IR3725MTRPBF International Rectifier, IR3725MTRPBF Datasheet - Page 12

• Manufacturer Part Number: IR3725MTRPBF
• Description: IC PWR MONITOR INPUT 12-DFN
• Manufacturer: International Rectifier
• Series: TruePower™r

Specifications of IR3725MTRPBF

• Applications: Power Supply Monitor
• Voltage - Supply: 3.135 V ~ 3.465 V
• Current - Supply: 700µA
• Operating Temperature: 0°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 12-VFDFN Exposed Pad
• Package: 12 Lead DFN
• 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: IR3725MTRPBFTR

ERROR MANAGEMENT
Component value errors external to the IR3725
contribute to power and current measurement error.
The power reported by the IR3725 is a function not
only of actual power or current, but also of products
and quotients of R
well as parameters internal to the IR3725. The
tolerance of these components increases the total
power or current error. Small signal resistors are
typically available in 1% tolerance, but 0.1% parts are
available. Shunts are also available at 1% or 0.1%
tolerance. The DCR tolerance of inductors can be
5%, but 3% are available. Fortunately, it is not typical
that worst-case errors would systematically stack in
one direction. It is statistically likely that a high going
value would be paired with a low going value to
somewhat cancel the error. Because of this,
tolerances can be added in quadrature (RSS). As an
example, a 3% DCR used with a 1% R
and 1.5% IR3725 contributes
error to a typical system.
LAYOUT GUIDELINES
The following guidelines will minimize noise and
error. Refer to the Functional Description Diagram.
Page 12 of 19
(
0
.
1. Bypass VDD to GND with a high quality
2. Place Ccs2 close to IC pins Vcs1 and Vcs2.
3. Sense the current sensing element at its
4. If inductor DCR current sensing is used,
03
)
2
ceramic capacitor.
Route Vcs1 and Vcs2 to the current sensing
element as a differential pair.
terminals, Kelvin style. Current and power
will be over reported if printed wire board
resistance is included between the sense
points.
place the compensating thermistor near the
inductor. Route the thermistor leads back to
the vicinity of the IC with differential routing.
Void any vias going to ground along the path
back until near the IC. Locate the thermistor
network (not the thermistor) near the IC.
+
(
0
.
01
)
2
T
+
, R
(
0
CS1
.
01
, R
)
2
CS2
+
(
0
, DCR (or R
.
015
)
2
T
≈
, a 1% R
3
.
SHUNT
6
www.irf.com
%
), as
CS
,
Quantization error occurs in digital systems because
the full scale is partitioned into a finite number of
intervals and the number of the interval containing
the measured value is reported. It is not likely that the
measured value would correspond exactly to the
center of the interval. The error could be as large as
half the width of the interval. With a binary word size
of eight, full scale is partitioned into 255 intervals.
Consider a measurement made near full scale. Any
signal in this interval is less than ± .2% (one-half of
100% / 256) away from the interval’s center, and
would therefore never have more error than that due
to quantization. On the other hand, consider a
measurement at one-tenth full scale. One-half of an
interval size at this level corresponds to 2% of the
reported value! Relative quantization error increases
as the measured value becomes small compared to
the full-scale value.
Quantization error can be reduced by averaging a
sequence of returned values.
5. VO should sense the voltage at the point of
6. Use an isolated dedicated ground plane
7. Do not connect pin 12 to any electrically
interest. Bypass VO to GND with a high
quality ceramic capacitor near the IC.
connected only to grounded components
associated with the IC in the figure. Connect
this dedicated ground plane at one location
to the ground of the monitored voltage.
active node.
IR3725
Data Sheet
2008_12_09