MAXIM DS18S20 Technical data
1-Wire is a registered trademark of Maxim Integrated Products, Inc.
TO-92
1
(BOTTOM VIEW)
2
3
MAXIM
1
GND
DQ
V
2
3
SO (150 mils)
N.C.
N.C.
N.C.
N.C.
GND
DQ
VDD
N.C.
6 8 7 5 3
2
4
19-5474; Rev 8/10
DS18S20
Wire Digital Thermometer
High-Precision 1-
FEATURES
Unique 1-Wire® Interface Requ ires Only O ne
Port Pin for Co mmunic a tion
Each Device has a Unique 64-Bit Serial C ode
Stored i n an On-Board ROM
Multidrop Capability Simplifies Distributed
Temperature S ensing App lications
Requi res No External Compone nts
Can Be Powered from Data Line. Power
Supply Range is 3.0V to 5.5V
Measures Temperat ur es from -55°C to
+125°C (-67°F to +257°F)
±0.5°C Accuracy from -10°C to +85°C
9-B it Thermome ter Resolu tion
Converts Temperat ure in 750ms (max)
User-Definable Nonvolatile (NV) Alarm
Settings
Alarm Search Command Identifies and
Addresses Devices Who se T emperature is
Outside Programmed Lim its (T emperature
Al a rm C ondition )
Applications Include Thermostatic Controls,
Industrial Systems, Consumer Prod u cts,
PIN CONFIGURATIONS
DS1820
(DS18S20)
DD
(DS18S20Z)
DS1820
Thermometers, or Any Therma lly Sensit ive
System
DESCRIPTION
The DS18S20 digital thermometer provides 9-bit Celsius temperature measurements and has an alarm
function with nonvolatile user-programmable upper and lower trigger points. The DS18S20
communicates over a 1-Wire bus that by definition requires only one data line (and ground) for
communicat ion with a ce ntral micro pro cessor. It has an op erat ing temperat ure r ange of –55°C to +125°C
and is ac curat e to ±0.5°C over the range of –10°C to +85°C. In additio n, the DS18S20 can der ive power
directly from the data line (“parasite power”), eliminating the need for an external power supply.
Each DS18S20 has a unique 64-bit serial code, which allows multiple DS18S20s t o fu nc tion on t he s a me
1-Wire bus. Thus, it is simple to use one microprocessor to control many DS18S20s 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
contro l systems.
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DS18S20
PART
TEMP RANGE
PIN-PACKAGE
DS18S20
–55°C to +125°C
3 TO-92
DS18S20+
–55°C to +125°C
3 TO-92
DS18S20/T&R
–55°C to +125°C
3 TO-92 (2000 Piece)
DS18S20+T&R
–55°C to +125°C
3 TO-92 (2000 Piece)
DS18S20-SL/T&R
–55°C to +125°C
3 TO-92 (2000 Piece)*
DS18S20-SL+T&R
–55°C to +125°C
3 TO-92 (2000 Piece)*
DS18S20Z
–55°C to +125°C
8 SO
DS18S20Z+
–55°C to +125°C
8 SO
DS18S20Z/T&R
–55°C to +125°C
8 SO (2500 Piece)
DS18S20Z+T&R
–55°C to +125°C
8 SO (2500 Piece)
Data Input/Output. Open-dr ain 1-Wire interface pin. Also provides
Powering the DS18S20 section.)
Op tional VDD. VDD must be grounded for oper at ion in parasite
power mode.
1, 2, 6, 7,
ORDERING INFORMATION
+Denotes a lead(Pb)-free/RoHS-compliant package. A “+” appears on the top mark of le ad(Pb)-fr e e pac k a ges .
T&R = Tape and reel.
*TO-92 pack ages in ta pe and re el ca n be or der ed w ith s tra ight or fo rme d lea ds. Ch oos e “SL ” for s tra ight lea ds. B ulk TO -92 or de rs ar e s traigh t
leads only.
PIN DESCRIPTION
PIN
TO-92 SO
NAME FUNCTION
1 5 GND Ground
2 4 DQ
power to the device whe n used in parasite power mode (see the
3 3 VDD
—
8
N.C. No Connection
OVERVIEW
Figure 1 shows a block d iagram of the DS18S20, and pin descriptions are given in the Pin Description
table. The 64-bit RO M st ores the device’s un ique serial code. The scrat chpad memory contains t he 2 -byte
temperature r egister t hat stores t he digital ou tp ut from the te mperatur e sensor . In addition, t he scratchpad
provides access t o the 1-byte upper and lower alarm trigger registers (TH and TL). The TH and TL registers
are nonvolatile (EEP ROM), so they will retain data when the device is powered do wn.
The DS18S20 uses Maxim’s exclusive 1-Wire bus protocol that implement s bus communicat ion using
one control signal. The cont rol line requires a weak pullup res istor since all dev ices are linked to t he bus
via a 3-state or open-drain port (the DQ pin in the case of the DS18S20). In this bus system, the
microprocesso r (the master dev ice) identifies and addresses devices on the bus using each device’s unique
64-bit code. Because each device has a unique co de, the number of devices t hat 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 DS18S20 is the ability to operate without an external power supply. Power is
instead supplied through the 1-Wire pullup resist or via the DQ pin when the bus is high. The high bus
signal also charge s an internal capacito r (CPP), whic h the n sup plie s po wer to the de vic e whe n the bus is
low. This method of deriving power from the 1-Wire bus is referred to as “parasite power.” As an
alt ernative , t he DS1 8S20 may als o be p owe red by an e xternal supply on VDD.
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DS18S20
CPERCOUNT
REMAINCOUNTCPERCOUNT
READTEMPETEMPERATUR
__
___
25.0_
−
+−=
VPU
64-BIT ROM
DQ
VDD
INTERNAL VDD
CPP
PARA SITE POWER
CIRCUIT
MEMORY CONTROL
LOGIC
8-BIT CRC GENERATOR
TEMPER ATUR E SENS OR
ALARM HIGH TRIGGER (TH)
ALARM LOW TRIGGER (TL)
GND
DS18S20
Figure 1. DS18S20 Block Diagram
4.7k
POWERSUPPLY
SENSE
AND
1-Wire PORT
SCRATCHPAD
REGISTER (EEPROM)
REGISTER (EEPROM)
OPERATION—MEASURING TEMPERATURE
The core funct ionality of the DS18S20 is its direct -to-digital temperatu re sensor. The t emperature sensor
out put has 9-bit resolution, which corresponds to 0.5°C steps. The DS18S20 powers-up in a lo w-power
idle stat e; to initiat e a t emperat ure measurement and A-to-D co nver s ion, the mast e r mu st issu e a Co nve rt
T [44h] command. Following the conversion, the resulting thermal data is stored in the 2-byte
temperature r egister in the scrat chpad memory a nd the DS18S20 returns to its idle state. If the DS18S20
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 DS18S20 will respond by transmitting 0 while the
temperature conversion is in progress and 1 when the convers io n is do ne. If the DS18S20 is power ed wit h
parasite power , this notification technique cannot be used since the bus must be pulled high by a strong
pullup during the entire temperatur e co nversion. T he bus requirements for par asite power are explained in
detail in the Powering the DS18S20 section.
The DS18S20 output d ata is calibrat ed in degrees cent igrade; for Fa hrenheit appl ications, a lookup t able
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 po sitive or negative: for positive nu mbers S = 0 and for negative numbers S = 1. Table 1
gives examples of digital output data and the corresponding temperature reading.
Resolutions great er t han 9 bit s can be ca lculat ed using t he dat a fro m the t e mperature, COUNT RE MAIN
and COUNT PER °C registers in the scratchpad. Not e that the COUNT PER °C register is hard-w ire d t o
16 (10h). After reading the scratchpad, the TE MP_R EAD va lue is obt ained by t runcat ing t he 0. 5°C b it
(bit 0) from the temperature data (see Figure 2). The extended resolution temperature can then be
calculated using the fo llowing equation:
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