SHT1x Humidity & Temperature Sensmitter _ Relative humidity and temperature sensors _ Dew point _ Fully calibrated, digital output _ No external components required _ Ultra low power consumption _ Surface mountable package _ Excellent long-term stability _ Small size _ Automatic power down Preliminary Information February 2002 SHT1x Product Summary The SHT1x is a single chip relative humidity and temperature multi sensor module comprising a calibrated digital output. Application of industrial CMOS processes with customized post processing (CMOSens™ technology) ensures highest reliability and excellent long term stability. The device includes two calibrated microsensors for relative humidity and temperature which are seamlessly coupled to a 14bit analog to digital converter and a serial interface circuit on the same chip. This results in superior signal quality, a fast response time and insensitivity to external disturbances (EMC) at a very competitive price. Each sensor is calibrated in a precision humidity chamber and the calibration coefficients are programmed into the OTP memory. These coefficients are used internally during measurements to calibrate the signals from the sensors. The 2-wire serial interface allows easy and fast system integration. Its tiny (7x5x3mm) size and low power consumption makes it the ultimate choice for even the most demanding applications including automotive, instrumentation, medical equipment, heating, ventilation and air conditioning systems (HVAC), portable consumer electronics and battery-operated controllers. The device is supplied in a surface-mountable LCC type package. Other packaging options are available on request. SHT1x Single Chip Relative Humidity and Temperature Sensor Module Calibration Memory %RH Sensor D t Amplification DATA i -b 14 Temp. Sensor SCK A Digital 2-wire Interface GND VDD Willow Technologies Limited, Shawlands Court, Newchapel Road, Lingfield, Surrey, RH7 6BL, UK Tel: + 44 (0)1342 835234 Fax: + 44 (0)1342 834306 SHT1x Relative Humidity & Temperature Sensor System 1 Sensor Performance Specifications(1) Parameter Humidity Resolution Conditions Min. Typ. Max. Units 0.5 0.03 0.03 8 12 12 ±0.1 see figure 1 Repeatability Accuracy(2) & Interchangeability Nonlinearity 10 - 90 %RH Range Response time 1/e (63%) 0 slowly moving air % RH % RH/yr ±1 <1 ± 5% ± 4% ± 3% ± 2% ± 1% ± 0% SHT11 SHT15 %RH 0% 10% 20% 30% 40% 50% 60% 70% 80% 90 % 100% ± 3°C 0.04 0.01 0.01 12 14 14 ±0.1 see figure 1 -40 123.8 20 °C bit °C °C °C s ± 2°C SHT15 0°C 0°C 40°C ± 1.8°F 80°C 100°C 120°C Dewpoint accuracy @25°C (typical) SHT11 SHT15 0°F ± 9.0°F ± 7.2°F ± 5.4°F ± 3.6°F ± 1.8°F 0% 10% 20% 30% 40% 50% 60% 70% 80% 90 % 100% Figure 1 Sensor Performance Specifications ± 3.6°F SHT11 ± 1°C ± 5°C ± 4°C ± 3°C ± 2°C ± 1°C ± 0°C ± 5.4°F Temperature accuracy -40°C% Repeatability Accuracy Range Response Time Table 1 % RH 100 % RH s ±3 4 Hysteresis Long term stability Typical Temperature Resolution % RH bit % RH % RH Absolute accuracy RH %RH RH, T, and Dewpoint accuracies 1.1 Converting the digital output to physical values 1.1.1 Humidity To compensate for the non-linearity of the humidity sensor and to obtain the full accuracy it is recommended to convert the readout with the following formula: RHlinear = c1 + c2 • SORH + c3 • SORH 2 where SORH is the sensor readout for RH and with c3 = -2.8 *10-6 for 12bit SORH c1 = -4 c2 = 0.0405 c1 = -4 c2 = 0.648 c3 = -7.2 *10-4 for 8bit SORH For simplified, less computation intense conversion formulas see application note “RH Non-Linearity Compensation”. 80% 60% %RH 20% (2) Not with t1 = 0.01; t2 = 0.00008, t2 = 0.00128 for 8bit SORH This equals ~1.2% per 10°C at 50%RH 1.1.2 Temperature The temperature sensor is very linear by design. Use the following formulas or table to convert from digital 14bit readout to temperature: Digital Readout 12 bit 14 bit 000 0000 FFF 3FFF 40% (1) For RH true = (T°C - 25) • (t 1 + t 2 • SORH ) + RHlinear T°c = SOT * 0.01 – 40 T°F = SOT * 0.018 – 40 where SOT is the 14bit sensor readout for Temperature. Multiply coefficient by 4 for 12 bit measurements. 100% 0% 0 For temperatures significantly different from 25°C (~77°F) the temperature coefficient of the RH sensor should be considered: 500 1000 1500 2000 2500 SORH sensor readout 3000 Temperature -40°C 123.83°C -40°F 254.89°F 1.1.3 Dewpoint See application note “Dewpoint calculation” for more information. operation within normal operation range as described in Chapter 3 including non-linearity Willow Technologies Limited, Shawlands Court, Newchapel Road, Lingfield, Surrey, RH7 6BL, UK Tel. + 44 (0)1342 835234 Fax. + 44 (0)1342 834306 SHT1x Relative Humidity & Temperature Sensor System 2 (See Figure 2). Pull-up resistors are often included in I/O circuits of microcontrollers Serial Interface Vdd GND uC (master) 1 2 3 4 DATA SCK SHT 1x (slave) Vdd 2.4 - 5.5V Figure 2 2.2.3 Command sequence To initiate a transmission a “Transmission Start” sequence has to be issued. It consists of a lowering of the DATA line while SCK is high, followed by a low pulse on SCK and raising DATA again while SCK is still high. Typical application circuit D AT A Pin 1 2 3 4 Name GND DATA SCK VDD Table 2 Comment Ground Serial data bidirectional Serial clock input Supply 2.4 – 5.5V SCK Figure 3 SHT1x Pin Description 2.1 Power Pins The SHT1x requires a voltage supply between 2.4V and 5.5V. After powerup the device requires 11ms to reach its “sleep” state. No commands should be sent before that time. Power supply pins (VDD, GND) may be decoupled with a 100 nF capacitor. 2.2 I/O Pins (Bidirectional 2-wire Interface) See Table 5 for a detailed IO characteristics. 2.2.1 Serial clock input (SCK) The SCK is used to synchronize the communication between a master and the SHT1x. 2.2.2 Serial data (DATA) The DATA tristate pin is used to transfer data in and out of the device. Data must be updated on this pin after the falling edge and is valid on the rising edge of the serial clock SCK. An external pull-up resistor is required to pull the signal high. Command Reserved Measure Temperature Measure Humidity Status Register Read Status Register Write Reserved Soft reset Table 3 Code 0000x 00011 00101 00111 00110 0101x-1110x 11110 "Transmission Start" sequence The subsequent command sequence consists of three address bits (only “000” is currently supported) and five command bits. The proper reception of a command by the SHT1x is indicated by pulling the ack bit low on the DATA pin. See 2.2.5 “Measurement Sequence” for an application of the command sequence 2.2.4 Connection reset sequence If communication with the SHT1x is lost the following signal sequence will reset its serial interface: While leaving DATA high toggle SCK 9 or more times. This must be followed by a “Transmission Start” sequence preceding the next command. DATA Transmission Start SCK Figure 4 1 2 3 4 -8 9 Connection reset sequence Description Reserved Temperature measurement Humidity measurement Read access to the status register (see application note) Write access to the status register (see application note) Reserved resets the chip, clears the status register to default values wait 11ms before next command SHT1x list of commands Adr MSB LSB Checksum ack 0 LSB ack 0 0 0 ack ack TS wait for data ready Command Willow Technologies Limited, Shawlands Court, Newchapel Road, Lingfield, Surrey, RH7 6BL, UK Tel. + 44 (0)1342 835234 Fax. + 44 (0)1342 834306 SHT1x Relative Humidity & Temperature Sensor System 2.2.5 Measurement sequence (T and RH) After issuing a measurement command (‘00000101’ for RH, ‘00000011’ for Temperature) the controller has to wait for the measurement to complete. This takes approximately 11/55/210ms for a 8/12/14bit measurement. The exact time varies by up to ±15% with the speed of the internal oscillator. To signal the completion of a measurement, the SHT1x pulls down the data line 2 and the controller must restart SCK. Two bytes of measurement data and one byte of CRC checksum will then be transmitted. The uC must acknowledge each byte by pulling the DATA line low. All values are MSB first, right justified. (e.g. the 5th SCK is MSB for a 12bit value). Communication terminates after the acknowledge bit of the Transmission Start Address=’000’ CRC data. If CRC-8 Checksum is not used the controller may terminate the communication after the measurement data LSB by keeping ack high. The SHT 11 automatically returns to sleep mode after the measurement and communication have finished. Warning: To keep heat up of the SHT1x below 0.1°C it should not be active for more than 15% of the time (e.g. max. 3 measurements / second for 12bit accuracy). 2.2.6 CRC-8 Checksum Calculation Please consult application note “CRC-8 Checksum Calculation” for information on how to calculate the CRC. Measurement ≈ 55ms for 12 bit ≈ 11ms for 8 bit Command=’00101’ DATA a2 a0 a1 C4 C3 C2 C1 C0 Bold = SHT1X controls DATA signal Normal = uC controls DATA line ack SCK After the sensor pulls down the DATA pin, measurement is ready for readout Skip acknowledge to end communication (if no CRC is needed) 12 bit humidity data DATA SCK 2 low low low low 11 10 9 8 ack 7 6 5 4 3 MSB Wait for next measurement DATA 6 5 4 3 2 1 0 SCK MSB Figure 5 1 0 ack LSB CRC-8 Checksum 7 2 ack Transmission Start Skip acknowledge to end communication. SHT 1x returns to sleep automatically LSB Example RH measurement sequence for value “0000’1101 ’ 0011’0001”= 3377 = 94.22%RH 2.3 Status Register Some of the advanced functions of the SHT1x are available through the status register. The following section gives a brief overview of these features. Please consult application note “Status Register” for more information. 2.3.1 Heater An on chip heating element can be switched on. It will increase the temperature of the sensor by approximately 5°C. Power consumption will increase by 8mA @ 5V. Applications: • By comparing temperature and humidity values before and after switching on the heater, proper functionality of both sensors can be verified. • In high RH environments heating the sensor element will avoid condensation. Warning: The built-in calibration is not correct while the SHT1x is heated! 2.3.2 End Of Life (EOL) The SHT1x End of Life (EOL) function detects VDD voltages below 2.5V. Accuracy is ±0.05V 2.3.3 Measurement resolution The default measurement resolution of 14bit (temperature) and 12bit (humidity) can be reduced to 12 and 8 bit. This is especially useful in high speed or extreme low power applications. Please consult application note “Status Register” for more information on how to access and use these features. Willow Technologies Limited, Shawlands Court, Newchapel Road, Lingfield, Surrey, RH7 6BL, UK Tel. + 44 (0)1342 835234 Fax. + 44 (0)1342 834306 SHT1x Relative Humidity & Temperature Sensor System 3 Specifications SHT1x 3.4 Electrical Specifications(1) 3.1 Absolute Maximum Ratings Ambient Storage Temperature: -40°C to 120°C 3.2 Operating Conditions 100% 80% 60% 40% 20% 0% -40°C Figure 6 Maximum operating conditions conditions 40°C 3.4.2 DC Characteristics VDD=5V, Temperature= 25°C unless otherwise noted Parameter Power supply DC Supply current Normal operating 0°C 3.4.1 ESD (Electrostatic Discharge) ESD immunity is qualified according to MIL STD 883E, method 3015 (Human Body Model at ±2kV)). Latch-up immunity is provided at a force current of ±100 mA with Tamb=80°C according to JEDEC 17. 80°C 100°C 120°C Recommended operating conditions Temperatures outside the recommended range may temporarily offset the RH signal by up to +3%RH. The sensor will slowly return to calibration conditions but heating the device up to 90°C at <5%RH for 24h will reverse the effect of high RH, high temperature environments promptly. Prolonged exposure to extreme conditions may accelerate ageing of the sensor. 3.3 Special Conditions Extensive tests were performed in various environments. Please contact us for complete qualification results. Min. Typ. 2.4 5 measuring 550 average 2(2) 28(3) sleep 0.3 Low level output voltage 0 High level output voltage 75% Low level input voltage Negative going 0 High level input voltage Positive going 80% Input current on pads Output peak current on Tristated (off) 10 Table 4 3.4.3 Conditions Max. Units 5.5 V µA µA 1 µA 20% Vdd 100% Vdd 20% Vdd 100% Vdd 1 µA 4 mA µA SHT1x DC Characteristics I/O Characteristics Parameter FSCK SCK frequency Conditions Min Typ. Max. VDD > 4.5 V 10 VDD < 4.5 V 1 TRFO DATA fall time Output load 5 pF 3.5 10 20 Output load 100 pF 30 40 200 TCLH SCK high time 100 TCLL SCK low time 100 TV DATA valid from 50 THO Output hold time 0 10 TR/TF SCK rise/fall time 200 Table 5 Unit MHz MHz ns ns ns ns ns ns ns SHT1x I/O Signals Characteristics TCLH TR TF FSCK SCK TV THO DATA Figure 7 (1) (2) (3) Timing Diagram Parameters are periodically sampled and not 100% tested With one measurement of 8 bit accuracy without OTP reload per second With one measurement of 12bit accuracy per second Willow Technologies Limited, Shawlands Court, Newchapel Road, Lingfield, Surrey, RH7 6BL, UK Tel. + 44 (0)1342 835234 Fax. + 44 (0)1342 834306 SHT1x Relative Humidity & Temperature Sensor System 4 Physical Dimensions and Mounting Information Prolonged direct exposure of the SHT1x to strong light or UV radiation should be avoided. 4.1 Package type The device is supplied in a surface-mountable LCC type package. The sensors housing consists of a Liquid Crystal Polymer (LCP) cap with epoxy glob top on a standard 0.8mm FR4 substrate. Device size is 7.62 x 5.08 x 2.5 mm. Weight 100mg Other packaging options are available on request. 4.3 Wiring considerations and signal integrity Carrying the SCK and DATA signal parallel an in close proximity (e.g. in wires) for more than 10cm may result in crosstalk and loss of communication. This may be resolved by routing VDD and/or GND between the two signals. 4.2 Mounting Recommendations 4.4 Soldering Information The relative humidity of a gas strongly depends on its temperature. It is therefore essential to keep the sensor at the same temperature as the air of which the humidity is to be measured. If the SHT1x shares a PCB with heating electronic components it should be mounted below the heat source and the housing must remain well ventilated. To reduce heat conduction copper layers between the SHT1x and the rest of the PCB should be minimized and a slit may be milled in between. The SHT1x can be soldered using standard reflow ovens at maximum 225°C for 20 seconds. For manual soldering contact time must be limited to 5 seconds at up to 350°C Please consult the application note “Soldering procedure” for detailed instructions. 4.5 Delivery Conditions The SHT1x will be delivered in standard IC tubes by max. 80 pieces per tube. Other delivery options may be available on request. Recommended PCB Footprint Top View 0.64 1.9 2.54 0.8 4 0.47 3 4.09 1.27 7.62 2 1.8 3.48 4.61 1 1.27 1.27 1.27 1.1 No Copper inside this field sensor opening 1.8 7.08 5.08 all measurements in mm Side View 2.5 actual size Willow Technologies Limited, Shawlands Court, Newchapel Road, Lingfield, Surrey, RH7 6BL, UK Tel. + 44 (0)1342 835234 Fax. + 44 (0)1342 834306 SHT1x Relative Humidity & Temperature Sensor System 5 IMPORTANT NOTICES The warranty for each product comes in the form of a written warranty which governs sale and use of such product. Such warranty is contained in the printed terms and conditions under which such product is sold, or in a separate written warranty supplied with the product. Please refer to such written warranty with respect to its applicability to certain applications of such product. These products may be subject to restrictions on use. Please contact SENSIRION AG for a list of the current additional restrictions on these products. By purchasing these products, the purchaser of these products agrees to comply with such restrictions. Please contact SENSIRION AG for clarification of any restrictions described herein. SENSIRION AG reserves the right, without further notice, to change the SENSIRION SHT1x Relative Humidity and Temperature Sensor product specifications and/or information in this document and to improve reliability, functions and design. SENSIRION AG assumes no responsibility or liability for any use of SENSIRION SHT1x product. Application examples and alternative uses of the SENSIRION SHT1x are for illustration purposes only and SENSIRION AG makes no representation or warranty that such applications shall be suitable for the use specified. Copyright 2001-2002, SENSIRION AG. All rights reserved. 6 Caution The inherent design of this component causes it to be sensitive to electrostatic discharge (ESD). To prevent ESDinduced damage and/or degradation, take normal ESD precautions when handling this product. Headquarters and Sales Office SENSIRION AG Eggbühlstr. 14 P.O. Box CH-8052 Zürich Switzerland www.sensirion.com Phone: + 41 (0)1 306 40 00 Fax: + 41 (0)1 306 40 30 e-mail: [email protected] http://www.sensirion.com/ February 2002 Preliminary Information 7/7