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043001
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 55C to
+125C (67F to +257F)
2.0
C accuracy from 0C to +70C
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
PIN DESCRIPTION
GND -
Ground
DQ -
Data
In/Out
V
DD
- Power Supply Voltage
DESCRIPTION
The DS18B20X Digital Thermometer provides 9 to 12bit 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 55C to +125C
and is accurate to
2.0
C over the range of 0C to +70C. 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 1wire 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.
DS18B20X
Flipchip 1-Wire
Digital Thermometer
www.dalsemi.com
GND
GND
DQ
VDD
Branding legend:
28 = family code
rr = revision code (i.e., B6)
d = one letter date code
(TOP VIEW)
28rrd
See Mechanical Specification
(page 21) for package dimensions.
DS18B20X
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DETAILED PIN DESCRIPTIONS Table 1
SYMBOL DESCRIPTION
GND
Ground.
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.)
V
DD
Optional V
DD
pin. V
DD
must be grounded for operation in
parasite power mode.
OVERVIEW
Figure 1 shows a block diagram of the DS18B20X, 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 (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 DS18B20X 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 DS18B20X). 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 DS18B20X 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 DS18B20X may also be powered by an external supply on V
DD
.
DS18B20X BLOCK DIAGRAM Figure 1
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
DS18B20X
DS18B20X
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OPERATION MEASURING TEMPERATURE
The core functionality of the DS18B20X 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
DS18B20X 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 DS18B20X
returns to its idle state. If the DS18B20X 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 DS18B20X
will respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion
is done. If the DS18B20X 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 DS18B20X section of
this datasheet.
The DS18B20X output temperature data is calibrated in degrees centigrade; 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
DS18B20X 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 2 gives examples of digital output data and the
corresponding temperature reading for 12-bit resolution conversions.
TEMPERATURE REGISTER FORMAT Figure 2
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
TEMPERATURE/DATA RELATIONSHIP Table 2
TEMPERATURE DIGITAL
OUTPUT
(Binary)
DIGITAL OUTPUT
(Hex)
+125C
0000 0111 1101 0000
07D0h
+85C*
0000 0101 0101 0000
0550h
+25.0625C
0000 0001 1001 0001
0191h
+10.125C
0000 0000 1010 0010
00A2h
+0.5C
0000 0000 0000 1000
0008h
0C
0000 0000 0000 0000
0000h
-0.5C
1111 1111 1111 1000
FFF8h
-10.125C
1111 1111 0101 1110
FF5Eh
-25.0625C
1111 1110 0110 1111
FE6Fh
-55C
1111 1100 1001 0000
FC90h
*The power-on reset value of the temperature register is +85C
DS18B20X
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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
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 of this datasheet.
T
H
AND T
L
REGISTER FORMAT Figure 3
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
S 2
6
2
5
2
5
2
5
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 result of a temperature measurement is higher than T
H
or lower than T
L
, 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
H
or T
L
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
DD
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
PP
) to provide power when the bus is
low. When the DS18B20X is used in parasite power mode, the V
DD
pin must be connected to ground.
In parasite power mode, the 1-wire bus and C
PP
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
PP
. 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
s (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
wr
= 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
DD
pin, as shown in Figure 5. The advantage of this method is that the MOSFET pullup is not
required, and the 1wire bus is free to carry other traffic during the temperature conversion time.
DS18B20X
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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
POWERING THE DS18B20X WITH AN EXTERNAL SUPPLY Figure 5
64-BIT LASERED ROM CODE
Each DS18B20X contains a unique 64bit code (see Figure 6) stored in ROM. The least significant 8 bits
of the ROM code contain the DS18B20X's 1wire 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 64bit ROM code and associated ROM function control logic
allow the DS18B20X to operate as a 1wire 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
48-BIT SERIAL NUMBER
8-BIT FAMILY CODE (28h)
MSB MSB
LSB LSB
LSB
MSB
V
DD
(External Supply)
DS18B20X
GND
V
DD
DQ
V
PU
4.7K
To Other
1-Wire Devices
1-Wire Bus
Micro-
processor
V
PU
V
PU
4.7K
1-Wire Bus
Micro-
processor
DS18B20X
GND
V
DD
DQ
To Other
1-Wire Devices
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