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PDF IR3720 Data sheet ( Hoja de datos )
| Número de pieza | IR3720 | |
| Descripción | Power Monitor IC | |
| Fabricantes | International Rectifier | |
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IR3720
DATA SHEET
www.datasheet4u.com
FEATURES
Accurate TruePower™ monitor
• Minimizes dynamic errors
• Reports voltage, current, or power
Digital interface
• SMBus and I2C compatible
Programmable averaging interval
Flexible current sensing
• Resistive or Inductor DCR
Applications
• Synchronous rectified buck converters
• Multiphase converters
10pin 3x3 DFN lead free package
RoHS compliant
Power Monitor IC with
Digital I2C Interface
DESCRIPTION
The IR3720 measures the output voltage and inductor
current of low-voltage DC-to-DC converters and reports
the average power over a user specified time interval as
a digital word on the I2C. The output current is
measured across a current sensing resistor or indirectly
across the inductor’s DCR winding resistance.
Additionally, the current measurement method is also
applicable to multiphase converters.
The real time voltage and current signals are multiplied,
digitized, and averaged over a user selectable
averaging interval providing Patent Pending
TruePower™ measurement of highly dynamic loads.
TYPICAL APPLICATION CIRCUIT
Phase
Single
Phase
Converter
Power
Return
DCR
L
Rcs1
Rcs2
CCS1
CCS2
3.3V
Output
Capacitors
LOAD
VO VDD
IR3720
I2C Bus
VCS VREF
GND
To system
Controller
2
RT
GND
ORDERING INFORMATION
Device
IR3720MTRPBF
* IR3720MPBF
* Samples only
Package
10 lead DFN (3x3 mm body)
10 lead DFN (3x3 mm body)
Order Quantity
3000 piece reel
121 Piece tube
Page 1 of 20
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09/09/08
1 page  
BLOCK DIAGRAM
www.datasheet4u.com
IR3720
DATA SHEET
IC PIN DESCRIPTION
NAME
VCS
VO
VREF
GND
VDD
EXTCLK
ADDR
SCL
SDA
ALERT#
BASE PAD
NUMBER
1
2
3
4
5
6
7
8
9
10
I/O LEVEL
Analog
Analog
Analog
3.3V
3.3V Digital
3.3V Digital
3.3V Digital
3.3V Digital
3.3V Digital
DESCRIPTION
Current sensing input
Voltage sensing input
Thermistor sensing input
IC bias supply and signal ground
3.3V bias supply
Input for optional external clock
I2C Address selection input; See Table 1 for address
I2C Clock; Input only
I2C Data; Input / Open drain output
Programmable output function; Open drain output clamped to VDD
Connect to pin 4
Page 5 of 20
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09/09/08
5 Page 
THERMAL COMPENSATION FOR INDUCTOR DCR CURRENT
SENSING
The positive temperature coefficient of the DCR can
be compensated if RT varies inversely proportional to
the DCR. DCR of a copper coil, as a function of
temperature, is approximated by
www.datasDheCeRt4(uT.c)om= DCR(TR ) ⋅ (1 + (T − TR ) ⋅ TCRCu ) .
(2)
TR is some reference temperature, usually 25 °C, and
TCRCu is the resistive temperature coefficient of
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(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.
Degrees Kelvin are used in equation 3. If RS is large
and RP is small, the curvature of the effective 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 resistance RT of the network shown as a
function of temperature is
RT(T) = Rs + 1
1
1
Rp + Rth(T)
(4)
Rs
Rp Rth
using Rth(T) from equation 3.
Equation 1 of the last section may be rewritten as a
new function of temperature using equations 2 and 4
as follows:
( )IFS(T) =
VIG
RT (T
)
⋅
RCS1 + RCS2
DCR(T)
.
(5)
Figure 3 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
Rth (T )
=
Rth (T0 )
⋅
e
⎜⎛
⎜⎝
β
⋅⎜⎜⎝⎛
1
T
− T10
⎟⎟⎠⎞
⎟⎞
⎟⎠
(3)
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 11 of 20
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09/09/08
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet IR3720.PDF ] | |
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