Data Sheet

ManualsBrandsSparkfun Electronics Manualstemperature & humidity sensorsDS18B20 Waterproof Temperature Sensor

1 of 27 050400

FEATURES

 Unique 1-Wire interface requires only one

port pin for communication

 Multidrop capability simplifies distributed

temperature sensing applications

 Requires no external components

 Can be powered from data line. Power supply

range is 3.0V to 5.5V

 Zero standby power required

 Measures temperatures from -55°C to

+125°C. Fahrenheit equivalent is -67°F to

+257°F

 ±0.5°C accuracy from -10°C to +85°C

 Thermometer resolution is programmable

from 9 to 12 bits

 Converts 12-bit temperature to digital word in

750 ms (max.)

 User-definable, nonvolatile temperature alarm

settings

 Alarm search command identifies and

addresses devices whose temperature is

outside of programmed limits (temperature

alarm condition)

 Applications include thermostatic controls,

industrial systems, consumer products,

thermometers, or any thermally sensitive

system

PIN ASSIGNMENT

PIN DESCRIPTION

GND - Ground

DQ - Data In/Out

- Power Supply Voltage

NC - No Connect

DESCRIPTION

The DS18B20 Digital Thermometer provides 9 to 12-bit (configurable) temperature readings which

indicate the temperature of the device.

Information is sent to/from the DS18B20 over a 1-Wire interface, so that only one wire (and ground)

needs to be connected from a central microprocessor to a DS18B20. Power for reading, writing, and

performing temperature conversions can be derived from the data line itself with no need for an external

power source.

Because each DS18B20 contains a unique silicon serial number, multiple DS18B20s can exist on the

same 1-Wire bus. This allows for placing temperature sensors in many different places. Applications

where this feature is useful include HVAC environmental controls, sensing temperatures inside buildings,

equipment or machinery, and process monitoring and control.

DS18B20

Programmable Resolution

1-Wire

Digital Thermomete

www.dalsemi.com

PRELIMINARY

DALLAS

DS1820

1 2 3

GND

VDD

1 2 3

BOTTOM VIEW

DS18B20 To-92

Package

GND

DS18B20Z

8-Pin SOIC (150 mil)

Summary of content (27 pages)

PAGE 1
PRELIMINARY DS18B20 Programmable Resolution 1-Wire® Digital Thermometer www.dalsemi.com Unique 1-Wire interface requires only one port pin for communication Multidrop capability simplifies distributed temperature sensing applications Requires no external components Can be powered from data line. Power supply range is 3.0V to 5.5V Zero standby power required Measures temperatures from -55°C to +125°C. Fahrenheit equivalent is -67°F to +257°F ±0.
PAGE 2
DS18B20 DETAILED PIN DESCRIPTION Table 1 PIN 8PIN SOIC 5 4 PIN TO92 1 2 SYMBOL GND DQ DESCRIPTION Ground. Data Input/Output pin. For 1-Wire operation: Open drain. (See “Parasite Power” section.) 3 3 VDD Optional VDD pin. See “Parasite Power” section for details of connection. VDD must be grounded for operation in parasite power mode. DS18B20Z (8-pin SOIC): All pins not specified in this table are not to be connected. OVERVIEW The block diagram of Figure 1 shows the major components of the DS18B20.
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DS18B20 DS18B20 BLOCK DIAGRAM Figure 1 MEMORY AND CONTROL LOGIC 64-BIT ROM AND 1-WIRE PORT DQ INTERNAL VDD TEMPERATURE SENSOR SCRATCHPAD HIGH TEMPERATURE TRIGGER, TH LOW TEMPERATURE TRIGGER, TL VDD POWER SUPPLY SENSE 8-BIT CRC GENERATOR CONFIGURATION REGISTER PARASITE POWER The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power whenever the DQ or VDD pins are high.
PAGE 4
DS18B20 For situations where the bus master does not know whether the DS18B20s on the bus are parasite powered or supplied with external VDD, a provision is made in the DS18B20 to signal the power supply scheme used. The bus master can determine if any DS18B20s are on the bus which require the strong pullup by sending a Skip ROM protocol, then issuing the read power supply command. After this command is issued, the master then issues read time slots.
PAGE 5
DS18B20 OPERATION - MEASURING TEMPERATURE The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the DS18B20 is configurable (9, 10, 11, or 12 bits), with 12-bit readings the factory default state. This equates to a temperature resolution of 0.5°C, 0.25°C, 0.125°C, or 0.0625°C.
PAGE 6
DS18B20 64-BIT LASERED ROM Each DS18B20 contains a unique ROM code that is 64-bits long. The first 8 bits are a 1-Wire family code (DS18B20 code is 28h). The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. (See Figure 4.) The 64-bit ROM and ROM Function Control section allow the DS18B20 to operate as a 1-Wire device and follow the 1-Wire protocol detailed in the section “1-Wire Bus System.
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DS18B20 ROM FUNCTIONS FLOW CHART Figure 5 7 of 27
PAGE 8
DS18B20 1-WIRE CRC CODE Figure 6 INPUT XOR XOR XOR (MSB) (LSB) MEMORY The DS18B20’s memory is organized as shown in Figure 8. The memory consists of a scratchpad RAM and a nonvolatile, electrically erasable (E2) RAM, which stores the high and low temperature triggers TH and TL, and the configuration register. The scratchpad helps insure data integrity when communicating over the 1-Wire bus. Data is first written to the scratchpad using the Write Scratchpad [4Eh] command.
PAGE 9
DS18B20 R0, R1: Thermometer resolution bits. Table 3 below defines the resolution of the digital thermometer, based on the settings of these 2 bits. There is a direct tradeoff between resolution and conversion time, as depicted in the AC Electrical Characteristics. The factory default of these EEPROM bits is R0=1 and R1=1 (12-bit conversions). Thermometer Resolution Configuration Table 3 R1 R0 0 0 1 1 0 1 0 1 Thermometer Resolution 9 bit 10 bit 11 bit 12 bit Max Conversion Time 93.
PAGE 10
DS18B20 1-WIRE BUS SYSTEM The 1-Wire bus is a system which has a single bus master and one or more slaves. The DS18B20 behaves as a slave. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). HARDWARE CONFIGURATION The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time.
PAGE 11
DS18B20 INITIALIZATION All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the DS18B20 is on the bus and is ready to operate. For more details, see the “1-Wire Signaling” section.
PAGE 12
DS18B20 Example of a ROM Search The ROM search process is the repetition of a simple three-step routine: read a bit, read the complement of the bit, then write the desired value of that bit. The bus master performs this simple, three-step routine on each bit of the ROM. After one complete pass, the bus master knows the contents of the ROM in one device. The remaining number of devices and their ROM codes may be identified by additional passes.
PAGE 13
DS18B20 8. The bus master writes a 0-bit. connected. This deselects ROM1, leaving ROM4 as the only device still 9. The bus master reads the remainder of the ROM bits for ROM4 and continues to access the part if desired. This completes the first pass and uniquely identifies one part on the 1-Wire bus. 10. The bus master starts a new ROM search sequence by repeating steps 1 through 7. 11. The bus master writes a 1-bit. This decouples ROM4, leaving only ROM1 still coupled. 12.
PAGE 14
DS18B20 The initialization sequence required to begin any communication with the DS18B20 is shown in Figure 11. A reset pulse followed by a presence pulse indicates the DS18B20 is ready to send or receive data given the correct ROM command and memory function command. The bus master transmits (TX) a reset pulse (a low signal for a minimum of 480 µs). The bus master then releases the line and goes into a receive mode (RX). The 1-Wire bus is pulled to a high state via the 5k pullup resistor.
PAGE 15
DS18B20 MEMORY FUNCTIONS FLOW CHART Figure 10 15 of 27
PAGE 16
DS18B20 MEMORY FUNCTIONS FLOW CHART Figure 10 (cont’d) 16 of 27
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DS18B20 MEMORY FUNCTIONS FLOW CHART Figure 10 (cont’d) 17 of 27
PAGE 18
DS18B20 INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 11 DS18B20 COMMAND SET Table 4 1-WIRE BUS AFTER ISSUING INSTRUCTION DESCRIPTION PROTOCOL PROTOCOL TEMPERATURE CONVERSION COMMANDS Convert T Initiates temperature 44h MEMORY COMMANDS Read Scratchpad Reads bytes from BEh scratchpad and reads CRC byte. Write Scratchpad Writes bytes into 4Eh
PAGE 19
DS18B20 NOTES: 1. Temperature conversion takes up to 750 ms. After receiving the Convert T protocol, if the part does not receive power from the VDD pin, the DQ line for the DS18B20 must be held high for at least a period greater than tconv to provide power during the conversion process. As such, no other activity may take place on the 1-Wire bus for at least this period after a Convert T command has been issued. 2.
PAGE 20
DS18B20 READ/WRITE TIMING DIAGRAM Figure 12 20 of 27
PAGE 21
DS18B20 DETAILED MASTER READ 1 TIMING Figure 13 RECOMMENDED MASTER READ 1 TIMING Figure 14 21 of 27
PAGE 22
DS18B20 Related Application Notes The following Application Notes can be applied to the DS18B20. These notes can be obtained from the Dallas Semiconductor “Application Note Book,” via our website at http://www.dalsemi.com/.
PAGE 23
DS18B20 MEMORY FUNCTION EXAMPLE Table 6 Example: Bus Master writes memory (parasite power and only one DS18B20 assumed). MASTER MODE TX RX TX TX TX TX RX TX TX RX DATA (LSB FIRST) Reset Presence CCh 4Eh <3 data bytes> Reset Presence CCh BEh <9 data bytes> TX RX TX TX Reset Presence CCh 48h TX RX Reset Presence COMMENTS Reset pulse. Presence pulse. Skip ROM command. Write Scratchpad command. Writes three bytes to scratchpad (TH, TL, and config). Reset pulse. Presence pulse. Skip ROM command.
PAGE 24
DS18B20 ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -0.5V to +6.0V -55°C to +125°C -55°C to +125°C See J-STD-020A specification * This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
PAGE 25
DS18B20 AC ELECTRICAL CHARACTERISTICS: PARAMETER Temperature Conversion Time Time Slot Recovery Time Write 0 Low Time Write 1 Low Time Read Data Valid Reset Time High Reset Time Low Presence Detect High Presence Detect Low Capacitance SYMBOL tCONV (-55°C to +125°C; VDD=3.0V to 5.5V) CONDITION MIN TYP MAX 9 bit 93.75 10 bit 11 bit 12 bit 187.
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DS18B20 26 of 27
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DS18B20 TYPICAL PERFORMANCE CURVE DS18B20 Typical Error Curve 0.5 0.4 0.3 +3σ Error 0.2 0.1 0 0 10 20 30 40 50 60 -0.1 -0.2 Mean Error -0.3 -0.4 -3σ Error -0.