FM50 — Analog Temperature Sensor
April 2008
FM50 — Analog Temperature Sensor
Features
Analog Output: 10mV/°C
Range: -40 to 125°C Range
Accuracy: ±2°C at 25°C
Supply Current: 170μA Maximum
Output Drive: 25μA
Self-heating: <0.1°C
Operating Voltage: +2.4V to +6V
Description
As a precision CMOS temperature sensor, the FM50 is
cost effective for accurate, low-power, temperature-
monitoring applications. Output voltage versus
temperature is extremely linear. With no load, the
supply current is typically 130µA. For normal operation,
the load on V
OUT
should be 100KΩ or less.
In a typical application, a remotely mounted FM50 is
monitored by a microcontroller with an analog A/D
converter input. Alternatively, the FM50 can drive a
comparator with a high-impedance input.
Accuracy is typically ±0.5°C at room temperature, and
better than ±2°C from 0 to 75°C.
FM50 is available in a 3-pin SOT-23 package.
Applications
Mobile Phones
Computers
Battery Management
Office Equipment
HVAC
Power Supply Modules
Disk Drives
Automotive
Ordering Information
Part Number
FM50S3X
Operating Temperature Range
-40 to +125°C
Package
3-Pin SOT-23
Packing Method
3000 Units, Tape and Reel
All packages are lead free per JEDEC: J-STD-020B standard.
Figure 1. Output Voltage vs. Temperature
© 2004 Fairchild Semiconductor Corporation
FM50 • Rev. 1.1.1
www.fairchildsemi.com
FM50 — Analog Temperature Sensor
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device
reliability. The absolute maximum ratings are stress ratings only.
Symbol
V
DD
V
OUT
I
OUT
T
J
T
STG
T
L
ESD
Parameter
Supply Voltage
Output Voltage
Output Current
Operating Temperature Range
Storage Temperature Range
Lead Soldering Temperature
Human Body Model, JESD22-A114
Machine Model, JESD22-A115
(2)
(1)
Min.
Max.
+7
V
DD
+0.5
10
Unit
V
V
µA
°C
°C
°C
V
-50
-60
+150
+150
+220
2000
250
Notes:
1. Human body model: 100pF capacitor discharged through a t 1.5kW resister into each pin.
2. Machine model: 200pF capacitor discharged directly into each pin.
Electrical Characteristics
Limits apply for -40°C
≤
T
A
≤
+125°C and V
DD
=+5.0V unless otherwise noted. These specifications are guaranteed
only for the test conditions listed.
Symbol
A
OUT
Parameter
Sensitivity
Output at 25°C
Conditions
Min.
9.7
740
Typ.
10.0
750
±0.5
±1.0
±1
Max.
10.3
760
+2.0
+3.5
+3
+125
+0.8
1750
Units
mV/°C
mV
°C
°C
°C
mV
µA
mA
µA
Transfer Characteristics
T
A
=+25°C
Accuracy
T
A
Output
V
OUT
I
ONSN
I
ONSG
I
OL
R
OUT
R
LOAD
Power
V
DD
I
Q
Package
Θ
JA
Thermal Resistance
Supply Voltage
Quiescent Current
No Output Load
Output Voltage Range
Output Current Source
Output Current Sink
Output Resistance
Load Regulation
100kΩ Load at 25°C
Sensing
Surge
(3)
-2.0
-3.5
-3
-40
-0.8
100
T
A
=-40°C (T
MIN
)
T
A
=+125°C (T
MAX
)
Temperature Range
Non-Linearity
(4)
25
50
1
10
kΩ
mV/mA
2.4
6.0
170
260
V
µA
°C/W
Notes:
3. Accuracy (expressed in °C)= difference between calculated output voltage and measured output voltage.
Calculated output voltage =10m/V°C multiplied by the device’s case temperature at specific conditions of
temperature, voltage and power supply, added to 500mV.
4. Non-linearity is defined as the deviation of the output voltage vs. temperature curve from the best fit straight line
over the rated temperature range.
© 2004 Fairchild Semiconductor Corporation
FM50 • Rev. 1.1.1
www.fairchildsemi.com
3
FM50 — Analog Temperature Sensor
Functional Description
The FM50 contains a thermal diode, calibration
circuits, and amplifiers. Since the FM50 is calibrated
at 33°C, the nominal output in mV is:
V
OUT
= 830 + 10 • (T-33)
where T is the
expressed in °C.
thermal
junction
(1)
temperature
Thermal
Delay Errors
For measurement accuracy of the order of tenths of
1°C, adequate settling time must be allowed. For a
typical circuit board installation, 15 minutes should be
allowed to elapse after reading temperature within
1~2°C of the expected final value. Once V
OUT
has
ceased to slew and is stable (with or without about
±0.1°C noise) for about five minutes, temperature can
be calculated
.
At 33°C, the tolerances are:
Offset is ±3mV.
Slope is ±0.3mV/°C.
These values accommodate the specified accuracies
at -40, +25, and +125°C.
Output structure is an N-channel CMOS transistor
driving a P-channel load. Available current is typically
50μA to ground. Series resistance is typically 7kΩ,
charging and 2kΩ, discharging through a capacitor
connected from V
OUT
to ground.
Following application of power to V
DD
, V
OUT
is
accurate after a delay of approximately 80ms.
Location Errors
Position is source of error. Even within a controlled
thermal environment, changing location by a few
inches can lead to errors of several tenths of 1°C.
Mounting
The FM50 can be easily mounted by gluing or
cementing it to a surface. In this case, its temperature
will be within about 0.2°C of the temperature of the
surface to which it is attached 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 die will be at an intermediate
temperature between the surface temperature and
the air temperature.
To ensure good thermal conductivity, the backside of
the die is directly attached to the GND pin. The lands
and traces to the FM50 are part of the printed circuit
board, for which the temperature is being measured.
These printed circuit board lands and traces do not
cause the FM50’s temperature to deviate from the
desired temperature.
Alternatively, the FM50 can be mounted inside a
sealed-end metal tube and can be dipped into a bath
or screwed into a threaded hole in a tank. As with any
IC, the FM50 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
FM50 or it connections.
Application Information
Although the FM50 is a simple device, care must be
taken to ensure that temperature is measured
accurately. The major sources of errors are:
Voltage Errors
Thermal Delay Errors
Location Errors
Voltage Errors
Figure 6. Recommended Electrical Connections
A Kelvin connection is recommended to avoid errors
due to voltage drops in the ground connections.
Although the typical 130μA supply current draw only
causes a 130μV error; if the series resistance is 1Ω, a
100mA current supply to adjacent circuits can cause
a 10mV drop across 100mΩ (10mΩ is a typical value
for soldered joints or contact resistance), leading to a
1°C error. For this reason, the FM50 should be Kelvin
connected, as shown in Figure 6.
© 2004 Fairchild Semiconductor Corporation
FM50 • Rev. 1.1.1
www.fairchildsemi.com
5
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