DS18B20. 18B20 Datasheet

18B20 DS18B20. Datasheet pdf. Equivalent

Part 18B20
Description DS18B20
Feature DS18B20 Programmable Resolution 1-Wire® Digital Thermometer www.dalsemi.com www.datasheet4u.com FEA.
Manufacture Dallas Semiconductor
Datasheet
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18B20
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Unique 1-wire interface requires only one
port pin for communication
Each device has a unique 64-bit serial code
stored in an on-board ROM
Multi-drop 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
Measures temperatures from –55°C to
+125°C (–67°F to +257°F)
• ±0.5°C accuracy from –10°C to +85°C
Thermometer resolution is user-selectable
from 9 to 12 bits
Converts temperature to 12-bit digital word in
750 ms (max.)
User-definable nonvolatile alarm settings
Alarm search command identifies and
addresses devices whose temperature is
outside of programmed limits (temperature
alarm condition)
Software compatible with the DS1822
Applications include thermostatic controls,
industrial systems, consumer products,
thermometers, or any thermally sensitive
system
DS18B20
Programmable Resolution
1-Wire® Digital Thermometer
PIN ASSIGNMENT
DALLAS
18B20
123
NC 1
8 NC
NC 2
7 NC
VDD
3
6 NC
DQ 4
5 GND
8-pin 150-mil SOIC
(DS18B20Z)
12 3
(BOTTOM VIEW)
TO-92
(DS18B20)
PIN DESCRIPTION
GND - Ground
DQ - Data In/Out
VDD - Power Supply Voltage
NC - No Connect
DESCRIPTION
The DS18B20 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
communicates over a 1-wire bus that 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 +125°C
and is accurate to ±0.5°C over the range of –10°C to +85°C. In addition, the DS18B20 can derive power
directly from the data line (“parasite power”), eliminating the need for an external power supply.
Each DS18B20 has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same
1–wire bus; thus, it is simple to use one microprocessor to control many DS18B20s 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.
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18B20
DS18B20
DETAILED PIN DESCRIPTIONS Table 1
8-PIN SOIC* TO-92 SYMBOL DESCRIPTION
5 1 GND Ground.
4
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2
DQ 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.)
3 3 VDD Optional VDD pin. VDD must be grounded for operation in
parasite power mode.
*All pins not specified in this table are “No Connect” pins.
OVERVIEW
Figure 1 shows a block diagram of the DS18B20, and pin descriptions are given in Table 1. The 64-bit
ROM stores the device’s unique serial code. The scratchpad memory contains the 2-byte temperature
register that stores the digital output from the temperature sensor. In addition, the scratchpad provides
access to the 1-byte upper and lower alarm trigger registers (TH and TL), and the 1-byte configuration
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 Dallas’ exclusive 1-wire bus protocol that implements bus communication using one
control signal. The control line requires a weak pullup resistor since all devices are linked to the bus via a
3-state or open-drain port (the DQ pin in the case of the DS18B20). In this bus system, the
microprocessor (the master device) identifies and addresses devices on the bus using each device’s unique
64-bit code. Because each device has a unique code, the number of devices that can be addressed on one
bus is virtually unlimited. The 1-wire bus protocol, including detailed explanations of the commands and
“time slots,” is covered in the 1-WIRE BUS SYSTEM section of this datasheet.
Another feature of the DS18B20 is the ability to operate without an external power supply. Power is
instead supplied through the 1-wire pullup resistor via the DQ pin when the bus is high. The high bus
signal also charges an internal capacitor (CPP), which then supplies power to the device when the bus is
low. This method of deriving power from the 1-wire bus is referred to as “parasite power.” As an
alternative, the DS18B20 may also be powered by an external supply on VDD.
DS18B20 BLOCK DIAGRAM Figure 1
VPU
4.7K
DQ
GND
VDD
PARASITE POWER
CIRCUIT
INTERNAL VDD
CPP
POWER
SUPPLY
SENSE
64-BIT ROM
AND
1-wire PORT
MEMORY CONTROL
LOGIC
DS18B20
SCRATCHPAD
TEMPERATURE SENSOR
ALARM HIGH TRIGGER (TH)
REGISTER (EEPROM)
ALARM LOW TRIGGER (TL)
REGISTER (EEPROM)
CONFIGURATION REGISTER
(EEPROM)
8-BIT CRC GENERATOR
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