SMT172 ETC1 | Alldatasheet
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maart 20, 2017 reference V14 page Features and Highlights /circle6 World’s most energy efficient temperature sensor 0.36 µ J/measurement (T A=25° C, 3.3V) /circle6 Wide temperature range: -45° C to 130° C /circle6 Wide supply voltage range: 2.7V to 5.5V /circle6 High accuracy: ±0.25° C (-10° C to 100° C TO18) /circle6 Extreme low noise: 0.002° C /circle6 Ultra-low current (60µA active or 220nA average) /circle6 Excellent long term stability /circle6 Direct interface with Microcontroller (MCU) /circle6 Wide range of package options Application /circle6 Ultra-low power applications: wearable electronics , wireless sensor networks /circle6 Medical applications: body temperature monitoring /circle6 Instrumentation: (Bio)chemical analysis, precision equipment /circle6 Environmental monitoring (indoor/outdoor) /circle6 Industrial applications: process monitoring/contro lling Introduction The SMT172 is an ultra-low power, high-precision te mperature sensor that combines the ease of use with the world’s leading performance over a wide tempera ture 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 me thods, to achieve an absolute inaccuracy of less th an ±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 (0.36 µ J/measurement). The SMT172 has a pulse width modulated (PWM) output signal, where the duty cycle is proportional to th e measured temperature. This makes it possible that t he sensor can directly interface to a MCU without u sing an Analog-to-Digital Converter (ADC). Today, the ha rdware 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 fo r any user to get started with this sensor and achieve a very quick time to market.
maart 20, 2017 reference V14 page Specifications TA= -45° C to 130° C, Vcc=2.7V to 5.5V, unless otherwise noted. Parameter Min Typ Max Unit Conditions Supply Voltage 2.7 5.5 V Active current 1 50 µA T A = -45° C, Vcc = 2.7V, no load at the output pin 60 µA T A = 25° C, Vcc = 3.3V, no load at the output pin 70 µA T A = 25° C, Vcc = 5.5V, no load at the output pin Average current 220 nA T A = 25° C, Vcc = 3.3V, one measurement per second Power down current 0 µA When controlling with V cc pin Accuracy TO18 0.25 2 ° C -10 ° C to 100 ° C 0.82 ° C -45 ° C to 130 ° C 0.13 ° C -20 ° C to 80 ° C (second order interpretation) 0.43 ° C -45 ° C to 130 ° C (second order interpretation) Accuracy TO92/TO220 SOT223 0.35 2 ° C -10 ° C to 100 ° C 12 ° C -45 ° C to 130 ° C 0.25 2 ° C -20 ° C to 80 ° C (second order interpretation) 0.82 ° C -45 ° C to 130 ° C (second order interpretation) time of measurement 1.8 ms T A = 25° C, Vcc = 3.3V, 8 periods Noise 4 <0.0002 ° C T A = 25 ° C, Vcc = 5 V, 1 s measurement time Output Duty Cycle 0.11 0.93 -45° C to 130° C Output frequency 0.5 7 kHz 1 - 4 kHz for Vcc= 4.7 -5.5 V and TA=-25° C to 110° C PSRR at Vcc 0.1 ° C/V Repeatability 5 0.01 ° C T A = 25° C, Vcc = 5V, TO18 Startup time 1 2 ms after Vcc, start measurement on first negative edge Long term drift 0.0058 ° C T A = 22° C, Vcc = 5V, 365 days, TO18 Output impedance 100 Ω by design Operating Temperature -45 130 ° C Storage Temperature -50 150 ° C First order relation between Duty Cycle and temperature : T = 212.77 DC - 68.085 Second order relation between Duty cycle and temperature : T = -1.43 DC +214.56 DC - 68.6 1: Continuous conversion. 2: All error included, based on moving average of 80 valid duty cycles. 3: ±3 σ value. For this accuracy, second order interpretat ion 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 multipl e 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 m ultiple measurements on the same temperature point during multiple temperature cycles
maart 20, 2017 reference V14 page Absolute Maximum Rating TA=25° C. All voltages are referenced to GND, unless otherwise noted. Power supply voltage -0.5V to 7V Output pin load 50mA Operating temperature range -55° C1 to 135° C Storage temperature range -60° C to 150° C ESD protection (HBM) 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 sen sors have a duty cycle (PWM) output that can be dir ectly interfaced with a microcontroller without the use o f extra components. The output is a square wave wit h a well-defined temperature-dependent duty cycle. In g eneral, the duty cycle of the output signal is defi ned by a linear equation: /g2160/g2159 = /g2777./g2780/g2779+/g2777./g2777/g2777/g2781/g2783×/g2176 where DC = Valid Duty Cycle T = Temperature in ° C The temperature is derived from the measured duty cycle by: /g1836 = /g4005/g4003/g2879/g2868./g2871/g2870 /g2868./g2868/g2868/g2872/g2875 = 212.77×/g1840/g1829 −68.085 The frequency of the sensor output varies with the temperature and the supply voltage, but it does not contain temperature information. Only the duty cycl e contains temperature information in accordance to the formula given above. A higher accuracy can be achieved when a second ord er 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 th e average of individual duty cycles from 8 conseque nt output periods. This is due to the internal working principle of the SMT172 sensor. In order to elimin ate 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 t he averaged value of 8 consequent periods ( valid duty cycle ) is very stable and precise.
maart 20, 2017 reference V14 page Therefore, a valid duty cycle is: /g1840/g1829 = ∑ /g4005/g4003 /g4283 /g4123 /g4283/g4128/g4117 /g2876 /g1840/g1829 /g4046= /g4037/g4257/g4283 /g4037/g4261/g4283 /g2878/g4037/g4257/g4283 Where tHi = time interval of high state tLi = time interval of low state DC i = duty cycle of individual period i DC = the valid duty cycle The specified accuracy and noise performance are ba sed 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 deri ved that there is a fixed ratio between the frequen cy of the sensor output, the sampling rate and the sampling noise. The uncertainty of the temperature measurement is determined by: /g1836 /g4042/g4035/g4035 = 200 /g1872/g4036 /g43946/g1872/g4030/g1872/g4034 tp ts Note: The above mentioned error Terr is NOT related to the intrinsic accuracy of the se nsor. 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 th e SMT172 sensor. The lower limit of the noise is determined by the flicker noise of the sensor, wher e further averaging will no longer reduce it. So th e 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. Where Terr = measurement uncertainty of temperature (= standa rd deviation of the sampling noise) t s = microcontrollers sampling rate t p = period of the sensor output tm = total measurement time, an integer number of tp
maart 20, 2017 reference V14 page 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 r ecent measurements on the plastic versions TO92, SOIC, SO T223 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 condit ion. The measured hysteresis in a thermal cycle (TO -18 packaged samples) is less than ±0.02°C over the who le temperature range. Even at extreme condition (TO -18 samples heated up to 200°C for 48 hours), the dr ift is still less than ±0.05°C over the whole temperature range (-45°C to 130°C). At room temperature (22ºC), the out put drift is less than 5.8mK over 365 days. Typical Performance Characteristics Accuracy vs. Temperature (TO18 VCC =5V) Normalized Error vs. Supply Voltage Supply Current vs. Temperature Maximum Error Limit Maximum Error Limit SMT172 SMT172
maart 20, 2017 reference V14 page 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 i s 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: /g1836 = −1.43/g1840/g1829 /g2870+214.56/g1840/g1829 −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 Accuracy vs. temperature (V CC =5V, TO18)
Application Information
The SMT172 measures the temperature of its bipolar transistors with high precision. Due to the great SMT172 SMT172
maart 20, 2017 reference V14 page thermal conducting property of single crystalline s ilicon, we can assume the temperature difference wi thin the sensor die to be negligible. However the therma l property of the package material, the shape and t he 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 the rmal 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 me tals and thermal paste. When measuring air temperatures, it is important to isolate the sensor from the rest of the measurement system, so that t he heating from the surrounding circuit components has only a small influence on the sensor temperature. Self-Heating All electronic circuits consume power, and all powe r 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 influen ce 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. De sign 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 se nsor die. Depending on the packaging material and the immerging substances, this can vary in a wide r ange 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 In a bath filled with oil that is stirred constantly 1.4 In air that moves at 3m/s: - Without heat sink - With heat sink 13.5 In non-moving air: - Without heat sink - With heat sink 100
maart 20, 2017 reference V14 page 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 shoul d be a ceramic type and have a value of approximately 100nF. The location should be as close to the sens or as possible. The SMT172 has a very accurate output, the positive and negative edges of the output sign al are very steep, about 5ns. This means when using lo nger cables (over 30cm) there can be an effect of t he cable inductance and capacitance which means the pu lse is “reflected” and will give a spike on the sensors power supply line and the output of the sen sor. 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 th e V cc line a resistor of (R1) 100/1000 Ω . In case the cable capacitance is big and the edges disturbs the electronics in the device, an alternat ive solution is to put a series resistor of 100/500 Ω (R2) in the output line of the sensor. It must be realised this will cause the positive and negative edges to be le ss steep, so the accuracy of the measured temperatu re is influenced. In case the SMT172 is used as a repl acement of the SMT160 this accuracy problem will no t be an issue. This resistor can also damp the spikes on the signa l as well on the V cc line. The resistor in the Vcc line will also limit the maximum current in case of faults or wrong connections. Local electronics GND OUT SMT172 100nF VCC
maart 20, 2017 reference V14 page SOT SOT SOT SOT 223 223 223 223 Packaging SOIC -8L TO220 TO92 HEC TO18 Ordering code: SMT172-SOT223 SMT172 in SOT223 encapsulation SMT172 -TO18 SMT172 in TO -18 encapsulation SMT172-TO92 SMT172 in TO -92 encapsulation SMT172-TO220 SMT172 in TO -220 encapsulation SMT172 -SOIC SMT172 in SOIC -8 encapsulation SMT172-HEC SMT172 in HEC encapsulation SMT172-DIE SMT172 DIE (die size 1.7 x 1.3 mm) Related products: SMTAS04 evaluation board for 4 sensors input (RS232) SMTAS04USB evaluation board for 4 sensors input (USB connection) SMTAS08 evaluation board for 8 sensors input (RS232) SMTAS08USB evaluation board for 8 sensors input (USB connection) Pin 1 Vcc Pin 7 Gnd Pin 8 Out All sizes in mm
1 Output
3 GND
2.5 2.5 2.5 2.5 8.5 8.5 8.5 8.5 22 22 33 33 11 11 C 1 3 2 metal backplate = GND SMT172 xxxx 1 2 3 SM 172 xxxx Pin Pin Pin Pin 11 11 Pin Pin Pin Pin 55 55 6.1 3.85 5.08 0.41 1.27 1 2 3