SMT172-SOT223 [ETC]
World most energy efficient temperature sensor;
| 型号： | SMT172-SOT223 |
| 厂家： | 
ETC |
| 描述： | World most energy efficient temperature sensor |
| 文件： | 总9页 (文件大小：807K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
last update
maart 20, 2017
reference
V14
DATASHEET
SMT172
page
1/9
Features and Highlights
ꢀ
World’s most energy efficient temperature sensor
0.36µJ/measurement (TA=25°C, 3.3V)
Wide temperature range: -45°C to 130°C
Wide supply voltage range: 2.7V to 5.5V
High accuracy: 0.25°C (-10°C to 100°C TO18)
0.1°C (-20°C to 60°C, TO18)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Extreme low noise: 0.002°C
Ultra-low current (60µA active or 220nA average)
Excellent long term stability
Direct interface with Microcontroller (MCU)
Wide range of package options
Application
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Ultra-low power applications: wearable electronics, wireless sensor networks
Medical applications: body temperature monitoring
Instrumentation: (Bio)chemical analysis, precision equipment
Environmental monitoring (indoor/outdoor)
Industrial applications: process monitoring/controlling
Introduction
The SMT172 is an ultra-low power, high-precision temperature sensor that combines the ease of use with
the world’s leading performance over a wide temperature range. Using the most recent advances in the
silicon temperature sensing technology, the SMT172 has applied some really sophisticated IC design
techniques as well as high-precision calibration methods, to achieve an absolute inaccuracy of less than
0.1°C in the range of -20°C to 60°C
The SMT172 operates with a supply voltage from 2.7V to 5.5V. The typical active current of only 60µA, the
high speed conversion over 4000 outputs per second (at room temperature) and an extremely low noise
makes this sensor the most energy efficient temperature sensor in the world (0.36µJ/measurement).
The SMT172 has a pulse width modulated (PWM) output signal, where the duty cycle is proportional to the
measured temperature. This makes it possible that the sensor can directly interface to a MCU without using
an Analog-to-Digital Converter (ADC). Today, the hardware Timer in a MCU to read our PWM signal has
become available almost universally, fast in speed and low in cost. Therefore, it is extremely easy for any
user to get started with this sensor and achieve a very quick time to market.
last update
maart 20, 2017
DATASHEET
SMT172
reference
V14
page
2
Specifications
TA= -45°C to 130°C, Vcc=2.7V to 5.5V, unless otherwise noted.
Parameter
Supply Voltage
Min
Typ
Max
Unit
V
Conditions
2.7
5.5
50
60
µA
µA
µA
nA
µA
°C
°C
°C
°C
°C
°C
°C
°C
ms
°C
TA = -45°C, Vcc = 2.7V, no load at the output pin
TA = 25°C, Vcc = 3.3V, no load at the output pin
TA = 25°C, Vcc = 5.5V, no load at the output pin
Active current1
70
Average current
220
TA = 25°C, Vcc = 3.3V, one measurement per second
When controlling with Vcc pin
Power down current
0
2
-10 °C to 100 °C
0.25
2
-45 °C to 130 °C
0.8
0.1
0.4
Accuracy TO18
3
3
-20 °C to 80 °C (second order interpretation)
-45 °C to 130 °C (second order interpretation)
-10 °C to 100 °C
2
0.35
2
1
-45 °C to 130 °C
Accuracy TO92/TO220
SOT223
2
-20 °C to 80 °C (second order interpretation)
-45 °C to 130 °C (second order interpretation)
TA = 25°C, Vcc = 3.3V, 8 periods
TA = 25 °C, Vcc = 5 V, 1 s measurement time
-45°C to 130°C
0.25
2
0.8
time of measurement
Noise4
1.8
<0.0002
0.93
7
Output Duty Cycle
Output frequency
PSRR at Vcc
0.11
0.5
kHz
°C/V
°C
1 - 4 kHz for Vcc= 4.7-5.5 V and TA=-25°C to 110°C
0.1
Repeatability5
0.01
2
TA = 25°C, Vcc = 5V, TO18
Startup time
1
ms
°C
after Vcc, start measurement on first negative edge
TA = 22°C, Vcc = 5V, 365 days, TO18
by design
Long term drift
0.0058
100
130
150
Output impedance
Operating Temperature
Storage Temperature
ꢀ
-45
-50
°C
°C
T = 212.77 DC - 68.085
First order relation between Duty Cycle and temperature
:
Second order relation between Duty cycle and temperature
:
T = -1.43 DC2 +214.56 DC - 68.6
1: Continuous conversion.
2: All error included, based on moving average of 80 valid duty cycles.
3
:
3σ value. For this accuracy, second order interpretation between Duty Cycle and temperature is used,
where a valid Duty Cycle is based on the averaged value of 8 successive periods.
4: Noise level will be reduced by averaging multiple consecutive measurements. For instance, noise can be
reduced to 0.0004°C and 0.0002 °C by taking average in 0.1s and 1s, respectively. Measurement time
should always be provided when noise is mentioned. The lower limit of the noise is determined by the
flicker noise of the sensor, where further averaging will no longer reduce the noise.
5: Repeatability is defined as difference between multiple measurements on the same temperature point
during multiple temperature cycles.
last update
maart 20, 2017
DATASHEET
SMT172
reference
V14
page
3
Absolute Maximum Rating
TA=25°C. All voltages are referenced to GND, unless otherwise noted.
-0.5V to 7V
Power supply voltage
Output pin load
50mA
Operating temperature range
Storage temperature range
ESD protection (HBM)
-55°C1 to 135°C
-60°C to 150°C
2000V
Junction temperature
200°C
Soldering temperature (SOIC, SOT)
260°C (10s)
1: For the accuracy over the temperature range from -55°C to -45°C and from 130°C to 135°C, contact
Smartec BV.
Output Signal
According to tradition, the Smartec temperature sensors have a duty cycle (PWM) output that can be directly
interfaced with a microcontroller without the use of extra components. The output is a square wave with a
well-defined temperature-dependent duty cycle. In general, the duty cycle of the output signal is defined by a
linear equation:
ꢀꢁ = ꢂ. ꢃꢄ + ꢂ. ꢂꢂꢅꢆ × ꢇ
where
DC = Valid Duty Cycle
T = Temperature in °C
A simple calculation shows that, i.e. at 0°C, DC=0.32 (32%); at 130°C, DC=0.931 (93.1%).
The temperature is derived from the measured duty cycle by:
ꢈ = ꢉꢊꢋꢌ.ꢍꢎ = 212.77 × ꢑꢒꢓ − 68.085
ꢌ.ꢌꢌꢏꢐ
The frequency of the sensor output varies with the temperature and the supply voltage, but it does not
contain temperature information. Only the duty cycle contains temperature information in accordance to the
formula given above.
A higher accuracy can be achieved when a second order formula is used, an accuracy of 0.1°C can be
achieved in the range of -20°C to 60°C.
Valid Duty Cycle
A valid duty cycle in equation (1) is defined as the average of individual duty cycles from 8 consequent
output periods. This is due to the internal working principle of the SMT172 sensor. In order to eliminate the
error caused by component mismatching, DEM (Dynamic Element Matching) has been applied in SMT172. A
complete DEM cycle consists 8 periods. There might be large variation between each individual period, and
this variation changes from sensor to sensor, but the averaged value of 8 consequent periods (valid duty
cycle) is very stable and precise.
last update
maart 20, 2017
DATASHEET
SMT172
reference
V14
page
4
ꢕ
ꢑꢒ = ∑
ꢉꢊ
ꢔ
ꢔꢖꢗ
Therefore, a valid duty cycle is:
ꢘ
ꢚ
ꢛꢔ
ꢓꢑꢒꢙ = ꢚ
Where
tHi = time interval of high state
ꢝꢚ
ꢜꢔ ꢛꢔ
tLi = time interval of low state
DCi = duty cycle of individual period i
DC = the valid duty cycle
The specified accuracy and noise performance are based on a measurement of 8 periods. For improved
noise performance, measurement of multiples (N times) of 8 periods is recommended.
In other words:
After each period the duty cycle has to be calculated and stored. The mean duty cycle has to be taken over 8
periods or a multiple of 8 periods. This mean duty cycle is used to calculate the temperature.
Measurement always starts on the negative edge of the output signal.
Understanding the specifications
Sampling Noise
From the theory of signal processing it can be derived that there is a fixed ratio between the frequency of the
sensor output, the sampling rate and the sampling noise. The uncertainty of the temperature measurement is
determined by:
tp
ꢠꢡ
ꢈ
ꢞꢟꢟ
= 200
6ꢠ ꢠ
ꢣ
ꢢ
ꢤ
ts
Where T = measurement uncertainty of temperature (= standard deviation of the sampling
noise)
err
ts = microcontrollers sampling rate
tp = period of the sensor output
tm = total measurement time, an integer number of tp
Note:
The above mentioned error Terr is NOT related to the intrinsic accuracy of the sensor. It just indicates how
the uncertainty (standard deviation) is influenced when a microcontroller samples a time signal.
Sensor noise
Each semiconductor product generates noise, also the SMT172 sensor. The lower limit of the noise is
determined by the flicker noise of the sensor, where further averaging will no longer reduce it. So the
measured noise of the sensor of course depends on the measurement time. The noise of the sensor is
about 0.002°C when measuring over 3.6ms (8 periods, 5V). When measuring over about 0.1s the sensor
noise is reduced to 0.0004°C.
last update
maart 20, 2017
DATASHEET
SMT172
reference
V14
page
5
Package induced error
When applying high stress package materials, extra errors will occur and therefore system designers
should be aware of this effect. The TO-18 package has the minimum package induced errors. All other
packages can have a slightly bigger error on top of the error in the specifications but based on the recent
measurements on the plastic versions TO92, SOIC, SOT223 and TO220 the error will be less than
±0.35°C (-10°C to 100°C) and ±1°C over the temperature range of -45°C to 130°C.
Long-term drift
This drift strongly depends on the operating condition. The measured hysteresis in a thermal cycle (TO-18
packaged samples) is less than ±0.02°C over the whole temperature range. Even at extreme condition
(TO-18 samples heated up to 200°C for 48 hours), the drift is still less than ±0.05°C over the whole
temperature range (-45°C to 130°C). At room temperature (22ºC), the output drift is less than 5.8mK over
365 days.
Typical Performance Characteristics
SMT172
Maximum Error Limit
SMT172
Maximum Error Limit
Accuracy vs. Temperature (TO18 VCC=5V)
Normalized Error vs. Supply Voltage
Supply Current vs. Temperature
last update
maart 20, 2017
DATASHEET
SMT172
reference
V14
page
6
Measurement with improved accuracy
This part of the datasheet of the SMT172 provides information how a temperature can be measured with a
higher accuracy than what is specified in the datasheet.
How about
There are two reasons why the accuracy of ±0.25°C (-10°C to 100°C) has been specified in SMT172:
1. A linear equation, which is compatible with SMT160 has been used for duty cycle versus
temperature. Higher order system errors remain.
2. Due to the special design skill, one complete measurement is the average of 8 periods (or a
multiple of 8 periods). The specified accuracy in the datasheet is valid for all kinds of averaging
methods.
If a more accurate measurement is required, a more sophisticated interpretation of the output signal is
needed.
The better accuracy can only be achieved when:
1. Equation (2) is applied to obtain the valid duty cycle,
2. A second order equation is applied to translate the valid duty cycle to a temperature:
ꢈ = −1.43ꢑꢒꢎ + 214.56ꢑꢒ − 68.60
This second order equation can better interpret the valid duty cycle to temperature, and thus a more
accurate result can be achieved. The equation corrects for the typical error curve versus the temperature
as in the graph on the previous page.
Performance characteristic
SMT172
SMT172
Accuracy vs. temperature (VCC=5V, TO18)
Application Information
Temperature measurement
The SMT172 measures the temperature of its bipolar transistors with high precision. Due to the great
last update
maart 20, 2017
DATASHEET
SMT172
reference
V14
page
7
thermal conducting property of single crystalline silicon, we can assume the temperature difference within
the sensor die to be negligible. However the thermal property of the package material, the shape and the
size of soldering pads, the neighbouring components on the PCB as well as the presence of dedicated
thermal sinks are all affecting the die temperature that the sensor is measuring. Therefore a good thermal
path between the die and the object under measurement should be carefully designed and considered.
When measuring temperature of solid or liquid targets, it helps to have a good thermal contact between the
sensor and the target. This can be achieved with metals and thermal paste. When measuring air
temperatures, it is important to isolate the sensor from the rest of the measurement system, so that the
heating from the surrounding circuit components has only a small influence on the sensor temperature.
Self-Heating
All electronic circuits consume power, and all power becomes heat. Depending on the thermal resistance
to the environment and the related thermal mass on the heat path, this heat will cause an extra
temperature rise of the sensor die and will influence the final reading. Although the ultra-low power
consumption of SMT172 sensor minimizes this effect greatly, it is always important to take this into account
when designing a temperature measurement system. Design considerations like optimal thermal contact
with the environment and powering down the sensors whenever possible (see SMTAS08) are all useful
techniques to minimize this effect.
Thermal response time
The thermal response time of the temperature sensor is determined by both the thermal conductance and
the thermal mass between the heat source and the sensor die. Depending on the packaging material and
the immerging substances, this can vary in a wide range from sub-second to hundreds of seconds. The
following table illustrates the time constant (the time required to reach 63% of an instantaneous
temperature change) of TO-18 packaged sensors.
Conditions of installation
Time constant (s)
(TO-18)
In an aluminium block
0.6
1.4
In a bath filled with oil that is stirred
constantly
In air that moves at 3m/s:
-
-
Without heat sink
With heat sink
13.5
5
In non-moving air:
-
-
Without heat sink
With heat sink
60
100
last update
maart 20, 2017
DATASHEET
SMT172
reference
V14
page
8
Supply voltage decoupling/cable compensation.
It is common practice for precision analogue ICs to use a decoupling capacitor between Vcc and GND
pins. This capacitor ensures a better overall EMI/EMC performance. When applied, this capacitor should
be a ceramic type and have a value of approximately 100nF. The location should be as close to the sensor
as possible. The SMT172 has a very accurate output, the positive and negative edges of the output signal
are very steep, about 5ns. This means when using longer cables (over 30cm) there can be an effect of the
cable inductance and capacitance which means the pulse is “reflected” and will give a spike on the
sensors power supply line and the output of the sensor. These spikes can damage the electronics behind
this and also the sensor. Therefor we also advise (for longer cable) the user to put in series with the Vcc
line a resistor of (R1) 100/1000Ω.
In case the cable capacitance is big and the edges disturbs the electronics in the device, an alternative
solution is to put a series resistor of 100/500Ω (R2) in the output line of the sensor. It must be realised this
will cause the positive and negative edges to be less steep, so the accuracy of the measured temperature
is influenced. In case the SMT172 is used as a replacement of the SMT160 this accuracy problem will not
be an issue.
This resistor can also damp the spikes on the signal as well on the Vcc line. The resistor in the Vcc line
will also limit the maximum current in case of faults or wrong connections.
R2
1
OUT
R1
2
SMT172
VCC
100nF
3
GND
Local electronics
last update
maart 20, 2017
DATASHEET
SMT172
reference
V14
page
9
Packaging
SOIC-8L
TO220
TO92
5.08
Pin 1
Pin 1 Vcc
Pin 7 Gnd
SMT172
xxxx
3.85 6.1
SM172
xxxx
iOut
All sizes in mm
0.41
1.27
Pin 5
1 2 3
1 3 2
metal backplate = GND
HEC
TO18
1 Output
2 + Vcc
3 GND
2
2.5
3
2
C
1
8.5
3
bottom view
SOT223
Ordering code:
SMT172-SOT223
SMT172-TO18
SMT172-TO92
SMT172-TO220
SMT172-SOIC
SMT172-HEC
SMT172-DIE
SMT172 in SOT223 encapsulation
SMT172 in TO-18 encapsulation
SMT172 in TO-92 encapsulation
SMT172 in TO-220 encapsulation
SMT172 in SOIC-8 encapsulation
SMT172 in HEC encapsulation
SMT172 DIE (die size 1.7 x 1.3 mm)
SMT172
1
2
3
1
2
3
Vcc
Gnd/heatsink
Out
Related products:
SMTAS04
evaluation board for 4 sensors input (RS232)
SMTAS04USB
SMTAS08
evaluation board for 4 sensors input (USB connection)
evaluation board for 8 sensors input (RS232)
SMTAS08USB
evaluation board for 8 sensors input (USB connection)
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