Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsDS18B20+PAR

1 of 19 101207

FEATURES

• Unique 1-Wire

interface requires only one

port pin for communication

• Derives power from data line (“parasite

power”)—does not need a local power supply

• Multi-drop capability simplifies distributed

temperature sensing applications

• Requires no external components

• ±0.5°C accuracy from –10°C to +85°C

• Measures temperatures from –55°C to

+100°C (–67°F to +212°F)

• Thermometer resolution is user-selectable

from 9 to 12 bits

• Converts temperature to 12-bit digital word in

750 ms (max.)

• User–definable non-volatile temperature

alarm settings

• Alarm search command identifies and

addresses devices whose temperature is

outside of programmed limits (temperature

alarm condition)

• Software compatible with the DS1822-PAR

• Ideal for use in remote sensing applications

(e.g., temperature probes) that do not have a

local power source

PIN ASSIGNMENT

PIN DESCRIPTION

GND - Ground

DQ - Data In/Out

NC - No Connect

DESCRIPTION

The DS18B20-PAR digital thermometer provides 9 to 12–bit centigrade temperature measurements and

has an alarm function with nonvolatile user-programmable upper and lower trigger points. The

DS18B20-PAR does not need an external power supply because it derives power directly from the data

line (“parasite power”). The DS18B20-PAR communicates over a 1-Wire bus, which by definition

requires only one data line (and ground) for communication with a central microprocessor. It has an

operating temperature range of –55°C to +100°C and is accurate to ±0.5°C over a range of –10°C to

+85°C.

Each DS18B20-PAR has a unique 64-bit identification code, which allows multiple DS18B20-PARs to

function on the same 1–wire bus; thus, it is simple to use one microprocessor to control many DS18B20-

PARs distributed over a large area. Applications that can benefit from this feature include HVAC

environmental controls, temperature monitoring systems inside buildings, equipment or machinery, and

process monitoring and control systems.

DS18B20-PAR

1-Wire Parasite-Powe

Digital Thermomete

www.maxim

ic.com

TO-92

(

DS18B20-PAR

)

(

BOTTOM VIEW

)

2 3

DALLAS

18B20P

GND

2 3

1-Wire is a registered trademark of Dallas Semiconductor.

Summary of content (19 pages)

PAGE 1
DS18B20-PAR 1-Wire Parasite-Power Digital Thermometer www.maxim-ic.com FEATURES • • • • • • • • • • • Unique 1-Wire interface requires only one port pin for communication Derives power from data line (“parasite power”)—does not need a local power supply Multi-drop capability simplifies distributed temperature sensing applications Requires no external components ±0.
PAGE 2
DS18B20-PAR DETAILED PIN DESCRIPTIONS Table 1 PIN 1 2 SYMBOL GND DQ 3 NC DESCRIPTION Ground. Data Input/Output pin. Open-drain 1-Wire interface pin. Also provides power to the device when used in parasite power mode (see “Parasite Power” section.) No Connect. Doesn’t connect to internal circuit. OVERVIEW The DS18B20-PAR uses Dallas’ exclusive 1-Wire bus protocol that implements bus communication using one control signal.
PAGE 3
DS18B20-PAR PARASITE POWER The DS18B20-PAR’s parasite power circuit allows the DS18B20-PAR to operate without a local external power supply. This ability is especially useful for applications that require remote temperature sensing or that are very space constrained. Figure 1 shows the DS18B20-PAR’s parasite-power control circuitry, which “steals” power from the 1-Wire bus via the DQ pin when the bus is high.
PAGE 4
DS18B20-PAR resolution, bits 1 and 0 are undefined, and for 9-bit resolution bits 2, 1 and 0 are undefined. Table 2 gives examples of digital output data and the corresponding temperature reading for 12-bit resolution conversions.
PAGE 5
DS18B20-PAR The master device can check the alarm flag status of all DS DS18B20-PARs on the bus by issuing an Alarm Search [ECh] command. Any DS18B20-PARs with a set alarm flag will respond to the command, so the master can determine exactly which DS18B20-PARs have experienced an alarm condition. If an alarm condition exists and the TH or TL settings have changed, another temperature conversion should be done to validate the alarm condition.
PAGE 6
DS18B20-PAR DS18B20-PAR MEMORY MAP Figure 6 SCRATCHPAD (Power-up State) byte 0 Temperature LSB (50h) (85°C) byte 1 Temperature MSB (05h) EEPROM byte 2 TH Register or User Byte 1* TH Register or User Byte 1 byte 3 TL Register or User Byte 2* TL Register or User Byte 2 byte 4 Configuration Register* Configuration Register byte 5 Reserved (FFh) byte 6 Reserved byte 7 Reserved (10h) byte 8 CRC* *Power-up state depends on value(s) stored in EEPROM CONFIGURATION REGISTER Byte 4 of the scratchpad memor
PAGE 7
DS18B20-PAR and then compare this value to either the ROM code CRC (for ROM reads) or to the scratchpad CRC (for scratchpad reads). If the calculated CRC matches the read CRC, the data has been received error free. The comparison of CRC values and the decision to continue with an operation are determined entirely by the bus master.
PAGE 8
DS18B20-PAR HARDWARE CONFIGURATION Figure 9 VPU Microprocessor Strong Pullup VPU DS18B20-PAR 1-WIRE PORT 4.7K RX 1-wire bus DQ Pin RX 5 μA Typ. TX 100 Ω MOSFET TX RX = RECEIVE TX = TRANSMIT TRANSACTION SEQUENCE The transaction sequence for accessing the DS18B20-PAR is as follows: Step 1. Initialization Step 2. ROM Command (followed by any required data exchange) Step 3.
PAGE 9
DS18B20-PAR cycle (i.e., Search ROM command followed by data exchange) as many times as necessary to identify all of the slave devices. If there is only one slave on the bus, the simpler Read ROM command (see below) can be used in place of the Search ROM process. For a detailed explanation of the Search ROM procedure, refer to the iButton® Book of Standards at www.ibutton.com/ibuttons/standard.pdf.
PAGE 10
DS18B20-PAR transmitted least significant bit first. All three bytes MUST be written before the master issues a reset, or the data may be corrupted. READ SCRATCHPAD [BEh] This command allows the master to read the contents of the scratchpad. The data transfer starts with the least significant bit of byte 0 and continues through the scratchpad until the 9th byte (byte 8 – CRC) is read. If only part of the scratchpad contents is required, the master may issue a reset to terminate reading at any time.
PAGE 11
DS18B20-PAR ROM COMMANDS FLOW CHART Figure 10 Initialization Sequence MASTER TX RESET PULSE DS18B20-PAR TX PRESENCE PULSE MASTER TX ROM COMMAND 33h READ ROM COMMAND Y N 55h MATCH ROM COMMAND F0h SEARCH ROM COMMAND N Y N Y ECh ALARM SEARCH COMMAND CCh SKIP ROM COMMAND N Y Y MASTER TX BIT 0 DS18B20-PAR TX BIT 0 DS18B20-PAR TX BIT 0 DS18B20-PAR TX BIT 0 DS18B20-PAR TX BIT 0 MASTER TX BIT 0 MASTER TX BIT 0 DS18B20-PAR TX FAMILY CODE 1 BYTE N BIT 0 MATCH? DS18B20-PAR TX SERIAL NUMBER 6
PAGE 12
DS18B20-PAR DS18B20-PAR FUNCTION COMMANDS FLOW CHART Figure 11 44h CONVERT TEMPERATURE ? MASTER TX FUNCTION COMMAND 48h COPY SCRATCHPAD ? N Y Y MASTER ENABLES STRONG PULL-UP ON DQ MASTER ENABLES STRONG PULLUP ON DQ DATA COPIED FROM SCRATCHPAD TO EEPROM DS18B20-PAR CONVERTS TEMPERATURE MASTER DISABLES STRONG PULLUP MASTER DISABLES STRONG PULLUP N B8h RECALL E2 ? BEh READ SCRATCHPAD ? N Y N Y 4Eh WRITE SCRATCHPAD ? Y MASTER TX TH BYTE TO SCRATCHPAD MASTER RX DATA BYTE FROM SCRATCHPAD MAS
PAGE 13
DS18B20-PAR 1-WIRE SIGNALING The DS18B20-PAR uses a strict 1-Wire communication protocol to insure data integrity. Several signal types are defined by this protocol: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. All of these signals, with the exception of the presence pulse, are initiated by the bus master.
PAGE 14
DS18B20-PAR The DS18B20-PAR samples the 1-Wire bus during a window that lasts from 15 μs to 60 μs after the master initiates the write time slot. If the bus is high during the sampling window, a 1 is written to the DS18B20-PAR. If the line is low, a 0 is written to the DS18B20-PAR.
PAGE 15
DS18B20-PAR the read time slot. Therefore, the master must release the bus and then sample the bus state within 15 μs from the start of the slot. Figure 14 illustrates that the sum of TINIT, TRC, and TSAMPLE must be less than 15 μs for a read time slot. Figure 15 shows that system timing margin is maximized by keeping TINIT and TRC as short as possible and by locating the master sample time during read time slots towards the end of the 15 μs period.
PAGE 16
DS18B20-PAR MASTER MODE RX DATA (LSB FIRST) 9 data bytes COMMENTS Master reads entire scratchpad including CRC. The master then recalculates the CRC of the first eight data bytes from the scratchpad and compares the calculated CRC with the read CRC (byte 9). If they match, the master continues; if not, the read operation is repeated. DS18B20-PAR OPERATION EXAMPLE 2 In this example there is only one DS18B20-PAR on the bus.
PAGE 17
DS18B20-PAR ABSOLUTE MAXIMUM RATINGS* Voltage on any pin relative to ground Operating temperature Storage temperature Soldering temperature –0.5V to +6.0V –55°C to +100°C –55°C to +125°C See J-STD-020A Specification *These are stress ratings 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 18
DS18B20-PAR AC ELECTRICAL CHARACTERISTICS PARAMETER SYMBOL Temperature Conversion tCONV Time Time to Strong Pullup On tSPON 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 tSLOT tREC rLOW0 tLOW1 tRDV tRSTH tRSTL (-55°C to +100°C; VPU=3.0V to 5.
PAGE 19
DS18B20-PAR TIMING DIAGRAMS Figure 17 19 of 19