Karta katalogowa DS18B20, Pierdoły, jakaś praca inż

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//-->LEAVAILABDS18B20Programmable Resolution1-Wire Digital ThermometerThe DS18B20 digital thermometer provides 9-bitto 12-bit Celsius temperature measurements andhas an alarm function with nonvolatile user-programmable upper and lower trigger points.The DS18B20 communicates over a 1-Wire busthat by definition requires only one data line (andground) for communication with a centralmicroprocessor. It has an operating temperaturerange of -55°C to +125°C and is accurate to±0.5°Cover the range of -10°C to +85°C. Inaddition, the DS18B20 can derive power directlyfrom the data line (“parasite power”), eliminatingthe need for an external power supply.Each DS18B20 has a unique 64-bit serial code,which allows multiple DS18B20s to function onthe same 1-Wire bus. Thus, it is simple to use onemicroprocessor to control many DS18B20sdistributed over a large area. Applications thatcan benefit from this feature include HVACenvironmental controls, temperature monitoringsystems inside buildings, equipment, ormachinery, and process monitoring and controlsystems.Functional DiagramsDESCRIPTIONUser-Definable Nonvolatile (NV) AlarmSettingsAlarm Search Command Identifies andAddresses Devices Whose Temperature isOutside Programmed Limits (TemperatureAlarm Condition)Available in 8-Pin SO (150 mils), 8-PinµSOP,and 3-Pin TO-92 PackagesSoftware Compatible with the DS1822Applications Include Thermostatic Controls,Industrial Systems, Consumer Products,Thermometers, or Any Thermally SensitiveSystemPIN CONFIGURATIONSMAXIM18B201 2 3N.C.N.C.VDDDQ18N.C.N.C.N.C.GNDMAXIM18B20234765SO (150 mils)(DS18B20Z)FEATURESUnique 1-Wire® Interface Requires Only OnePort Pin for CommunicationEach Device has a Unique 64-Bit Serial CodeStored in an On-Board ROMMultidrop Capability Simplifies DistributedTemperature-Sensing ApplicationsRequires No External ComponentsCan Be Powered from Data Line; Power SupplyRange is 3.0V to 5.5VMeasures Temperatures from -55°C to +125°C(-67°F to +257°F)±0.5°CAccuracy from -10°C to +85°CThermometerappear at endUser SelectablePin ConfigurationsResolution isof data sheet.from 9Diagrams continued at end of data sheet.Functionalto 12 BitsConverts TemperatureIntegratedDigital Word inUCSP is a trademark of Maximto 12-BitProducts, Inc.750ms (Max)GNDDQVDDDQN.C.N.C.GND12348765VDDN.C.N.C.N.C.1 2 3(BOTTOM VIEW)µSOP(DS18B20U)18B20TO-92(DS18B20)1-Wire is a registered trademark of Maxim Integrated Products, Inc.For pricing, delivery, and ordering information, please contact Maxim Directat 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.REV: 042208DS18B20ORDERING INFORMATIONPARTDS18B20DS18B20+DS18B20/T&RDS18B20+T&RDS18B20-SL/T&RDS18B20-SL+T&RDS18B20UDS18B20U+DS18B20U/T&RDS18B20U+T&RDS18B20ZDS18B20Z+DS18B20Z/T&RDS18B20Z+T&RTEMP RANGE-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°C-55°C to +125°CPIN-PACKAGE3 TO-923 TO-923 TO-92 (2000 Piece)3 TO-92 (2000 Piece)3 TO-92 (2000 Piece)*3 TO-92 (2000 Piece)*8µSOP8µSOP8µSOP(3000 Piece)8µSOP(3000 Piece)8 SO8 SO8 SO (2500 Piece)8 SO (2500 Piece)TOP MARK18B2018B2018B2018B2018B2018B2018B2018B2018B2018B20DS18B20DS18B20DS18B20DS18B20+Denotesa lead-free package. A “+” will appear on the top mark of lead-free packages.T&R = Tape and reel.*TO-92 packages in tape and reel can be ordered with straight or formed leads. Choose “SL” for straight leads. Bulk TO-92 orders are straightleads only.PIN DESCRIPTIONPINSO1, 2, 6,7, 8345µSOP2, 3, 5,6, 7814TO-92—321NAMEN.C.VDDDQGNDNo ConnectionOptional VDD. VDDmust be grounded for operation inparasite power mode.Data Input/Output. Open-drain 1-Wire interface pin. Alsoprovides power to the device when used in parasite powermode (see thePowering the DS18B20section.)GroundFUNCTIONFigure 1 shows a block diagram of the DS18B20, and pin descriptions are given in thePin Descriptiontable. The 64-bit ROM stores the device’s unique serial code. The scratchpad memory contains the 2-bytetemperature register that stores the digital output from the temperature sensor. In addition, the scratchpadprovides access to the 1-byte upper and lower alarm trigger registers (THand TL) and the 1-byteconfiguration register. The configuration register allows the user to set the resolution of the temperature-to-digital conversion to 9, 10, 11, or 12 bits. The TH, TL, and configuration registers are nonvolatile(EEPROM), so they will retain data when the device is powered down.The DS18B20 uses Maxim’s exclusive 1-Wire bus protocol that implements bus communication usingone control signal. The control line requires a weak pullup resistor since all devices are linked to the busvia a 3-state or open-drain port (the DQ pin in the case of the DS18B20). In this bus system, themicroprocessor (the master device) identifies and addresses devices on the bus using each device’s unique64-bit code. Because each device has a unique code, the number of devices that can be addressed on one2 of 22OVERVIEWDS18B20bus is virtually unlimited. The 1-Wire bus protocol, including detailed explanations of the commands and“time slots,” is covered in the1-Wire Bus Systemsection.Another feature of the DS18B20 is the ability to operate without an external power supply. Power isinstead supplied through the 1-Wire pullup resistor via the DQ pin when the bus is high. The high bussignal also charges an internal capacitor (CPP), which then supplies power to the device when the bus islow. This method of deriving power from the 1-Wire bus is referred to as “parasite power.” As analternative, the DS18B20 may also be powered by an external supply on VDD.Figure 1. DS18B20 Block DiagramVPU4.7kPARASITE POWERCIRCUITMEMORY CONTROLLOGICDS18B20TEMPERATURE SENSORDQINTERNAL VDD64-BIT ROMAND1-Wire PORTALARM HIGH TRIGGER (TH)REGISTER (EEPROM)ALARM LOW TRIGGER (TL)REGISTER (EEPROM)POWER-SUPPLYSENSECONFIGURATION REGISTER(EEPROM)8-BIT CRC GENERATORGNDCPPSCRATCHPADVDDThe core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of thetemperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C,0.25°C, 0.125°C, and 0.0625°C, respectively. The default resolution at power-up is 12-bit. The DS18B20powers up in a low-power idle state. To initiate a temperature measurement and A-to-D conversion, themaster must issue a Convert T [44h] command. Following the conversion, the resulting thermal data isstored in the 2-byte temperature register in the scratchpad memory and the DS18B20 returns to its idlestate. If the DS18B20 is powered by an external supply, the master can issue “read time slots” (see the1-Wire Bus Systemsection) after the Convert T command and the DS18B20 will respond by transmitting0 while the temperature conversion is in progress and 1 when the conversion is done. If the DS18B20 ispowered with parasite power, this notification technique cannot be used since the bus must be pulled highby a strong pullup during the entire temperature conversion. The bus requirements for parasite power areexplained in detail in thePowering the DS18B20section.The DS18B20 output temperature data is calibrated in degrees Celsius; for Fahrenheit applications, alookup table or conversion routine must be used. The temperature data is stored as a 16-bit sign-extendedtwo’s complement number in the temperature register (see Figure 2). The sign bits (S) indicate if thetemperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If theDS18B20 is configured for 12-bit resolution, all bits in the temperature register will contain valid data.For 11-bit resolution, bit 0 is undefined. For 10-bit resolution, bits 1 and 0 are undefined, and for 9-bitresolution bits 2, 1, and 0 are undefined. Table 1 gives examples of digital output data and thecorresponding temperature reading for 12-bit resolution conversions.3 of 22OPERATION—MEASURING TEMPERATUREDS18B20Figure 2. Temperature Register FormatBIT 732BIT 15MS BYTES = SIGNLS BYTEBIT 622BIT 14SBIT 521BIT 13SBIT 42BIT 12SBIT 32-1BIT 11SBIT 22-2BIT 1026BIT 12-3BIT 925BIT 02-4BIT 824STable 1. Temperature/Data RelationshipTEMPERATURE (°C)+125+85*+25.0625+10.125+0.5-0.5-10.125-25.0625-55DIGITAL OUTPUT(BINARY)0000 0111 1101 00000000 0101 0101 00000000 0001 1001 00010000 0000 1010 00100000 0000 0000 10000000 0000 0000 00001111 1111 1111 10001111 1111 0101 11101111 1110 0110 11111111 1100 1001 0000DIGITAL OUTPUT(HEX)07D0h0550h0191h00A2h0008h0000hFFF8hFF5EhFE6FhFC90h*Thepower-on reset value of the temperature register is +85°C.After the DS18B20 performs a temperature conversion, the temperature value is compared to the user-defined two’s complement alarm trigger values stored in the 1-byte THand TLregisters (see Figure 3).The sign bit (S) indicates if the value is positive or negative: for positive numbers S = 0 and for negativenumbers S = 1. The THand TLregisters are nonvolatile (EEPROM) so they will retain data when thedevice is powered down. THand TLcan be accessed through bytes 2 and 3 of the scratchpad as explainedin theMemorysection.Figure 3. THand TLRegister FormatBIT 7SBIT 626BIT 525BIT 424BIT 323BIT 222BIT 121BIT 02OPERATION—ALARM SIGNALINGOnly bits 11 through 4 of the temperature register are used in the THand TLcomparison since THand TLare 8-bit registers. If the measured temperature is lower than or equal to TLor higher than or equal to TH,an alarm condition exists and an alarm flag is set inside the DS18B20. This flag is updated after everytemperature measurement; therefore, if the alarm condition goes away, the flag will be turned off after thenext temperature conversion.4 of 22DS18B20The master device can check the alarm flag status of all DS18B20s on the bus by issuing an Alarm Search[ECh] command. Any DS18B20s with a set alarm flag will respond to the command, so the master candetermine exactly which DS18B20s have experienced an alarm condition. If an alarm condition existsand the THor TLsettings have changed, another temperature conversion should be done to validate thealarm condition.POWERING THE DS18B20The DS18B20 can be powered by an external supply on the VDDpin, or it can operate in “parasite power”mode, which allows the DS18B20 to function without a local external supply. Parasite power is veryuseful for applications that require remote temperature sensing or that are very space constrained.Figure 1 shows the DS18B20’s parasite-power control circuitry, which “steals” power from the 1-Wirebus via the DQ pin when the bus is high. The stolen charge powers the DS18B20 while the bus is high,and some of the charge is stored on the parasite power capacitor (CPP) to provide power when the bus islow. When the DS18B20 is used in parasite power mode, the VDDpin must be connected to ground.In parasite power mode, the 1-Wire bus and CPPcan provide sufficient current to the DS18B20 for mostoperations as long as the specified timing and voltage requirements are met (see theDC ElectricalCharacteristicsandAC Electrical Characteristics).However, when the DS18B20 is performingtemperature conversions or copying data from the scratchpad memory to EEPROM, the operating currentcan be as high as 1.5mA. This current can cause an unacceptable voltage drop across the weak 1-Wirepullup resistor and is more current than can be supplied by CPP. To assure that the DS18B20 has sufficientsupply current, it is necessary to provide a strong pullup on the 1-Wire bus whenever temperatureconversions are taking place or data is being copied from the scratchpad to EEPROM. This can beaccomplished by using a MOSFET to pull the bus directly to the rail as shown in Figure 4. The 1-Wirebus must be switched to the strong pullup within 10µs (max) after a Convert T [44h] or Copy Scratchpad[48h] command is issued, and the bus must be held high by the pullup for the duration of the conversion(tCONV) or data transfer (tWR= 10ms). No other activity can take place on the 1-Wire bus while the pullupis enabled.The DS18B20 can also be powered by the conventional method of connecting an external power supplyto the VDDpin, as shown in Figure 5. The advantage of this method is that the MOSFET pullup is notrequired, and the 1-Wire bus is free to carry other traffic during the temperature conversion time.The use of parasite power is not recommended for temperatures above +100°C since the DS18B20 maynot be able to sustain communications due to the higher leakage currents that can exist at thesetemperatures. For applications in which such temperatures are likely, it is strongly recommended that theDS18B20 be powered by an external power supply.In some situations the bus master may not know whether the DS18B20s on the bus are parasite poweredor powered by external supplies. The master needs this information to determine if the strong bus pullupshould be used during temperature conversions. To get this information, the master can issue a Skip ROM[CCh] command followed by a Read Power Supply [B4h] command followed by a “read time slot”.During the read time slot, parasite powered DS18B20s will pull the bus low, and externally poweredDS18B20s will let the bus remain high. If the bus is pulled low, the master knows that it must supply thestrong pullup on the 1-Wire bus during temperature conversions.5 of 22 [ Pobierz całość w formacie PDF ]
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