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1-100707-01 Folha de dados(PDF) 5 Page - Sensitron |
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1-100707-01 Folha de dados(HTML) 5 Page - Sensitron |
5 / 12 page Datasheet SHT21 www.sensirion.com Version 1.0 – January 2010 5/12 Figure 8 Top view of example of mounted SHT2x with slits milled into PCB to minimize heat transfer. 2.5 Light The SHT2x is not light sensitive. Prolonged direct exposure to sunshine or strong UV radiation may age the sensor. 2.6 Materials Used for Sealing / Mounting Many materials absorb humidity and will act as a buffer increasing response times and hysteresis. Materials in the vicinity of the sensor must therefore be carefully chosen. Recommended materials are: Any metals, LCP, POM (Delrin), PTFE (Teflon), PEEK, PP, PB, PPS, PSU, PVDF, PVF. For sealing and gluing (use sparingly): Use high filled epoxy for electronic packaging (e.g. glob top, underfill), and Silicone. Out-gassing of these materials may also contaminate the sensor (see Section 1.3). Therefore try to add the sensor as a last manufacturing step to the assembly, store the assembly well ventilated after manufacturing or bake at >50°C for 24h to outgas contaminants before packing. 2.7 Wiring Considerations and Signal Integrity Carrying the SCL and SDA signal parallel and in close proximity (e.g. in wires) for more than 10cm may result in cross talk and loss of communication. This may be resolved by routing VDD and/or VSS between the two SDA signals and/or using shielded cables. Furthermore, slowing down SCL frequency will possibly improve signal integrity. Power supply pins (VDD, VSS) must be decoupled with a 100nF capacitor – see next Section. 3 Interface Specifications Pin Name Comment 2 VSS Ground 1 SDA Serial Data, bidirectional 6 SCL Serial Clock, bidirectional 5 VDD Supply Voltage 3,4 NC Not Connected, floating Table 2 SHT2x pin assignment, NC remain floating 3.1 Power Pins (VDD, VSS) The supply voltage of SHT2x must be in the range of 2.1 – 3.6V, recommended supply voltage is 3.0V. Power supply pins Supply Voltage (VDD) and Ground (VSS) must be decoupled with a 100nF capacitor, that shall be placed as close to the sensor as possible – see Figure 9. 3.2 Serial clock (SCL) SCL is used to synchronize the communication between microcontroller (MCU) and the sensor. Since the interface consists of fully static logic there is no minimum SCL frequency. 3.3 Serial SDA (SDA) The SDA pin is used to transfer data in and out of the sensor. For sending a command to the sensor, SDA is valid on the rising edge of SCL and must remain stable while SCL is high. After the falling edge of SCL the SDA value may be changed. For safe communication SDA shall be valid tSU and tHD before the rising and after the falling edge of SCL, respectively – see Figure 10. For reading data from the sensor, SDA is valid tVD after SCL has gone low and remains valid until the next falling edge of SCL. Figure 9 Typical application circuit, including pull-up resistors RP and decoupling of VDD and VSS by a capacitor. To avoid signal contention the micro-controller unit (MCU) must only drive SDA and SCL low. External pull-up resistors (e.g. 10kΩ), are required to pull the signal high. For the choice of resistor size please take bus capacity requirements into account (compare Table 5). It should be noted that pull-up resistors may be included in I/O circuits SDA SCL GND VDD MCU (master) RP RP SCL OUT SDA OUT SDA IN SCL IN SHT2x (slave) 1 6 5 2 4 3 |
Nº de peça semelhante - 1-100707-01 |
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Descrição semelhante - 1-100707-01 |
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