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HERMISTOR
aSM121
New Release Specification
General Description
The aSM121 is a high-precision, 3-lead CMOS silicon
thermistor in an ultra-small leadless package that provides
a cost-effective solution for applications requiring high-
accuracy low-power temperature monitoring. The aSM121
functions in a way that is similar to a PTC thermistor.
However, it is linear-calibrated, enabling application
developers to directly interpret output voltage as
temperature without complex compensation for non-
linearity.
The aSM121 output voltage ramp has a positive slope of
10mV/°C that is independent of supply voltage. The
aSM121 has a guaranteed room temperature (25°C)
accuracy of ±1°C. The aSM121 does not require external
calibration - each device is calibrated at the factory.
P
RODUCT
S
PECIFICATION
Pin Configuration
QFN-3
V
DD
1
3
GND
aSM121
V
OUT
2
Features
•
•
•
•
•
•
•
•
•
Precision Calibrated to ±1°C at 25°C
Temperature Range: -30°C to 125°C
Extremely Linear Output Ramp: 10mV/°C
0°C Output: 0.50V
Output Ramp is Calibrated to Degrees Celsius
Low Operating Current: 14μA
Operating Voltage Range: +2.7 V to +3.6V
Non-linearity:
≤
0.8°C
1.2mm x 1.5mm QFN Package
4
3
Top view, contacts underneath,
actual part marking below
Accuracy vs Temperature
Accuracy (°C)
Applications
•
•
•
•
•
•
•
•
•
Mobile Phones
Mobile Communications Terminals
Computers
Battery Management
FAX Machines/Printers/Copiers
Portable Medical Instruments
HVAC, Power Supply Modules
Disk Drives
Automotive Control Circuits
2
1
0
-
-1
-
-2
-
-3
-4
-40
-20
0
20
25
upper spec limits
lower spec limits
125
40
60
80
100 120
Temperature (°C)
Ordering Information
Part Number
aSM121Q3
m – month / year code
Package
3-Lead QFN
Temperature Range
-30˚C to +125˚C
www.andigilog.com
Part Marking
Jm
How Supplied
3000 units on T&R
July 2005 - 70A04006
© Andigilog, Inc. 2004
aSM121
Absolute Maximum Ratings
1
Parameter
Supply Voltage
Output Voltage
Continuous Current, any terminal
Storage Temperature Range
ESD
2
Thermal
Resistance -
Θ
JA
Lead Temp
Human Body Model
Machine Model
QFN-3
Rating
+7V
V
DD
+ 0.5V
10mA
-60°C to +150°C
4000V
400V
TBD
260°C
Notes:
1. Absolute maximum ratings are limits beyond
which operation may cause permanent damage to
the device. These are stress ratings only;
functional operations at or above these limits is
not implied.
2. Human Body Model: 100pF capacitor discharged
through a 1.5kΩ resistor into each pin. Machine
Model: 200pF capacitor discharged directly into
each pin.
3. These specifications are guaranteed only for the
test conditions listed.
Recommended Operating Ratings
Symbol
V
DD
V
OUT
T
A
Parameter
Supply Voltage
Output Voltage
Operating Temperature Range
Min
+2.7
0
-30
Max
+3.6
1.8
+125
Units
V
V
°C
Electrical Characteristics
3
Limits apply for -40°C
≤
T
A
≤
+125°C and V
D D
= + 3 .0V unless otherwise noted.
Parameter
Accuracy
4
Symbol
Conditions
T
A
=+25°C
T
A
=-30°C (T
MIN
)
T
A
=+125°C (T
MAX
)
T
A
=+25°C
-30°C
≤
T
A
≤
+125°C
+2.7V < V
DD
< +3.6V
+2.7V < V
DD
< +3.6V
Min
-1
-4
-3
Typ
±0.5
±1
±1
±0.8
14
Max
+1
+4
+3
Units
°C
°C
°C
°C
Non-linearity
5
Supply Current - Output floating
Output Sink Capability
6
Output Source Capability
6
Average Output Slope
(Sensor Gain)
Zero-Degree Output Voltage
Room Temp Output Voltage
Self Heating
7
I
DD
I
OL
I
OH
A
OUT
V
OUT0
V
OUT25
15
—
25
200
10
μA
μA
μA
mV/°C
mV
mV
°C
T
A
=+0°C
T
A
=+25°C
QFN-3
500
750
0.025
Notes:
4. Accuracy (expressed in °C) = Difference between calculated output voltage and measured output voltage.
Calculated output voltage = 10mV/°C multiplied by device’s case temperature at specified conditions of temperature,
voltage and power supply with an offset of 500mV (see Fig. 1).
5. Non-linearity is defined as the deviation of the output-voltage-versus-temperature curve from the best-fit straight
line, over the device’s rated temperature range.
6. Lowest output current should be targeted; higher currents result in more self-heating of the device.
7. Max Self Heating =
Θ
JA
x (V
DD
x I
DD
). Assumes a capacitive load.
-2-
www.andigilog.com
© Andigilog, Inc. 2004
July 2005 - 70A04006
aSM121
V
OUT
(mV)
1750
1500
1350
900
750
500
300
200
-30
0
25
50
75
100
125
Temperature (ºC)
Temp (ºC) = (V
OUT
– 500mV) / 10mV/ºC)
Figure 1. aSM121 Output Voltage vs. Temperature
whose temperature is being measured. These printed
circuit board lands and traces will not cause the
aSM121’s temperature to deviate from the desired
temperature.
Alternatively, the aSM121 can be mounted inside a
sealed-end metal tube, and can then be dipped into a
bath or screwed into a threaded hole in a tank. As
with any IC, the aSM121 and accompanying wiring
and circuits must be kept insulated and dry to avoid
leakage and corrosion. This is especially true if the
circuit may operate at cold temperatures where
condensation can occur. Printed-circuit coatings and
varnishes such as Humiseal and epoxy paint or dips
can be used to ensure that moisture cannot corrode
the aSM121 or its connections.
Mounting
The aSM121 package provides good thermal
conductivity to the surface to which it is soldered. It’s
low mass allows it to respond quickly to changes in
board temperature. In this case, its temperature will be
within about 0.02°C of the temperature of the surface it
is attached to if the ambient air temperature is almost
the same as the surface temperature. If the air
temperature is much higher or lower than the surface
temperature, the actual temperature of the aSM121
die will be at an intermediate temperature between the
surface temperature and the air temperature.
To ensure good thermal conductivity, the backside of
the aSM121 die is directly attached to the GND pin.
The lands and traces to the aSM121 will, of course, be
part of the printed circuit board, which is the object
© Andigilog, Inc. 2004
-3-
www.andigilog.com
July 2005 - 70A04006
aSM121
Typical Performance Characteristics
16
15
14
13
12
I
DD
(µA)
11
10
9
8
7
-50
-25
0
25
50
50
75
V
DD
=+3V
100
125
Temperature (°C)
Figure 2. aSM121 Current vs Temperature
Typical Applications
3.3V
3.9K
V
Temp
IN
aSM121
U1
Serial
REF Analog-to-Digital
Converter
1.75V
+
FB
Adjustable
Shunt Voltage
Reference
U2
U3
SERIAL
DATA OUT
100K
CLOCK
10K
ENABLE
Figure 3. Serial Output Temperature to Digital Converter (Full Scale = +125˚C)
© Andigilog, Inc. 2004
-4-
www.andigilog.com
July 2005 - 70A04006
aSM121
Typical Applications (cont.)
3.3V
15K
aSM121
U1
_
U2
5K
+
1.75V
IN
8
PARALLEL
DATA
OUTPUT
Parallel Output
Analog-to-Digital
Converter
V
REF
INTR
U3
CS
15K
RD
WR
Figure 4. Parallel Output Temperature to Digital Converter (Full Scale = +125˚C)
3.3
R3
R4
2.5V
Shunt
Voltage
Reference
R1
V
T
+
U1
0.1μF
R2
–
V
OUT
U3
3.3
aSM121
U2
V
Temp
Figure 5. Thermostat / Fan Controller
© Andigilog, Inc. 2004
-5-
www.andigilog.com
July 2005 - 70A04006
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