IR3725
Data Sheet
INPUT POWER MONITOR
WITH DIGITAL INTERFACE
FEATURES
Accurate power, current, or voltage reporting
1.5 % maximum power error
1.0 % maximum current error
Serial digital interface
SMBus and I
2
C 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
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
Input
Capacitors
Buck Regulators
3.3V
VDD
To system
Controller
DCR
C
CS1
IR3725
VO
I
2
C
C
CS2
ALERT#
2
VT
VCS2
ADDR
VCS1
GND
R
T
0.1 uF
+12V Return
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
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IR3725
Data Sheet
ABSOLUTE MAXIMUM RATINGS
All voltages referenced to GND
VDD: ................................................................ 3.9V
ALERT#:........................................................... 3.9V
ALERT#............................................. < VDD + 0.3V
VCS1, VCS2, VO ........................................... 25.0V
All other Analog and Digital pins ...................... 3.9V
Operating Junction Temperature .... -10°C to 150
o
C
Storage Temperature Range .......... -65
o
C to 150
o
C
Thermal Impedance (θ
JC
).......................... 1.6 °C/W
Thermal Impedance (θ
JA
) ........................... 30 °C/W
ESD Rating ......... HBM Class 1C JEDEC Standard
MSL Rating .................................................. Level 2
Reflow Temperature ..................................... 260°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device.
These are stress ratings only and functional operation of the device at these or any other conditions beyond those
indicated in the operational sections of the specifications are not implied. Exposure to absolute maximum rating
conditions for extended periods may affect device reliability.
VDD = 3.3V ± 5%, 0 C
≤
T
J
≤
125 C, 8V
≤
VO
≤
23.5V, and operation in the typical application circuit. See notes
following table.
PARAMETER
BIAS SUPPLY
VDD Turn-on Threshold, VDD
UP
VDD Turn-off Threshold, VDD
DN
VDD UVLO Hysteresis
VDD Operating Current
VDD Shutdown Current
VOLTAGE REFERENCE
V
T
Voltage
Reference load, R
T
VOLTAGE SENSOR
Voltage, full scale, V
FS
CURRENT SENSOR
Voltage, Current Gain, V
IG
DIGITIZER
Internal Sampling frequency
External Sampling frequency
POWER INFORMATION
Minimum Averaging Interval
Maximum Averaging Interval
TEST CONDITION
NOTE
MIN
TYP
MAX
3.1
2.4
75
R
T
= 25.5 kΩ
Config Reg enable bit d4=1
R
T
= 25.5 kΩ
1
1.40
20
700
18
1.50
25.5
23.5
R
T
= 25.5 kΩ
Driven from internal clock
Driven from external clock
Config Reg [d3..d0] = b‘0000
Config Reg [d3..d0] = b‘1000
1
1
1.48
512
1024
1
256
1000
100
1.60
45.3
UNIT
V
V
mV
A
A
V
kΩ
V
V
kHz
kHz
ms
ms
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply:
o
o
922
0.85
217
1126
1.15
295
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IR3725
Data Sheet
PARAMETER
ACCURACY
Power measurement error
TEST CONDITION
VO=12V, DCR voltage = 75 mV,
R
T
=25.5kΩ, RCS1=RCS2=1.5kΩ
T
j
= 0 - 85 °C
VO=12 V, DCR voltage = 75mV,
RT=25.5kΩ, RCS1=RCS2=1.5kΩ
Tj = 0 – 85 °C
VO=12V, DCR voltage = 75 mV,
R
T
=25.5kΩ, RCS1=RCS2=1.5kΩ
Tj = 0 – 85 °C
NOTE
MIN
TYP
MAX
2
1.5
UNIT
1, 2
%
Voltage measurement error
1, 2
1.5
1.3
%
Current measurement error
1, 2
1.6
%
NOTES:
1.
2.
Guaranteed by design, not tested in production
Assumes no error contributed by external components
BLOCK DIAGRAM
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IR3725
Data Sheet
PIN DESCRIPTION
NAME
VCS1
VCS2
VO
VT
GND
VDD
EXTCLK
ADDR
SCL
SDA
ALERT#
NC
NUMBER
1
2
3
4
5
6
7
8
9
10
11
12
I/O LEVEL
Analog 12V
Analog 12V
Analog 12V
Analog
0V
3.3V
3.3V Digital
3.3V Digital
3.3V Digital
3.3V Digital
3.3V Digital
DESCRIPTION
Current sensing input 1
Current sensing input 2
Voltage sensing input
Thermistor sensing input
IC bias supply and signal ground
3.3V bias supply
Input for optional external clock
Bus Address selection input
Bus Clock; Input only
Bus Data; Input / Open drain output
Programmable output function; Open drain output clamped to VDD
Do not connect
IC PIN FUNCTIONS
VDD PIN
This pin provides operational bias current to circuits
internal to the IR3725. Bypass it with a high quality
ceramic capacitor to the GND pin.
GND PIN
This pin returns operational bias current to its source.
It is also the reference to which the voltage VO is
measured, and it sinks the reference current
established by the external resistor R
T
.
VO PIN
This pin is to be electrically connected to the location
in the circuit where voltage for the power calculation
is desired to be monitored. Power accuracy may be
degraded if the voltage at this pin is below VO
min
.
VCS1 AND VCS2 PINS
The average current into these pins is used to
calculate power. Current sources internal to the
IR3725 will null the average voltage between this pin
pair.
VT FUNCTION
A voltage internal to the IR3725 drives the VT pin
while the pin current is monitored and used to set the
amplitude of the switched current source IT. This pin
should be connected to GND through a precision
resistor network RT. This network may include
provision for canceling the positive temperature
coefficient of the inductor’s DC resistance (DCR).
ALERT# FUNCTION
The ALERT# pin is a multi-use pin. During normal
use it can be configured via the serial bus as an open
drain ALERT# pin that will be driven logic low when
new data is available in the output register. After the
output register has been read via the serial bus the
ALERT# will be released to its high resistance state.
This pin can also be programmed to pull low when
the output exceeds the programmable level.
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IR3725
Data Sheet
ADDR PIN
The ADDR pin is an input that establishes the serial
bus address. Valid addresses are selected by
grounding, floating, or wiring to VDD the ADDR pin.
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
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.
Bus Address
b’1110 000
b’1110 010
b’1110 110
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.
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