IR3721_09 [INFINEON]
Power Monitor IC with; 电源监控器IC与
| 型号： | IR3721_09 |
| 厂家： | 
Infineon |
| 描述： | Power Monitor IC with |
| 文件： | 总16页 (文件大小：335K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
IR3721
DATA SHEET
Power Monitor IC with
Analog Output
FEATURES
DESCRIPTION
Accurate TruePowerTM monitor
• 2.5% static accuracy
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
VK to VO and connecting an RC filter to DI.
• 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
The IR3721 uses Patent Pending TruePowerTM
technology to accurately capture highly dynamic power
waveforms typical of microprocessor loads.
TYPICAL APPLICATION CIRCUIT
ORDERING INFORMATION
Device
Package
Order Quantity
IR3721MTRPBF
* IR3721MPBF
10 lead DFN (3x3 mm body)
10 lead DFN (3x3 mm body)
3000 piece reel
121 piece tube
*
Samples only
Page 1 of 16
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09/15/08
IR3721
DATA SHEET
ABSOLUTE MAXIMUM RATINGS
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
BIAS SUPPLY
TEST CONDITION
MIN
TYP
MAX
UNIT
VDD Turn-on Threshold, VDDUP
VDD Turn-off Threshold, VDDDN
VDD UVLO Hysteresis
VDD Operating Current, ICC
VOLTAGE REFERENCE
VRT Voltage
3.10
V
V
2.4
75
DI output low when off
mV
μA
350
450
RT = 25.5k Ω
1.452 1.493 1.535
25.5
V
RT resistance range
Note 1
kΩ
ΔΣ CONVERTER
Vo common mode range
Duty Ratio Accuracy
0.5
1.8
2.5
V
VDCR=20 mV, VO=1V,
RT=25.5kΩ, RCS1+RCS2=600 Ω
Tj=65°C, Note 1
%
Duty Ratio Accuracy
VDCR=20 mV, VO=1V,
RT=25.5kΩ, RCS1+RCS2=600 Ω,
Note 1
4
%
Sampling frequency, fCLK
Comparator Offset
435
-0.5
-250
512
589
+0.5
+250
kHz
mV
nA
CS pin input current, ICS
DIGITAL OUTPUT
DI output low
VK pin voltage range
DI source resistance
0.5
1.8
V
1250
2000
3000
Ω
NOTES:
1.
Guaranteed by design
Page 2 of 16
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IR3721
DATA SHEET
BLOCK DIAGRAM
VDD
VK
DI
VO
VO
result out
TruePower™
VCS
VCS
VRT
IREF
IREF
result out/
IR3721
GND
IC PIN DESCRIPTION
NAME
VCS
VO
NUMBER I/O LEVEL DESCRIPTION
1
2
Analog
Analog
Analog
Current sensing input, connect through resistor to sensing node
Current sensing reference connect to output voltage
RT thermistor network from this pin to GND programs thermal monitor
Bias return and signal reference
VRT
3
GND
VDD
GND
GND
DI
4
5
3.3V
IC bias supply
6
Connect to pin 4
7
Connect to pin 4
8
Analog
1.8V
Power Monitor output; connect to output filter
Connect to fixed voltage or VO, multiplied by DI to become analog output
Connect to pin 5
VK
9
VDD
BASE PAD
10
3.3V
Connect to pin 4
Page 3 of 16
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IR3721
DATA SHEET
IC PIN FUNCTIONS
VDD PINS
VRT PIN
A voltage reference internal to the IR3721 drives the
These pins provide operational bias current to circuits
internal to the IR3721. Bypass them with a high
quality ceramic capacitor to the GND pins.
VRT pin while the pin current is monitored and used to
set the amplitude of the current monitor switched
current source IREF. Connect this pin to GND through
a precision resistor network RT. This network may
include provision for canceling the positive
temperature coefficient of the buck inductor’s DC
resistance (DCR).
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 RT.
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.
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 VOmin
.
VCS PIN
DI 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.
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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IR3721
DATA SHEET
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 IL
flowing through the inductor.
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 IL.
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
If VO is applied to VK as shown in the figure then the
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.
IL ⋅DCR
(RCS1 + RCS2 ) VRΤ
RT
DIDUTYRATIO
=
⋅
The full scale power PFS that can be measured is the
product of full-scale voltage and full scale current.
Equation 1
The full-scale current that can be measured
corresponds to a duty ratio of one.
IL
Vin
Vo
L
DCR
VDD
VK
VO
RCS1
CCS1
CCS2
VCS
DI
Power
IR3721
RCS2
VRT
RT
GND
Figure 1 Functional Description Diagram
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IR3721
DATA SHEET
THERMAL COMPENSATION FOR INDUCTOR DCR CURRENT
SENSING
The positive temperature coefficient of the inductor
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
⎛
⎜
⎞
⎟
⎟
⎠
⎛
⎜
⎜
⎝
⎞
⎟
⎟
⎠
1
1
β
-
Rth (T ) = Rth (T0 ) ⋅e⎝⎜
T
T0
Equation 3
DCR(T ) = DCR(TR ) ⋅ (1+ (T -TR ) ⋅TCRCu
)
Equation 2
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 3. 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 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
equivalent resistance RT of the network shown as a
function of temperature is
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 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.
1
RT (T ) = Rs +
1
1
Rs
+
Rp Rth (T )
Equation 4
Rp
Rth
using Rth(T) from equation 3.
Equation 2 may be rewritten as a new function of
temperature using equations 2 and 4 as follows:
Figure 2 RT Network
(
RCS1 + RCS2
DCR(T)
)
VRΤ
IFS (T) =
⋅
RT (T)
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
Equation 5
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 6 of 16
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IR3721
DATA SHEET
TYPICAL 2-PHASE DCR SENSING APPLICATION
The IR3721 is capable of monitoring power in a
multiphase converter. A Two Phase DCR Sensing
Circuit is shown below. The voltage output of any
phase is equal to that of any and every other phase
because they are electrically connected and
monitored at VO as before.
The duty ratio of DI is
ICS ⋅RT
VREF
DIDUTYRATIO
=
If DCR1=DCR2, and RCS1=RCS3, then ICS can be
simplified to
Output current is the sum of the two inductor currents
(IL1 + IL2). Superposition is used to derive the transfer
function for multiphase sensing. The voltage on RCS2
due to IL1 is
(IL1 + IL2 ) ⋅ DCR1
ICS
=
RCS1 + 2RCS2
(RCS2 || RCS3
RCS1 + (RCS2 || RCS3
)
IL1 ⋅DCR1 ⋅
and the DI duty ratio simplifies to
)
(IL1 + IL2 )⋅DCR⋅RT
(RCS1 + 2RCS2 )⋅ VRΤ
DIDUTYRATIO
=
Likewise, the voltage on RCS2 due to IL2 is
(RCS2 || RCS1
RCS3 + (RCS2 || RCS1
Full scale current occurs when DI duty ratio becomes
one.
)
IL2 ⋅ DCR2 ⋅
)
The current through RCS2 due to both inductor
currents is ICS. From the two equations above
IL1DCR1RCS3 + IL2DCR2RCS1
RCS1RCS2 + RCS1RCS3 + RCS2RCS3
ICS
=
Figure 3 Two Phase DCR Sensing Circuit
Page 7 of 16
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IR3721
DATA SHEET
RESISTOR SENSING APPLICATION
The Resistor Sensing Circuit shown below is an
example of resistive current sensing. Because the
voltage on the shunt resistor is directly proportional to
the current IL through the inductor, RCS2 and CCS2 do
not need to match the L / DCR time constant.
Because the value of the shunt resistance does not
change with temperature as the inductor DCR does,
RT can be a fixed resistor.
IL
SHUNT
VO
DCR
Phase 1
L
Buck
Converter
RCS2
Power
Return
CCS2
VDD
VDD
VO
VCS
VK
DI
VDD
Bypass
Cap
Power
IR3721
VRT
RT
GND
Figure 4 Resistor Sensing Circuit
Page 8 of 16
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IR3721
DATA SHEET
COMPONENT SELECTION GUIDELINES
Use a 0.1 μF, 6.3V, X7R ceramic bypass capacitor
from VDD to GND and from VK to GND.
Filter the DI output with an RC filter to give a stable
analog representation of the current or power. Some
of the DI source resistance of this filter is internal to
the IR3721 and specified in the electrical
26.1 kΩ, 1%
specifications table. Add twenty thousand to fifty
thousand additional ohms externally to minimize
resistance variation. As the DI source resistance
2.00 kΩ, 1%
15.0 kΩ, 1%
increases beyond these guidelines, the voltage
measurement error caused by non-ideal voltmeter
conductance will increase.
Murata Thermistor
NCP15WB473F03RC
47 kΩ, 1%
Select a filter capacitor that limits 512 kHz sampling
frequency ripple to an acceptable value. Sampling
frequency ripple will appear as an error, but can be
reduced 20 dB for each decade that the filter corner
frequency is below 512 kHz. Select a capacitor value
that achieves the desired balance between low
sampling frequency ripple and adequate bandwidth.
Figure 5 RT network
The resistance of the network above at 25°C, RT(25),
is 37.58kΩ. Over temperature RT(T) is multiplied by
copper resistance, DCR(25)·(1+(T-25)·0.0039),
divided by (DCR(25)·( RT(25)) to normalize the
results, and plotted as nominal error in Figure 6.
Resistor current sensing
For resistor current sensing select a precision resistor
for RT inside the RT resistance range limits specified
in the Electrical Specifications table, such as 25.5kΩ
and 1% tolerance.
Next, select a shunt resistor that will provide the most
current sensing voltage while also considering the
allowable power dissipation limitations. The DI output
will saturate to the VK voltage when full scale current
5%
4%
3%
2%
IFS flows through this shunt. Recommended
1%
maximum current sensing voltage range is 5 to 150
mV. Maximum sensing voltages less than 5 mV will
cause comparator input offset voltage errors to
dominate, and voltages larger than 150 mV will cause
comparator leakage current, ICS, errors to dominate.
Select RCS2 to be the next higher standard value
resistor from (RSHUNT·IFS·RT) / VRT in order to
accommodate full scale current IFS.
Bypass VCS to VO with capacitor CCS2. The value of
this capacitor limits the bandwidth, but is required
because it is the integrator of the delta sigma
modulator. Consider selecting the value of CCS2 to
place a filter corner frequency at 5 kHz, which will
reduce sampling ripple by 40 dB.
0%
-1%
-2%
-3%
-4%
-5%
0
20
40
60
80
100
Temperature [°C]
Figure 6 Nominal error vs. Temperature
Note that the error due to temperature compensation
at 25°C is zero, assuming ideal RT components. At
other temperatures the results are over or under
reported by the factor in percent indicated.
DCR current sensing
Proceed to calculate RSUM, defined as the sum of
R
CS1 plus RCS2, as follows.
RSUM=IFS·DCR(25) ·RT(25) / VRT
Select an RT network resistance between 20kΩ and
45.3kΩ. Consider the RT network of Figure 5 for DCR
current sensing.
Again, IFS is full scale current and VRT is the reference
voltage establishing the current in RT.
Estimate the capacitance CCS1 with the following
equation.
Page 9 of 16
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IR3721
DATA SHEET
4 ⋅ L
CCS 1
>
DCR (25 ) ⋅ RSUM
Choose a standard capacitor value larger than
indicated by the right hand side of the inequality
above.
Calculate the equivalent resistance Req.
R
eq = L / (DCR(25) ·CCS1)
We now have two equations, RSUM = RCS1 + RCS2 and
Req = (RCS1 · RCS2) / (RCS1 + RCS2). Calculate RCS1
and RCS2 using the following two equations.
⎛
⎜
⎞
⎟
Req
1+ 1- 4 ⋅
⎜
⎜
⎜
⎟
⎟
⎟
RSUM
RCS1 = RSUM
⋅
and
2
⎜
⎜
⎟
⎟
⎝
⎠
⎛
⎜
⎞
⎟
Req
1- 1- 4 ⋅
⎜
⎜
⎜
⎟
⎟
⎟
RSUM
RCS2 = RSUM
⋅
2
⎜
⎜
⎟
⎟
⎝
⎠
Use the next higher standard 1% value than indicated
in the equations above. This will insure that full scale
current can be measured.
Bypass VCS to VO with capacitor CCS2. The value of
this capacitor limits the bandwidth, but is required
because it is the integrator of the delta sigma
modulator. Consider selecting the value of CCS2 to
place a filter corner frequency at 5 kHz, which will
reduce sampling ripple by 40 dB.
Page 10 of 16
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IR3721
DATA SHEET
LAYOUT GUIDELINES
Refer to figures 7 through 11 for guidance laying out
the IR3721. These guidelines also apply to resistive
current sensing. The following guidelines will
minimize sources of noise and error, which is
required because millivolt level signals correspond to
amps of inductor current.
1. Place the capacitor Ccs2 close to the VO and
VCS pins of the IR3721. Treat VO and VCS as a
differential signal pair back to the IC as shown in
the elliptical area designated #1 of figure 8.
2. Sense the inductor (or shunt) Kelvin style at its
terminals. Route the leads back as a differential
pair. Refer to area #2 of figure 8.
5. Use an isolated dedicated ground plane
connected only to components associated with
the IR3721 that connect to GND as shown in
figure 9. Connect this dedicated ground plane at
one location only to the ground of the monitored
voltage. The thermally relived via in figure eight
illustrates this connection.
6. Bypass IC VDD pin 5 to GND pin 4 with a high
quality 0.1 μF ceramic capacitor. Refer to area #6
of figure 8.
7. Bypass the IC VK pin to GND with a high quality
0.1 μF ceramic capacitor. Refer to area #7 of
figure 8.
3. Route signal VOUT back to the IC VK pin on its
own dedicated trace. Refer to area #3 of figure 8.
4. Place the thermistor near the inductor. Refer to
area #4 of figure 8. Route the thermistor leads
back to the rest of the network using differential
traces. Mount the rest of the thermistor network
consisting of Rs, Rp, and R1 close to the IC.
L1
1
2
VOUT
VOUT
Ccs1
Rcs1
Ccs2
Rs
U1
Rcs2
1
2
3
4
5
10
9
8
7
6
CS
VO
RT
VCC_1
VK
R_DI_FILT
DI_FILT
DI
GND_1GND_3
VCC GND_4
IR3721
VDD
C_VDD
0.1uF
C_DI_FILT
Rth
R1
C_VK
0.1uF
Rp
GND
0
Figure 7 Example schematic
Page 11 of 16
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IR3721
DATA SHEET
2
3
4
1
7
6
Figure 8 Layer 1
Figure 10 Layer 3
Figure 9 Layer 2
Figure 11 Layer 4
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IR3721
DATA SHEET
PCB PAD AND COMPONENT PLACEMENT
Figure 12 below shows suggested pad and component placement.
Figure 12 Pad placement
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IR3721
DATA SHEET
SOLDER RESIST
Figure 13 below shows suggested solder resist placement.
Figure 13 Solder resist
Page 14 of 16
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IR3721
DATA SHEET
STENCIL DESIGN
Figure 14 below shows a suggested stencil design.
Figure 14 Stencil design
Page 15 of 16
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09/15/08
IR3721
DATA SHEET
PACKAGE INFORMATION
3 X 3 MM 10L DFN LEAD FREE
Data and specifications subject to change without notice.
This product has been designed and qualified for the Consumer market.
Qualification Standards can be found on IR’s Web site.
IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105
TAC Fax: (310) 252-7903
Visit us at www.irf.com for sales contact information.
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