International Rectifier IR3721, IR3721MPBF Datasheet

IR3721

DATA SHEET

Power Monitor IC with

Analog Output

FEATURES

 Accurate TruePower

• 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

TM

monitor

TYPICAL APPLICATION CIRCUIT

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
V

to VO and connecting an RC filter to DI.

K

The IR3721 uses Patent Pending TruePower

technology to accurately capture highly dynamic power
waveforms typical of microprocessor loads.

TM

ORDERING INFORMATION

Device Package Order Quantity
IR3721MTRPBF 10 lead DFN (3x3 mm body) 3000 piece reel
IR3721MPBF 10 lead DFN (3x3 mm body) Sample Quantity

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ABSOLUTE MAXIMUM RATINGS

IR3721

DATA SHEET

Absolute Maximum Ratings (Referenced to GND)

VDD:.................................................................3.9V

All other Analog and Digital pins......................3.9V

Operating Junction Temperature .... -10°C to 150°C

Storage Temperature Range .......... -65°C to 150°C

ESD Rating ............HBM Class 2 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.

ELECTRICAL SPECIFICATIONS

Unless otherwise specified, these specifications apply: VDD = 3.3V ± 5%, 0oC ≤ TJ ≤ 125oC, 0.5 ≤ Vo ≤ 1.8 V, and
operation in the typical application circuit. See notes following table.

PARAMETER TEST CONDITION MIN TYP MAX UNIT

BIAS SUPPLY

VDD Turn-on Threshold, VDDUP 3.10 V
VDD Turn-off Threshold, VDDDN 2.4 V
VDD UVLO Hysteresis DI output low when off 75 mV
VDD Operating Current, ICC 350 450 μA

VOLTAGE REFERENCE

VRT Voltage RT = 25.5k Ω 1.452 1.493 1.535 V
RT resistance range Note 1 25.5

ΔΣ CONVERTER

Vo common mode range 0.5 1.8 V
Duty Ratio Accuracy V

Duty Ratio Accuracy V

=20 mV, VO=1V,

DCR

R

=25.5kΩ, R

T

T

=65°C, Note 1

j

=20 mV, VO=1V,

DCR

=25.5kΩ, R

R

T

CS1+RCS2

CS1+RCS2

2.5 %

=600 Ω

4 %

=600 Ω,

Note 1

Sampling frequency, f

435 512 589 kHz

CLK

Comparator Offset -0.5 +0.5 mV
CS pin input current, ICS DI output low -250 +250 nA

DIGITAL OUTPUT

VK pin voltage range 0.5 1.8 V
DI source resistance 1250 2000 3000

NOTES:

1. Guaranteed by design

kΩ

Ω

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BLOCK DIAGRAM

IR3721

DATA SHEET

VDD

VK

VO

VCS

V

RT

I

REF

I

REF

VO

TruePower™

VCS

result out

DI

result out/

IR3721

GND

IC PIN DESCRIPTION

NAME NUMBER I/O LEVEL DESCRIPTION

VCS 1 Analog Current sensing input, connect through resistor to sensing node
VO 2 Analog Current sensing reference connect to output voltage
VRT 3 Analog RT thermistor network from this pin to GND programs thermal monitor
GND 4
VDD 5 3.3V IC bias supply
GND 6 Connect to pin 4
GND 7 Connect to pin 4
DI 8 Analog Power Monitor output; connect to output filter
VK 9 1.8V Connect to fixed voltage or VO, multiplied by DI to become analog output
VDD 10 3.3V Connect to pin 5
BASE PAD Connect to pin 4

Bias return and signal reference

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IC PIN FUNCTIONS

VDD PINS

IR3721

DATA SHEET

VRT PIN

These pins provide operational bias current to circuits
internal to the IR3721. Bypass them with a high
quality ceramic capacitor to the GND pins.

GND PINS

These pins return operational bias current to system
ground. VO is measured with respect to GND. The
GND pin sinks reference current established by the
external resistor R

.

T

VO PIN

Since this pin measures DCR voltage drop it is critical
that it be Kelvin connected to the buck inductor
output. Power accuracy may be degraded if the
voltage at this pin is below VO

min

.

VCS PIN

A switched current source internal to the IR3721
maintains the average voltage of this pin equal to the
voltage of the VO pin. The average current into this
pin is therefore proportional to buck inductor current.

A voltage reference internal to the IR3721 drives the
V

pin while the pin current is monitored and used to

RT

set the amplitude of the current monitor switched
current source I
a precision resistor network R

. Connect this pin to GND through

REF

. This network may

T

include provision for canceling the positive
temperature coefficient of the buck inductor’s DC
resistance (DCR).

VK PIN

The voltage of the VK pin is used to modulate the
amplitude of the DI pin. This is one of the terms used
to determine the product of the multiplier output. If VK
is connected to a fixed voltage then the output of the
multiplier is proportional to current. If VK is connected
to the buck converter output voltage then the output
of the DI driven RC filter is proportional to power.

DI PIN

The Dl pin output has a duty ratio proportional to the
current into VCS, and an amplitude equal to the
voltage at the VK pin. The DI pin is intended to drive
an external low pass filter. The output of this filter is
the product of the current and voltage terms.

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FUNCTIONAL DESCRIPTION

Please refer to the Functional Description Diagram
below. Power flow from the buck converter inductor is
the product of output voltage times the current I

L

flowing through the inductor.

Power is measured with the aid of International
Rectifier’s proprietary TruePower™ circuit. Current is
converted to a duty ratio that appears at the DI pin.
The duty ratio of the DI pin is

DI

RATIODUTY

RR

⋅

DCRI

L

=

R

T

⋅

)+(

2CS1CS

V

Τ

R

Equation 1

The full-scale current that can be measured
corresponds to a duty ratio of one.

I

L

Vin

R

L

CS1

DCR

C

CS1

C

CS2

VCS

R

CS2

VO

The amplitude of the DI pin is the voltage appearing
at pin VK. If a fixed voltage is applied to VK then the
output of the RC filter driven by DI will be proportional
to inductor current I

.

L

If VO is applied to V

as shown in the figure then the

K

output of the DI driven RC network will be
proportional to power. The full-scale voltage that can
be measured is established on the chip to be 1.8V.

The full scale power P

that can be measured is the

FS

product of full-scale voltage and full scale current.

Vo

VDD

VK

IR3721

DI

Power

V

RT

R

T

GND

Figure 1 Functional Description Diagram

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