Maxim Electronics DS18B20

Reference Designs (56)

Attributes

Part Number
Manufacturer
Datasheet
Prefix
U
Centroid Not Specified
No
Digikey Description
SENSOR TEMPERATURE 1-WIRE TO92-3
Digikey Part Number
DS18B20-ND
Ipc Land Pattern Name
TO-92
Lead Free
yes
Mouser Part Number
700-DS18B20
Package
TO-92
RoHS
yes
Temperature Range High
+125°C
Temperature Range Low
-55°C
Verified Attributes
true
Verified Geometry
true
Verified Pad Assignment
true
Verified Pin Names
true
Mechanical Drawing
http://pdfserv.maximintegrated.com/package_dwgs/21-0248.PDF

Pins

1
GND
2
DQ
3
VDD

Contributors

Datasheet Preview

AVAILABLE
Functional Diagrams
Pin Configurations appear at end of data sheet.
Functional Diagrams continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
For pricing, delivery, and
ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maxim
integrated.com.
REV: 042208
DESCRIPTION
The DS18B20 digital thermometer provides 9-bit
to 12-bit Celsius 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.
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
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
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
750ms (Max)
User-Definable Nonvolatile (NV) Alarm
Settings
Alarm Search Command Identifies and
Addresses Devices Whose Temperature is
Outside Programmed Limits (Temperature
Alarm Condition)
Available in 8-Pin SO (150 mils), 8-Pin µSOP,
and 3-Pin TO-92 Packages
Software Compatible with the DS1822
Applications Include Thermostatic Controls,
Industrial Systems, Consumer Products,
Thermometers, or Any Thermally Sensitive
System
PIN CONFIGURATIONS
DS18B20
Programmable Resolution
1-
Wire Digital Thermometer
TO-92
(DS18B20)
1
(BOTTOM VIEW)
2
3
MAXIM
18B20
GND
DQ
V
DD
3
SO (150 mils)
(DS18B20Z)
N.C.
N.C.
N.C.
N.C.
GND
DQ
V
DD
N.C.
6
8
7
5
3
1
2
4
MAXIM
18B20
N.C.
V
DD
N.C.
N.C.
N.C.
GND
N.C.
DQ
6
8
7
5
3
1
2
4
18B20
µSOP
(DS18B20U)
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
DS18B20
2 of 22
ORDERING INFORMATION
PART
TEMP RANGE
PIN-PACKAGE
TOP MARK
DS18B20
-55
°
C to +125
°
C
3 TO-92
18B20
DS18B20+
-55°C to +125°C
3 TO-92
18B20
DS18B20/T&R
-55°C to +125°C
3 TO-92 (2000 Piece)
18B20
DS18B20+T&R
-55°C to +125°C
3 TO-92 (2000 Piece)
18B20
DS18B20-SL/T&R
-55
°
C to +125
°
C
3 TO-92 (2000 Piece)*
18B20
DS18B20-SL+T&R
-55°C to +125°C
3 TO-92 (2000 Piece)*
18B20
DS18B20U
-55°C to +125°C
8 µSOP
18B20
DS18B20U+
-55°C to +125°C
8 µSOP
18B20
DS18B20U/T&R
-55
°
C to +125
°
C
8
µ
SOP (3000 Piece)
18B20
DS18B20U+T&R
-55
°
C to +125
°
C
8
µ
SOP (3000 Piece)
18B20
DS18B20Z
-55
°
C to +125
°
C
8 SO
DS18B20
DS18B20Z+
-55°C to +125°C
8 SO
DS18B20
DS18B20Z/T&R
-55
°
C to +125
°
C
8 SO (2500 Piece)
DS18B20
DS18B20Z+T&R
-55°C to +125°C
8 SO (2500 Piece)
DS18B20
+Denotes a 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 SLfor straight leads. Bulk TO-92 orders are straight
leads only.
PIN DESCRIPTION
PIN
NAME FUNCTION
SO
µ
SOP
TO-92
1, 2, 6,
7, 8
2, 3, 5,
6, 7
N.C. No Connection
3 8 3 V
DD
Optional V
DD
. V
DD
must be grounded for operation in
parasite power mode.
4 1 2 DQ
Data Input/Output. Open-drain 1-Wire interface pin. Also
provides power to the device when used in parasite power
mode (see the Powering the DS18B20 section.)
5 4 1 GND Ground
OVERVIEW
Figure 1 shows a block diagram of the DS18B20, and pin descriptions are given in the Pin Description
table. 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 (T
H
and T
L
) 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 T
H
, T
L
, 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 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
DS18B20
3 of 22
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.
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 (C
PP
), 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 V
DD
.
Figure 1. DS18B20 Block Diagram
OPERATIONMEASURING TEMPERATURE
The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the
temperature 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 DS18B20
powers up in a low-power idle state. To initiate a temperature measurement and A-to-D conversion, the
master must issue a Convert T [44h] command. Following the conversion, the resulting thermal data is
stored in the 2-byte temperature register in the scratchpad memory and the DS18B20 returns to its idle
state. If the DS18B20 is powered by an external supply, the master can issue “read time slots” (see the
1-Wire Bus System section) after the Convert T command and the DS18B20 will respond by transmitting
0 while the temperature conversion is in progress and 1 when the conversion is done. If the DS18B20 is
powered with parasite power, this notification technique cannot be used since the bus must be pulled high
by a strong pullup during the entire temperature conversion. The bus requirements for parasite power are
explained in detail in the Powering the DS18B20 section.
The DS18B20 output temperature data is calibrated in degrees Celsius; for Fahrenheit applications, a
lookup table or conversion routine must be used. The temperature data is stored as a 16-bit sign-extended
two’s complement number in the temperature register (see Figure 2). The sign bits (S) indicate if the
temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the
DS18B20 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-bit
resolution bits 2, 1, and 0 are undefined. Table 1 gives examples of digital output data and the
corresponding temperature reading for 12-bit resolution conversions.
V
PU
4.7k
POWER-
SUPPLY
SENSE
64-BIT ROM
AND
1-Wire PORT
DQ
V
DD
INTERNAL V
DD
C
PP
PARASITE POWER
CIRCUIT
MEMORY CONTROL
LOGIC
SCRATCHPAD
8-BIT CRC GENERATOR
TEMPERATURE SENSOR
ALARM HIGH TRIGGER (T
H
)
REGISTER (EEPROM)
ALARM LOW TRIGGER (T
L
)
REGISTER (EEPROM)
CONFIGURATION REGISTER
(EEPROM)
GND
DS18B20
DS18B20
4 of 22
Figure 2. Temperature Register Format
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
LS BYTE
2
3
2
2
2
1
2
0
2
-1
2
-2
2
-3
2
-4
BIT 15
BIT 14
BIT 13
BIT 12
BIT 11
BIT 10
BIT 9
BIT 8
MS BYTE
S S S S S 2
6
2
5
2
4
S = SIGN
Table 1. Temperature/Data Relationship
TEMPERATURE (
°
C)
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
+125 0000 0111 1101 0000 07D0h
+85* 0000 0101 0101 0000 0550h
+25.0625 0000 0001 1001 0001 0191h
+10.125 0000 0000 1010 0010 00A2h
+0.5 0000 0000 0000 1000 0008h
0 0000 0000 0000 0000 0000h
-0.5 1111 1111 1111 1000 FFF8h
-10.125 1111 1111 0101 1110 FF5Eh
-25.0625 1111 1110 0110 1111 FE6Fh
-55 1111 1100 1001 0000 FC90h
*The power-on reset value of the temperature register is +85°C.
OPERATIONALARM SIGNALING
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 T
H
and T
L
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
H
and T
L
registers are nonvolatile (EEPROM) so they will retain data when the
device is powered down. T
H
and T
L
can be accessed through bytes 2 and 3 of the scratchpad as explained
in the Memory section.
Figure 3. T
H
and T
L
Register Format
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
S 2
6
2
5
2
4
2
3
2
2
2
1
2
0
Only bits 11 through 4 of the temperature register are used in the T
H
and T
L
comparison since T
H
and T
L
are 8-bit registers. If the measured temperature is lower than or equal to T
L
or higher than or equal to T
H
,
an alarm condition exists and an alarm flag is set inside the DS18B20. 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.