 2
TR is some reference temperature, usually 25 °C, and
TCRCu is the resistive temperature coefficient of
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(TR) at the reference temperature.
If RT incorporates a negative temperature coefficient
thermistor then temperature effects of DCR can be
minimized. Consider a circuit of two resistors and a
thermistor as shown below.
where Rth(T) is the thermistor resistance at some
temperature T, Rth(T0) is the thermistor resistance at
the reference temperature T0, and β is the material
constant provided by the thermistor manufacturer.
Kelvin degrees are used in the exponential term of
equation 3. If RS is large and RP is small, the
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 RT of the network shown as a
function of temperature is
Rs
Rp Rth
Figure 2 RT Network
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
RT (T ) = Rs + 1
1
1
Rp + Rth (T )
Equation 4
using Rth(T) from equation 3.
Equation 2 may be rewritten as a new function of
temperature using equations 2 and 4 as follows:
( )IFS (T) =
VRΤ
RT (T
)
⋅
RCS1 + RCS2
DCR(T)
Equation 5
With Rs and Rp as additional free variables, use a
spreadsheet to solve equation 5 for the desired full
scale current while minimizing the IFS(T) variation
over temperature.
Page 6 of 16
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07/14/08
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部品番号 | 部品説明 | メーカ |
IR3720 | Power Monitor IC | International Rectifier |
IR3721 | Power Monitor IC | International Rectifier |
IR3725 | Input Power Monitor IC | International Rectifier |