ADT7401 SMBus/I2C Compatible, 0.5C Accurate 12-Bit Digital Temperature Sensor with Daisy Chain Preliminary Data Sheet (REV. PrE)
SMBus/I
2
C
Compatible, 0.5C Accurate 12-Bit
Digital Temperature Sensor with Daisy
Chain
Preliminary Technical Data
ADT7401
Rev. PrE
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703
2004 Analog Devices, Inc. All rights reserved.
FEATURES
12-Bit Temperature-to-Digital Converter
0.5C Accuracy at 25C
1C Accuracy from 0C to +70C
Operation from -40C to 150C
Operation from 2.7V to 5.5V
Power Consumption TBD mW Max at 5.5 V
Power Saving One Shot Mode
Pin Selectable Addressing via AS pin
Sub-SMBus/I
2
C Bus via DC pin
Small Low Cost 6-Pin SOT-23 Package and 8-Pin
MSOP
APPLICATIONS
Isolated Sensors
Environmental Control Systems
Refrigeration Systems
Thermal Protection
Industrial Process Control
Power System Monitors
Automotive
Medical
GENERAL DESCRIPTION
The ADT7401 is a complete temperature monitoring system
that outputs a 12-bit digital word corresponding to the temp-
erature of the ADT7401's silicon. The device offers a high
temperature accuracy of 1C from 0C to +70C, with
excellent transducer linearity. The digital output of the
ADT7401 is SMBus/I
2
C compatible.
The ADT7401 is specified for operation at supply voltages from
2.7 V to 5.5 V. Operating at 3.3 V the supply current is typically
230 A.
The ADT7401 is rated for operation over the -40C to +150C
temperature range. It is packaged in a low cost, low area SOT-23
package and mini-SOIC package. The SMBus ALERT pin is an
open-drain output that is used as an out of limit temperature
indicator. It can be wired-AND with other SMBus ALERT pins
and is used in conjunction with the SMBus General Call
Address.
The DC (Daisy Chain) pin creates a sub-SMBus/I
2
C bus where
a multiple of ADT7401's can be used. The DC pin has the
advantage of freeing up the address options on the root bus as
only one ADT7401 root address needs to be used by the
SMBus/I
2
C controller but still being able to address a number of
ADT7401 temperature sensors.
PRODUCT HIGHLIGHTS
1.
The ADT7401 has an on-chip temperature sensor that
allows an accurate measurement of the ambient
temperature. The measurable temperature range is -40C
to +150C.
2.
Supply voltage of 2.7 V to 5.5 V.
3.
Space-saving 6-lead SOT-23 package and 8-lead MSOP.
4.
Temperature accuracy of 0.5C.
5.
0.0625C temperature resolution.
6.
The ADT7401 features a one shot mode that reduces the
power consumption to 2.57 W at one sample per second.
FUNCTIONAL BLOCK DIAGRAM
Figure 1. SOT-23 Functional Block Diagram
ADT7401
Preliminary Technical Data
Rev. PrE | Page 2 of 12
TABLE OF CONTENTS
Specifications..................................................................................... 3
Timing Characteristics..................................................................... 4
Absolute Maximum Ratings............................................................ 5
ESD Caution.................................................................................. 5
Pin Configuration and Function Descriptions............................. 6
Typical Performance Curves ........................................................... 7
Circuit Information...................................................................... 9
Converter Details.......................................................................... 9
Application Hints ........................................................................... 10
Thermal Response Time ........................................................... 10
Self-Heating Effects.................................................................... 10
Supply Decoupling ..................................................................... 10
Temperature Monitoring........................................................... 10
Outline Dimensions ....................................................................... 11
Ordering Guide .......................................................................... 12
Preliminary Technical Data
ADT7401
Rev. PrE | Page 3 of 12
SPECIFICATIONS
All specifications apply for -40C to +150C unless otherwise stated. T
A
= T
MIN
to T
MAX
, V
DD
= +2.7 V to +5.5 V, unless otherwise noted
Table 1.
Parameter
Min
Typ
Max
Units
Test Conditions/Comments
TEMPERATURE SENSOR AND ADC
Accuracy @ V
DD
= +3.3 V (10%)
0.5
C
T
A
= 25C.
1
C
T
A
= 0C to 70C.
2
C
T
A
= -40C to +85C.
3
C
T
A
= -40C to +125C.
4
1
C
T
A
= -40C to +150C.
Accuracy @ V
DD
= +5 V (10%)
0.5
C
T
A
= 25C.
1
C
T
A
= 0C to 70C.
2
C
T
A
= -40C to +85C.
3
C
T
A
= -40C to +125C.
4
1
C
T
A
= -40C to +150C.
Temperature Resolution
0.0625
C
Equivalent to 12 Bits Sigma Delta ADC
Temperature Conversion Time
200
ms
Temperature Update Rtae
1
s
Time between each conversion
Long Term Drift
0.25
C
Drift over 10 years if part is operated at +55C.
Power Supply Rejection Ratio
0.3
0.6
C/V
T
A
= +25C
DIGITAL INPUTS
2
Input Current
1
A
V
IN
= 0 V to V
DD
V
IL
, Input Low Voltage
0.3V
DD
V
V
IH
, Input High Voltage
0.7V
DD
V
Pin Capacitance
3
10
pF
All digital inputs
SCL, SDA Glitch Rejection
50
ns
Input filtering suppresses noise spikes of less than 50 ns.
DIGITAL OUTPUTS
2
V
OH
, Ouput High Voltage
2.4
V
I
SOURCE
= I
SINK
= 200 A
V
OL
, Output Low Voltage
0.4
V
I
OL
= 3 mA
I
OH
, Output High Current
1
mA
V
OH
= 5 V
C
OUT
, Output Capacitance
50
p F
SUPPLIES
Supply Voltage
2.7
5.5
V
Supply Current
Serial Bus Inactive.
Normal Mode
6
@ 3.3 V
230
450
A
Device Converting.
Normal Mode
6
@ 5 V
300
500
A
Device Converting.
Quiescent
6
@ 3.3 V
3
8
A
Device not converting.
Quiescent
6
@ 5.5 V
5
10
A
Device not converting.
One Shot Mode @ 1 sps
21.16
A
Average Current @ V
DD
= 2.7 V to 3.6 V.
One Shot Mode @ 1 sps
28.6
A
Average Current @ V
DD
= 4.5 V to 5.5 V.
Shutdown Current
0.3
1
A
Power Dissipation
759
W
V
DD
= +3.3 V, Continuously Converting
Power Dissipation
1 sps
69.83
W
Average Power Dissipated for
V
DD
= +3.3 V. One Shot Mode.
1 sps
143
W
Average Power Dissipated for
V
DD
= +5 V. One Shot Mode.
1
It is not recommended to operate the device at temperatures above +125C for greater than a total of 5% of the lifetime of the device. Any exposure beyond this limit
will affect device reliability.
2
Guaranteed by design and characterization, not production tested.
ADT7401
Preliminary Technical Data
Rev. PrE | Page 4 of 12
TIMING CHARACTERISTICS
Guaranteed by design and characterization, not production tested. The SDA & SCL timing is measured with the input filters turned on so
as to meet the Fast-Mode I
2
C specification. Switching off the input filters improves the transfer rate but has a negative affect on the EMC
behaviour of the part. T
A
= T
MIN
to T
MAX
, V
DD
= +2.7 V to +5.5 V, unless otherwise noted.
Table 2.
Parameter
Limit
Units
Comments
Serial Clock Period, t
1
2.5
s
Fast Mode I
2
C. See Figure 2
Data In Setup Time to SCL High, t
2
50
ns
Data Out Stable after SCL Low, t
3
0
ns
See Figure 2
SDA Low Setup Time to SCL Low
(Start Condition), t
4
50
ns
See Figure 2
SDA High Hold Time after SCL High
(Stop Condition), t
5
50
ns
See Figure 2
SDA and SCL Fall Time, t
6
90
ns
See Figure 2
Figure 2. SMBus/I
2
C Timing Diagram
Figure 3. Load Circuit for Access Time and Bus Relinquish Time
Preliminary Technical Data
ADT7401
Rev. PrE | Page 5 of 12
ABSOLUTE MAXIMUM RATINGS
Table 3.
Parameter Rating
V
DD
to GND
0.3 V to +7 V
Digital Input Voltage to GND
0.3 V to V
DD
+ 0.3 V
Maximum Output Current (OUT)
10 mA
Operating Temperature Range
3
40C to +150C
Storage Temperature Range
65C to +160C
Max Junction Temperature, T
JMAX
+150C
6-Lead SOT-23
Power Dissipation
4
W
MAX
= (T
JMAX
- T
A
5
)/
JA
Thermal Impedance
6
JA
, Junction-to-Ambient
(still air)
229.6C/W
JC
, Junction-to-Case
91.99C/W
8-Lead MSOP (RM-8)
Power Dissipation
2
W
MAX
= (T
JMAX
- T
A
3
)/
JA
Thermal Impedance
4
JA
, Junction-to-Ambient
(still air)
205.9C/W
JC
, Junction-to-Case
43.74C/W
IR Reflow Soldering
Peak Temperature
+220C (-0/+5C)
Time at Peak Temperature
10 to 20 secs
Ramp-up Rate
2-3C/sec
Ramp-down Rate
6C/sec
3
It is not recommended to operate the device at temperatures above +125C
for greater than a total of 5% of the lifetime of the device. Any exposure
beyond this limit will affect device reliability.
4
Values relate to the package being used on a 2-layer PCB. See
. for a
plot of max power dissipation vs. ambient temperature (T
Figure 4
A
).
5
T
A
= Ambient Temperature.
6
Junction-to-Case resistance is applicable to components featuring a
preferential flow direction, e.g. components mounted on a heat sink.
Junction-to-Ambient resistance is more useful for air-cooled PCB mounted
components.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Figure 4. Plot of Maximum Power Dissipation vs. Temperature
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
ADT7401
Preliminary Technical Data
Rev. PrE | Page 6 of 12
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Figure 5. Pin Configurations
Table 4. Pin Function Description
Mnemonic
SOT-23
Pin No.
MSOP
Pin No.
Description
SDA
6
1
SMBus/I
2
C Serial Data Input/Output. Open-drain configuration needs a pullup resistor.
SCL
5
2
Serial clock input. Open-drain configuration.
ALERT
4
3
Digital open-drain output. Out of limit temperature indicator. This output becomes active when
temperature exceeds T
HIGH
or T
LOW
limits. Can be programmed to be active low or active high
GND
3
4
Analog and Digital Ground.
DC
2
7
Daisy Chain Digital Input/Output. This pin acts as the input/output conduit for the sub-SMBus/I
2
C
bus. Push-Pull configuration.
V
DD
1
8
Positive Supply Voltage, 2.7 V to 5.5 V.
A0
-
5
Digital Input. User set programmable bit of the serial bus address.
A1
-
6
Digital Input. User set programmable bit of the serial bus address.
Preliminary Technical Data
ADT7401
Rev. PrE | Page 7 of 12
TYPICAL PERFORMANCE CURVES
Figure 6. Supply Current vs. Supply Voltage @ +25C
Figure 7. Shutdown Current vs. Supply Voltage @ +25C
Figure 8. PSRR vs. Supply Ripple Frequency
Figure 9. Temperature Error at 3.3 V and 5 V
ADT7401
Preliminary Technical Data
Rev. PrE | Page 8 of 12
Figure 10. Temperature Error vs. Power Supply Noise Frequency
Figure 11. Temperature Sensor Response to Thermal Shock
Figure 12. Supply Current vs. Temperature
Figure 13. Power Supply Rejection vs. Temperature
Preliminary Technical Data
ADT7401
Rev. PrE | Page 9 of 12
CIRCUIT INFORMATION
The ADT7401 is a standalone temperature sensor that generates
a 12-bit digital output in two's complement that varies in direct
proportion with the temperature of the device. An onboard
sensor generates a voltage precisely proportional to absolute
temperature which is compared to an internal voltage reference
and input to a precision digital modulator. The serial digital
output is converted into a 12-bit digital word and stored in the
Temperature Value Register. Overall accuracy is 5C from 0C
to +70C, with excellent transducer linearity. The digital output
of the ADT7401 is SMBus/I
2
C compatible, and is easily
interfaced to most popular microcontrollers.
The onboard temperature sensor has excellent accuracy and
linearity over the entire rated temperature range without
correction or calibration by the user.
The sensor output is digitized by a first-order sigma-delta
modulator, also known as the "charge balance" type analog-to-
digital converter. This type of converter utilizes time-domain
oversampling and a high accuracy comparator to deliver 12 bits
of effective accuracy in an extremely compact circuit.
CONVERTER DETAILS
The sigma-delta modulator consists of an input sampler, a
summing network, an integrator, a comparator, and a 1-bit
DAC. Similar to the voltage-to-frequency converter, this
architecture creates in effect a negative feedback loop whose
intent is to minimize the integrator output by changing the duty
cycle of the comparator output in response to input voltage
changes. The comparator samples the output of the integrator at
a much higher rate than the input sampling frequency, this is
called oversampling. This spreads the quantization noise over a
much wider band than that of the input signal, improving
overall noise performance and increasing accuracy.
Figure 14. First-Order Sigma-Delta Modulator
The modulated output of the comparator is encoded using a
circuit technique, which results in a serial digital signal. This
signal is then converted into a 12-bit digital word for storage
into a register. The final output format is two's complement.
ADT7401
Preliminary Technical Data
Rev. PrE | Page 10 of 12
APPLICATION HINTS
THERMAL RESPONSE TIME
The time required for a temperature sensor to settle to a
specified accuracy is a function of the thermal mass of, and the
thermal conductivity between, the sensor and the object being
sensed. Thermal mass is often considered equivalent to
capacitance. Thermal conductivity is commonly specified using
the symbol , and can be thought of as thermal resistance. It is
commonly specified in units of degrees per watt of power
transferred across the thermal joint. Thus, the time required for
the ADT7401 to settle to the desired accuracy is dependent on
the package, the thermal contact established in that particular
application, and the equivalent power of the heat source. In
most applications, the settling time is probably best determined
empirically.
SELF-HEATING EFFECTS
The temperature measurement accuracy of the ADT7401 may
be degraded in some applications due to self-heating. Errors
introduced are from the quiescent dissipation and power
dissipated when converting. The magnitude of these
temperature errors is dependent on the thermal conductivity of
the ADT7401 package, the mounting technique, and effects of
airflow. Static dissipation in the ADT7401 is typically 10 W
operating at 3.3 V with no load. In the 6 lead SOT-23 package
mounted in free air, this accounts for a temperature increase
due to self-heating of:
C
W
C
W
P
T
JA
DISS
=
=
=
0328
.
0
/
6
.
229
143
It is recommended that current dissipated through the device is
kept to a minimum as it has a proportional affect on the
temperature error.
SUPPLY DECOUPLING
The ADT7401 should be decoupled with a 0.1 F ceramic
capacitor between V
DD
and GND. This is particularly important
if the ADT7401 is mounted remote from the power supply.
Precision analog products, such as the ADT7401, require a well
filtered power source. Since the ADT7401 operates from a
single supply, it seems convenient to simply tap into the digital
logic power supply. Unfortunately, the logic supply is often a
switch-mode design, which generates noise in the 20 kHz to 1
MHz range. In addition, fast logic gates can generate glitches
hundred of millivolts in amplitude due to wiring resistance and
inductance.
If possible, the ADT7401 should be powered directly from the
system power supply. This arrangement, shown in Figure 15,
will isolate the analog section from the logic switching
transients. Even if a separate power supply trace is not available,
however, generous supply bypassing will reduce supply-line
induced errors. Local supply bypassing consisting of a 0.1 F
ceramic capacitor is recommended.
Figure 15. Use Separate Traces to Reduce Power Supply Noise
TEMPERATURE MONITORING
The ADT7401 is ideal for monitoring the thermal environment
within electronic equipment. For example, the surface mounted
package will accurately reflect the exact thermal conditions
which affect nearby integrated circuits.
The ADT7401 measures and converts the temperature at the
surface of their own semiconductor chip. When the ADT7401 is
used to measure the temperature of a nearby heat source, the
thermal impedance between the heat source and the ADT7401
must be considered. Often, a thermocouple or other
temperature sensor is used to measure the temperature of the
source while the ADT7401's temperature is monitored. Once
the thermal impedance is determined, the temperature of the
heat source can be inferred from the ADT7401 output.
One example of using the ADT7401's unique properties is in
monitoring a high power dissipation microprocessor. The
adt7401, in a surface mount package, is mounted directly
beneath the microprocessor's pin grid array (PGA) package.
Preliminary Technical Data
ADT7401
Rev. PrE | Page 11 of 12
OUTLINE DIMENSIONS
Figure 16. 6-Lead Plastic Surface Mount SOT-23
RT-6)
Dimensions shown in Millimeters
Figure 17. 8-Lead Plastic Surface Mount Mini/Micro SOIC (MSOP)
(RM-8)
Dimensions shown in Millimeters
ADT7401
Preliminary Technical Data
Rev. PrE | Page 12 of 12
ORDERING GUIDE
Model
Temperature
Range
1
Temperature
Accuracy
2
Package
Description
Branding
Information
Package
Option
Minimum
Quantities/Reel
ADT7401RT-
500REEL7
-40C to +150C
1C
6-Lead SOT-23
RJ-6
500
ADT7401RT-REEL -40C to +150C
1C
6-Lead SOT-23
RJ-6
10000
ADT7401RT-
REEL7
-40C to +150C
1C
6-Lead SOT-23
RJ-6
3000
ADT7401RM-
500REEL7
-40C to +150C
1C
8-Lead MSOP
RM-8
500
ADT7401RM-
REEL
-40C to +150C
1C
8-Lead MSOP
RM-8
10000
ADT7401RM-
REEL7
-40C to +150C
1C
8-Lead MSOP
RM-8
3000
Purchase of licensed I
2
C components of Analog Devices or one of its sublicensed Associated Companies conveys a license for the
purchaser under the Philips I
2
C Patent Rights to use these components in an I
2
C system, provided that the system conforms to the I
2
C
Standard Specification as defined by Philips.
1
It is not recommended to operate the device at temperatures above +125C for greater than a total of 5% of the lifetime of the device. Any exposure beyond this limit
will affect device reliability.
2
Temperature accuracy is over 0C to +70C temperature range.
2004 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective companies.
PR04792-0-3/04(PrE)
Document Outline
PDF 
ZIP