DS18B20X datasheet, PDF - EEWORLD Datasheet

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DS18B20X: DescriptionDIGITAL TEMP SENSOR-SERIAL, 12BIT(s), 2Cel, RECTANGULAR, SURFACE MOUNT; CategoryThe sensor Sensor/transducer; File Size170KB，21 Pages; ManufacturerDALLAS; Websitehttp://www.dalsemi.com

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DS18B20X Overview

DIGITAL TEMP SENSOR-SERIAL, 12BIT(s), 2Cel, RECTANGULAR, SURFACE MOUNT

DS18B20X Parametric

Parameter Name	Attribute value
Is it Rohs certified?	incompatible
Maker	DALLAS
package instruction	FCP-4
Reach Compliance Code	unknow
Maximum accuracy (Celsius)	2 Cel
body width	33.52 mm
body height	17.52 mm
Body length or diameter	49.02 mm
JESD-609 code	e0
Installation features	SURFACE MOUNT
Number of digits	12
Maximum working current	1 mA
Maximum operating temperature	125 °C
Minimum operating temperature	-55 °C
Output interface type	1-WIRE INTERFACE
Package body material	PLASTIC/EPOXY
Encapsulate equivalent code	FLIP CHIP
Package Shape/Form	RECTANGULAR
power supply	3.3/5 V
Sensor/Transducer Type	TEMPERATURE SENSOR,SWITCH/DIGITAL OUTPUT,SERIAL
Maximum supply voltage	5.5 V
Minimum supply voltage	3 V
surface mount	YES
Terminal surface	Tin/Lead (Sn/Pb)
Termination type	SOLDER

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DS18B20X

Flipchip 1-Wire

Digital Thermometer

www.dalsemi.com

FEATURES

•

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)

±2.0°C

accuracy from 0°C to +70°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)

Applications include thermostatic controls,

industrial systems, consumer products,

thermometers, or any thermally sensitive

system

PIN ASSIGNMENT

(TOP VIEW)

GND

VDD

28rrd

GND

Branding legend:

28 = family code

rr = revision code (i.e., B6)

d = one letter date code

See Mechanical Specification

(page 21) for package dimensions.

PIN DESCRIPTION

GND - Ground

- Data In/Out

- Power Supply Voltage

•

DESCRIPTION

The DS18B20X 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 DS18B20X

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

±2.0°C

over the range of 0°C to +70°C. In addition, the DS18B20X can derive power

directly from the data line (“parasite power”), eliminating the need for an external power supply.

Each DS18B20X has a unique 64-bit serial code, which allows multiple DS18B20Xs to function on the

same 1–wire bus; thus, it is simple to use one microprocessor to control many DS18B20Xs 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.

1 of 21

043001

DS18B20X

OPERATION – ALARM SIGNALING

After the DS18B20X performs a temperature conversion, the temperature value is compared to the user-

defined two’s complement alarm trigger values stored in the 1-byte T

and T

registers (see Figure 3).

The sign bit (S) indicates if the value is positive or negative: for positive numbers S = 0 and for negative

numbers S = 1. The T

and T

registers are nonvolatile (EEPROM) so they will retain data when the

device is powered down. T

and T

can be accessed through bytes 2 and 3 of the scratchpad as explained

in the MEMORY section of this datasheet.

AND T

Figure 3

bit 7

bit 6

bit 5

bit 4

bit 3

bit 2

bit 1

bit 0

Only bits 11 through 4 of the temperature register are used in the T

and T

comparison since T

and T

are 8-bit registers. If the result of a temperature measurement is higher than T

or lower than T

, an

alarm condition exists and an alarm flag is set inside the DS18B20X. This flag is updated after every

temperature measurement; therefore, if the alarm condition goes away, the flag will be turned off after the

next temperature conversion.

The master device can check the alarm flag status of all DS18B20Xs on the bus by issuing an Alarm

Search [ECh] command. Any DS18B20Xs with a set alarm flag will respond to the command, so the

master can determine exactly which DS18B20Xs have experienced an alarm condition. If an alarm

condition exists and the T

or T

settings have changed, another temperature conversion should be done

to validate the alarm condition.

POWERING THE DS18B20X

The DS18B20X can be powered by an external supply on the V

pin, or it can operate in “parasite

power” mode, which allows the DS18B20X to function without a local external supply. Parasite power

is very useful for applications that require remote temperature sensing or that are very space constrained.

Figure 1 shows the DS18B20X’s parasite-power control circuitry, which “steals” power from the 1-wire

bus via the DQ pin when the bus is high. The stolen charge powers the DS18B20X while the bus is high,

and some of the charge is stored on the parasite power capacitor (C

) to provide power when the bus is

low. When the DS18B20X is used in parasite power mode, the V

pin must be connected to ground.

In parasite power mode, the 1-wire bus and C

can provide sufficient current to the DS18B20X for most

operations as long as the specified timing and voltage requirements are met (refer to the DC

ELECTRICAL CHARACTERISTICS and the AC ELECTRICAL CHARACTERISTICS sections of this

data sheet). However, when the DS18B20X is performing temperature conversions or copying data from

the scratchpad memory to EEPROM, the operating current can be as high as 1.5 mA. This current can

cause an unacceptable voltage drop across the weak 1-wire pullup resistor and is more current than can be

supplied by C

. To assure that the DS18B20X has sufficient supply current, it is necessary to provide a

strong pullup on the 1-wire bus whenever temperature conversions are taking place or data is being

copied from the scratchpad to EEPROM. This can be accomplished by using a MOSFET to pull the bus

directly to the rail as shown in Figure 4. The 1-wire bus must be switched to the strong pullup within 10

µs

(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 (t

conv

) or data transfer (t

= 10 ms). No other

activity can take place on the 1-wire bus while the pullup is enabled.

The DS18B20X can also be powered by the conventional method of connecting an external power supply

to the V

pin, as shown in Figure 5. The advantage of this method is that the MOSFET pullup is not

required, and the 1–wire bus is free to carry other traffic during the temperature conversion time.

4 of 21

DS18B20X

The use of parasite power is not recommended for temperatures above 100°C since the DS18B20X may

not be able to sustain communications due to the higher leakage currents that can exist at these

temperatures. For applications in which such temperatures are likely, it is strongly recommended that the

DS18B20X be powered by an external power supply.

In some situations the bus master may not know whether the DS18B20Xs on the bus are parasite powered

or powered by external supplies. The master needs this information to determine if the strong bus pullup

should 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 DS18B20Xs will pull the bus low, and externally

powered DS18B20Xs will let the bus remain high. If the bus is pulled low, the master knows that it must

supply the strong pullup on the 1-wire bus during temperature conversions.

SUPPLYING THE PARASITE-POWERED DS18B20X DURING TEMPERATURE

CONVERSIONS

Figure 4

DS18B20X

Micro-

processor

4.7K

1-Wire Bus

To Other

1-Wire Devices

GND DQ V

POWERING THE DS18B20X WITH AN EXTERNAL SUPPLY

Figure 5

Micro-

processor

4.7K

1-Wire Bus

DS18B20X

GND DQ V

(External Supply)

To Other

1-Wire Devices

64-BIT LASERED ROM CODE

Each DS18B20X contains a unique 64–bit code (see Figure 6) stored in ROM. The least significant 8 bits

of the ROM code contain the DS18B20X’s 1–wire family code: 28h. The next 48 bits contain a unique

serial number. The most significant 8 bits contain a cyclic redundancy check (CRC) byte that is

calculated from the first 56 bits of the ROM code. A detailed explanation of the CRC bits is provided in

the CRC GENERATION section. The 64–bit ROM code and associated ROM function control logic

allow the DS18B20X to operate as a 1–wire device using the protocol detailed in the 1-WIRE BUS

SYSTEM section of this datasheet.

64-BIT LASERED ROM CODE

Figure 6

8-BIT CRC

MSB

LSB

48-BIT SERIAL NUMBER

MSB

5 of 21

LSB

8-BIT FAMILY CODE (28h)

MSB

LSB

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