1-Wire is a registered trademark of Maxim Integrated Products, Inc.
BOTTOM VIEW
1
µSOP
(DS18B20U)
TO-92
(DS18B20)
19-7487; Rev 4; 1/15
DS18B20
Programmable Resolution
1-Wire Digital Thermometer
Absolute Maximum Ratings
Voltage Range on Any Pin Relative to Ground ....-0.5V to +6.0V
Operating Temperature Range ......................... -55°C to +125°C
Storage Temperature Range ............................ -55°C to +125°C
Solder Temperature ...............................Refer to the IPC/JEDEC
J-STD-020 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.
DC Electrical Characteristics
(-55°C to +125°C; V
DD
= 3.0V to 5.5V)
PARAMETER
Supply Voltage
Pullup Supply Voltage
Thermometer Error
Input Logic-Low
Input Logic-High
Sink Current
Standby Current
Active Current
DQ Input Current
Drift
Note 1:
Note 2:
SYMBOL
V
DD
V
PU
t
ERR
V
IL
V
IH
I
L
I
DDS
I
DD
I
DQ
CONDITIONS
Local power (Note 1)
Parasite power
Local power
-10°C to +85°C
-55°C to +125°C
(Notes 1, 4, 5)
Local power
Parasite power
V
I/O
= 0.4V
(Notes 7, 8)
V
DD
= 5V (Note 9)
(Note 10)
(Note 11)
(Notes 1,6)
(Notes 1, 2)
(Note 3)
-0.3
+2.2
+3.0
4.0
750
1
5
±0.2
1000
1.5
MIN
+3.0
+3.0
+3.0
TYP
MAX
+5.5
+5.5
V
DD
±0.5
±2
+0.8
The lower
of 5.5 or
V
DD
+ 0.3
UNITS
V
V
°C
V
V
mA
nA
mA
µA
°C
All voltages are referenced to ground.
The Pullup Supply Voltage specification assumes that the pullup device is ideal, and therefore the high level of the
pullup is equal to V
PU
. In order to meet the V
IH
spec of the DS18B20, the actual supply rail for the strong pullup transis-
tor must include margin for the voltage drop across the transistor when it is turned on; thus: V
PU_ACTUAL
= V
PU_IDEAL
+
V
TRANSISTOR
.
Note 3:
See typical performance curve in
Figure 1.
Note 4:
Logic-low voltages are specified at a sink current of 4mA.
Note 5:
To guarantee a presence pulse under low voltage parasite power conditions, V
ILMAX
may have to be reduced to as low as
0.5V.
Note 6:
Logic-high voltages are specified at a source current of 1mA.
Note 7:
Standby current specified up to +70°C. Standby current typically is 3µA at +125°C.
Note 8:
To minimize I
DDS
, DQ should be within the following ranges: GND ≤ DQ ≤ GND + 0.3V or V
DD
– 0.3V ≤ DQ ≤ V
DD
.
Note 9:
Active current refers to supply current during active temperature conversions or EEPROM writes.
Note 10:
DQ line is high (“high-Z” state).
Note 11:
Drift data is based on a 1000-hour stress test at +125°C with V
DD
= 5.5V.
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2
DS18B20
Programmable Resolution
1-Wire Digital Thermometer
AC Electrical Characteristics–NV Memory
(-55°C to +125°C; V
DD
= 3.0V to 5.5V)
PARAMETER
NV Write Cycle Time
EEPROM Writes
EEPROM Data Retention
SYMBOL
t
WR
N
EEWR
t
EEDR
-55°C to +55°C
-55°C to +55°C
50k
10
CONDITIONS
MIN
TYP
2
MAX
10
UNITS
ms
writes
years
AC Electrical Characteristics
(-55°C to +125°C; V
DD
= 3.0V to 5.5V)
PARAMETER
SYMBOL
CONDITIONS
9-bit resolution
Temperature Conversion Time
t
CONV
10-bit resolution
11-bit resolution
12-bit resolution
Time to Strong Pullup On
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
t
SPON
t
SLOT
t
REC
t
LOW0
t
LOW1
t
RDV
t
RSTH
t
RSTL
t
PDHIGH
t
PDLOW
C
IN/OUT
Start convert T command issued
(Note 12)
(Note 12)
(Note 12)
(Note 12)
(Note 12)
(Note 12)
(Notes 12, 13)
(Note 12)
(Note 12)
480
480
15
60
60
240
25
60
1
60
1
120
15
15
(Note 12)
MIN
TYP
MAX
93.75
187.5
375
750
10
120
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
pF
ms
UNITS
Note 12:
See the timing diagrams in
Figure 2.
Note 13:
Under parasite power, if t
RSTL
> 960µs, a power-on reset can occur.
DS18B20 TYPICAL ERROR CURVE
0.5
0.4
THERMOMETER ERROR (°C)
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
0
MEAN ERROR
+3s ERROR
-3s ERROR
10
20
30
40
50
60
70
TEMPERATURE (°C)
Figure 1. Typical Performance Curve
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Maxim Integrated
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3
DS18B20
Programmable Resolution
1-Wire Digital Thermometer
1-WIRE WRITE ZERO TIME SLOT
t
SLOT
t
REC
t
LOW0
START OF NEXT CYCLE
1-WIRE READ ZERO TIME SLOT
t
SLOT
t
REC
START OF NEXT CYCLE
t
RDV
1-WIRE RESET PULSE
RESET PULSE FROM HOST
t
RSTL
t
RSTH
1-WIRE PRESENCE DETECT
PRESENCE DETECT
t
PDIH
t
PDLOW
Figure 2. Timing Diagrams
Pin Description
PIN
SO
1, 2, 6,
7, 8
3
4
5
µSOP
2, 3, 5,
6, 7
8
1
4
TO-92
—
3
2
1
NAME
N.C.
V
DD
DQ
GND
No Connection
Optional V
DD
. V
DD
must be grounded for operation in parasite power mode.
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.)
Ground
FUNCTION
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Maxim Integrated
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4
DS18B20
Programmable Resolution
1-Wire Digital Thermometer
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 “para-
site power.” As an alternative, the DS18B20 may also be
powered by an external supply on V
DD
.
Overview
Figure 3
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 configura-
tion 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 proto-
col 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.
Another feature of the DS18B20 is the ability to oper-
ate without an external power supply. Power is instead
supplied through the 1-Wire pullup resistor through the
Operation—Measuring Temperature
The core functionality of the DS18B20 is its direct-to-
digital temperature sensor. The resolution of the tempera-
ture 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 sup-
ply, 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 tem-
perature conversion is in progress and 1 when the con-
version 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
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