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PDF IR3725 Data sheet ( Hoja de datos )
| Número de pieza | IR3725 | |
| Descripción | Input Power Monitor IC | |
| Fabricantes | International Rectifier | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de IR3725 (archivo pdf) en la parte inferior de esta página. Total 19 Páginas | ||
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FEATURESwww.datasheet4u.com
Accurate power, current, or voltage reporting
1.5 % maximum power error
1.0 % maximum current error
Serial digital interface
SMBus and I2C compatible
Programmable averaging interval
Flexible current sensing
Resistive or Inductor DCR
Applications
Synchronous rectified buck converters
Multiphase converters
12pin 3x4 DFN lead free
RoHS Compliant
IR3725
Data Sheet
INPUT POWER MONITOR
WITH DIGITAL INTERFACE
DESCRIPTION
The IR3725 is a highly configurable power monitor IC
that uses proprietary digital technology to measure a
12V rail current, its voltage, or its average power over a
user specified time interval. Configuration and result
reporting are managed through a serial digital interface.
The current is measured as a voltage across a shunt
resistance, an input inductor, or a copper trace
resistance.
The real time voltage and current signals are multiplied,
digitized, and averaged over a user selectable
averaging interval providing TruePower™ measurement
of highly dynamic loads.
TYPICAL APPLICATION CIRCUIT
+12V
L DCR
CCS1
CCS2
+12V Return
Input
Capacitors
Buck Regulators
3.3V
VDD
IR3725 I2C
VO ALERT#
VCS2
VT
VCS1 ADDR
GND
To system
Controller
2
RT 0.1 uF
ORDERING INFORMATION
Device
IR3725MTRPBF
IR3725MPBF
Package
12 lead DFN (4x3 mm body)
12 lead DFN (4x3 mm body)
Order Quantity
3000 piece reel
Sample Quantity
Page 1 of 19
www.irf.com
2008_12_09
1 page  
IR3725
Data Sheet
ADDR PIN
The ADDR pin is an input that establishes the serial
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Table 1, “User Selectable Addresses”, provides a
mapping of possible selections. Bypass this pin to
GND with a high quality ceramic capacitor when
floated.
Table 1 User selectable addresses
ADDR pin configuration
Low
Open
High
Bus Address
b’1110 000
b’1110 010
b’1110 110
EXTCLK
This pin is a Schmitt trigger input for an optional
externally provided square wave clock. The duty ratio
of this externally provided clock, if used, shall be
between 40% and 60%. If no external clock is
connected, the internal clock will be used. Connect
this pin to GND if no external clock is used.
SCL
SCL is the serial bus clock and is capable of
functioning with a rate as low as 10 kHz. It will
continue to function as the rate is increased to 400
kHz. This device is considered a slave, and therefore
uses the SCL as an input only.
SDA
SDA is monitored as data input during master to
slave transactions, and is driven as data output
during slave to master transactions as indicated in
the Packet Protocol section to follow.
Page 5 of 19
www.irf.com
2008_12_09
5 Page 
IR3725
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
⎟⎟⎠⎞
⎟⎞
⎟⎠
(2)
DCR(T ) = DCR(TR ) ⋅ (1 + (T − TR ) ⋅ TCRCu ) .
(1)
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 1 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 in the RT network 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 2. 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 2 can never
compensate linear equation 1 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
Rs
RT (T) = Rs + 1
1
1
Rp + Rth (T)
(3)
Rp Rth
Figure 3 RT Network
If Rth is an NTC thermistor then the resistance 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
using Rth(T) from equation 2.
Equation 4 may be written as a function of
temperature using equations 1 and 3 as follows:
( )IFS (T) =
VIG
RT (T
)
⋅
RCS1 + RCS2
DCR(T)
.
(4)
With Rs and Rp as additional free variables, use a
spreadsheet to solve equation 4 for the desired full
scale current while minimizing the IFS(T) variation
over temperature.
Page 11 of 19
www.irf.com
2008_12_09
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet IR3725.PDF ] | |
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