DS18B20 - Maxim - Pdf.Support

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.maximintegrated.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

t hat by definition r equire s only one dat a 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

add it io n, t he DS18B20 can derive power directly

fro m t he data line ( “parasite power ”), eliminat ing

t he need fo r an exter nal power supply.

Each DS18B20 has a unique 64-bit serial code,

which allows multiple DS18B20s to function on

t he same 1-Wire bu s. T h u s , it is s imple 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

S tor e d i n a n O n-Board ROM

 Multidrop Capability Simplifies Distributed

Temperature-Se nsing App licat io ns

 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 D igita l 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 T hermostat ic Controls,

Industrial Systems, Consumer Products,

Thermometers, or Any Thermally Sensitive

System

PIN CONFIGURATIONS

DS18B20

Programmable Resolution

Wire Digital Thermometer

TO-92

(DS18B20)

(BOTTOM VIEW)

MAXIM

18B20

GND

SO (150 mil s)

(DS18B20Z)

N.C.

GND

N.C.

MAXIM

18B20

N.C.

GND

N.C.

18B20

µSOP

(DS18B20U)

1-Wire is a registered trademark of M axim Integr at ed P ro ducts , Inc .

DS18B20

2 of 22

ORDERING INFORMATION

PART

TEMP RANGE

PIN-PACKAGE

TOP MARK

DS18B20

-55

C to +125

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

3 TO-92 (2000 Piec e) *

18B20

DS18B20-SL+T&R

-55°C to +125°C

3 TO-92 (2000 Piec e) *

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

SOP (3000 Piece)

18B20

DS18B20U+T&R

-55

C to +125

SOP (3000 Piece)

18B20

DS18B20Z

-55

C to +125

8 SO

DS18B20

DS18B20Z+

-55°C to +125°C

8 SO

DS18B20

DS18B20Z/T&R

-55

C to +125

8 SO (2500 Piece)

DS18B20

DS18B20Z+T&R

-55°C to +125°C

8 SO (2500 Piece)

DS18B20

+Denotes a lead-free p ac k age . A “+” will appear on the top mark of lead-free packages.

T&R = Tape and reel.

*TO-92 packages in tape and r ee l c an b e or der ed w it h stra ig ht or f orme d lea ds. C hoos e “SL” f or stra ig ht leads. Bu lk TO -9 2 orde rs are s tra ight

leads only.

PIN DESCRIPTION

PIN NAME FUNCTION

SOP TO-92

1, 2, 6,

7, 8 2, 3, 5,

6, 7 — N.C. No Connect ion

3 8 3 VDD O p tio n al VDD. VDD must be gro unded fo r operatio n in

paras ite power mode.

4 1 2 DQ Data Inp ut/O utput. Ope n-drain 1-Wire inter face pin. Also

pro vides power to t he device w hen 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 RO M stor es t he device’s unique serial co d e. The scratchpad me mory conta ins t he 2 -byte

t emper at ure reg ist er t hat stor es t he d ig it al o ut put from the te mperat ur e sensor . In add itio n, t he scrat chpad

provides access to the 1-byte upper and lower alarm trigger registers (TH and TL) and the 1-byte

configuration reg ister . The configurat io n register allows t he user to set the resolut ion o f the temperature-

to-digital conversion to 9, 10, 11, or 12 bits. The TH, TL, and configuration registers are nonvolatile

(E E P ROM), so the y w ill retain data when the device is powered dow n.

The DS18B20 uses Maxim’s exclusive 1-Wire bus protocol that implements bus communication using

one co ntrol sig na l. The control line require s 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

micro p ro cesso r (the mast er dev ice) identifies and addr esses de vice s on the bus using each device’s uniqu e

64-bit code. Because each device has a unique code, the number o f devices that can be addressed on o ne

DS18B20

3 of 22

bus is virt ually u nlimited. The 1-Wire bus protocol, including detailed exp lanat ions of the command s and

“t ime slots,” is covered in the 1-Wire Bus Syst e m 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 (CPP), whic h then supplies po wer to the device w hen the bus is

low. This method of deriving power from the 1-Wire bus is referred to as “parasite power.” As an

alt e rna tive, the DS1 8B2 0 may als o be powere d by a n external suppl y on VDD.

Figure 1. DS18B20 Block Diagram

OPERATION—MEASURING 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, r espect ive ly. T he de fau lt resolution at po wer -up is 12-bit . T he DS18B20

powers up in a low-power idle state. To initiate a temperature measurement and A-to-D co nversio n, 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 B us S yst em sect io n) after t he Convert T command and t he DS18B20 will respond by tr ans mitt ing

0 while the te mperature convers io n is in progress and 1 whe n t he co nvers io n is do ne. If the DS18B20 is

power ed with para s ite power, t his not ificatio n technique cannot be used since the bus must be pulled high

by a st r ong pu llup du r ing t he e nt ir e t emperat ure co nver sio n. T he bus requ irement s for p arasite po wer ar e

explain e d in detail in the Powering the DS18B20 section.

The DS18B20 output temperature data is calibrated in degrees Celsius; for Fahrenheit applications, a

lo o kup t able or co nversio n ro utine must be used. T he temp erat ur e dat a is st o red as a 16-b it 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

co rresponding temperature read ing for 1 2-bit r esolutio n c onversions.

4.7k

POWER-

SUPPLY

SENSE

64-BIT ROM

AND

1-Wire PORT

VDD

INTERNAL V

CPP

PARASITE POWER

CIRCUIT

MEMORY CONTROL

LOGIC

SCRATCHPAD

8-BIT CRC GENERATOR

TEM PERATURE SEN S OR

ALARM HIGH TRIGGER (T

)

ALARM LOW TRIGGER (T

)

CONFIGURATION REGISTER

(EEPROM)

GND

DS18B20

4 of 22

Figure 2. Temper atu re Register Form at

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

L S BYTE 23 22 21 20 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 26 25 24

S = SIGN

Table 1. Temperature/Data Relationship

TEMPERATURE (

C) DIGITAL OUTPUT

(BINARY) DIG ITAL 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.

OPERATION—ALARM 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-byt e TH and TL registers (see Figure 3).

The s ig n bit ( S) ind ic ate s if the va lu e is po s itive o r negative: for positive number s S = 0 and for negat ive

numbers S = 1. The TH and TL registers are nonvolatile (EEPROM) so they will retain data when the

device is po wered do wn. T H and T L can be acces sed t hrough byt e s 2 and 3 of the scrat chpad as e xplained

in the Memory section.

Figure 3. TH and TL Register Format

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

S 26 25 24 23 22 21 20

Only bits 11 t hrough 4 o f t he t emperatur e register ar e used in t he TH a nd T L co mpar ison sinc e TH a nd TL

are 8-bit r egist ers. I f t he measured t e mp erat ure is lo wer than or eq ual to T L or higher t han or equa l t o TH,

an alarm condition exists and an alarm flag is set inside the DS18B20. This flag is updated after every

temperature measure me nt ; t here for e, if the alarm c onditio n go es away, the flag w ill be t u r ned o ff after the

next temperature conversi on.

DS18B20

5 of 22

The mast er dev ic e can check t he a larm flag status of all DS18B20 s on t he bus by issuing an Alarm Searc h

[ECh] co mmand. Any DS18B20s with a set alarm flag will respond to the command, so the master ca n

determine exactly which DS18B20s have experienced an alarm condition. If an alarm condition exists

and the TH or TL settings have changed, another temperature conversion should be done to validate the

alarm condition .

POWERING THE DS18B20

The DS18B20 can be powered by an external supp ly on the VDD pin, or it can oper ate in “paras ite power”

mode, which allows the DS18B20 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 DS18B20’s parasite-power control circuitry, which “steals” power from the 1-Wire

bus via the DQ p in when t he bus is hig h. The stolen charge powers the DS18B20 while the bus is high,

and so me o f t he c har ge is stored o n t he par asit e po wer capacitor (CPP) to provide power whe n t he bus is

low. When t he DS18B20 is us ed in parasit e p ower mode, the VDD pin must be connect ed to ground.

In parasit e power mode, the 1-Wire bus a nd CPP c an pro vide sufficient current to t he DS18B20 for most

operations as long as the specified timing and voltage requirements are met (see the DC Electrical

Characteristics and AC Electrical Characteristics). However, when the DS18B20 is performing

t emper at ure convers ions o r copying data fro m the scrat chpad me mo r y to EEP ROM, the o perating cur rent

can be as high as 1.5mA. This current can cause an unacceptable voltage drop across the weak 1-Wire

pullup resistor and is mo re curr ent than can be sup plied by C PP. T o assure that t he DS18B20 has suf ficie nt

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 mu st be sw it c hed to the strong pullup w it hin 1 0µs (max) aft er a Convert T [44h] or Co py Scratchpa d

[48h] command is issued, and the bus must be he ld high by the pu llup for t he durat ion of the conversion

(tCONV) or data transfer (t WR = 10ms). No other activ ity ca n t ake place on t he 1-Wire bus while t he pullup

is enabled.

The DS18B20 can also be powered by the co nvent ional method o f connect ing an externa l power supp ly

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

requir ed , and t he 1-Wire bus is free t o car r y other traffic during the temperat ur e convers io n t ime.

The use of parasite power is not recommended for temperatures above +100°C since the DS18B20 may

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

temperatures. For app licat io ns in whic h such t emperat ur es are likely, it is stro ngly recommended tha t t he

DS18B20 be powered by an ext ernal power supply.

In so me situat ions the bus master may not know whet her the DS18B20 s on the bus are parasite power ed

o r powered by e xte rna l su pp lies. The mast er need s t his info r mat io n t o det ermine if t he st ro ng bus p u llup

should be used during temper ature conversions. To get this info rmation, the mast er can issue a Sk ip RO M

[CCh] command followed by a Read Power Supply [B4h] command followed by a “read time slot”.

During the read time slot, parasite powered DS18B20s will pull the bus low, and externally powered

DS18B20s will let t he bus remain high. I f t he bus is pu lled lo w, t he master knows t hat it must supply t he

strong pullup on t he 1-Wire bus dur ing temper ature co nversions.

DS18B20

6 of 22

Figure 4. Supplying the Parasite-Powered DS18B20 During Temperature Conversions

Figure 5. Powering the DS18B20 with an External Supply

64-BIT LASERED ROM CODE

Each DS18 B20 conta ins a unique 64–bit code (see Figure 6) stored in ROM. T he least s ig nificant 8 bit s

of the ROM code contain the DS18B20’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 fro m t he first 56 bit s of the ROM code. A detailed explanat io n o f the CRC bits is provide d in

the CRC Generation sect io n. T he 64-bit RO M cod e and a ssoc iat ed ROM funct io n cont ro l lo gic a llo w t he

DS18B20 to o perate as a 1-Wir e d evice using t he protocol detailed in t he 1-Wire B us System section.

Figure 6. 64-Bit Lasered ROM Code

8-BIT CRC

48-BIT SERIAL NUMBER

8-BIT FAMI LY CODE (28h)

MSB

LSB

MSB

4.7k

1-Wire BUS

DS18B20

GND

TO OTHER

1-WIRE DEVICES

(EXTER NAL SUPPL Y)

DS18B20

GND

4.7k

TO O T HER

1-WIRE DEVICES

1-Wi re BUS

DS18B20

7 of 22

MEMORY

The DS18B20’s memory is organized as shown in Figure 7. The memory consists of an SRAM

scratchpad with nonvolatile EEPROM storage for the high and low alarm trigger registers (TH and TL)

and configuration register. Note that if the DS18B20 alarm function is not used, t he TH and TL registers

can serve as general-purpose memory. All memory commands are described in detail in the DS18B20

Function Commands section.

Byte 0 and byte 1 of the scratchpad contain the LSB and the MSB of the temperature register,

respectively. These bytes are read-only. Bytes 2 and 3 provide access to TH and TL registers. Byte 4

co nt ains t he co nfiguration reg ister d ata, which is explained in det ail in t he Configuration R egister section.

Bytes 5, 6 , and 7 are r eserved for interna l use by the dev ice and ca nno t be o verwritten.

Byte 8 of the scr atchpad is read-on ly a nd contain s the CRC code fo r byt es 0 t hro ugh 7 o f the scratchpad.

The DS18B20 generat es t his CRC using the method descr ibed in the CRC Generation section.

Dat a is writt en to b yt es 2, 3, and 4 of the scratchpad u s ing the Write Scratchpad [4Eh] co mmand; t he data

must be transmitted to the DS18B20 starting with the least significant bit of byte 2. To verify data

integrity, the scratchpad can be read (using the Read Scratchpad [BEh] command) after the data is

written. When reading the scratchpad, data is transferred over the 1-Wire bus starting with the least

significant bit of byte 0. To t ransfer t he TH, TL and configuration dat a from t he scrat chpad to EEPROM,

t he master must issue t he Cop y Scr atchpad [48h] command.

Data in the E EPROM reg ist ers is ret ained when the device is powered down; at power-up t he EEPROM

dat a is re lo ad ed int o t he corr espo nd ing scrat chpad locat ions. Dat a can also be reloaded from EEPROM to

the scratchpad at any time using the Recall E2 [B8h] command. The master can issue read time slots

following the R ec all E 2 command a nd the DS18B20 w ill ind icat e the status o f the rec all by transm itt ing 0

while the rec all is in pro gress and 1 when the r ecall is done.

Figure 7. DS18B20 Memory Map

SCRATCHPAD

(POWER-UP STATE)

Byte 0 Temper ature LSB (50h)

Byte 1 T emperat ur e MSB (05h) EEPROM

Byte 2 TH Reg ister o r User B yte 1* TH Reg ister o r User B yte 1

Byte 3 TL Reg ist er o r User Byt e 2 * TL Reg ist er o r User Byt e 2

Byte 4 Configurat ion Regist er * Co nfiguration Reg ist er

Byte 5 Reserved (FFh)

Byte 6 Reserved

Byte 7 Reserved (10h)

Byte 8 CRC*

Power-up state depends on value(s) stored in EEPROM.

(85°C)

DS18B20

8 of 22

CONFIGURATION REGISTER

Byte 4 o f the scrat chpad me mory co ntains the configurat io n reg ist er, whic h is or ganized as illustrated in

Figure 8. The user can set the conversion resolution of the DS18B20 using the R0 and R1 bits in this

reg ister as shown in Table 2. The pow er-up defau lt o f t hese bit s is R0 = 1 and R1 = 1 (12-b it re s olution ) .

Note that there is a direct tradeoff between resolution and conversion time. Bit 7 and bits 0 to 4 in the

co nfiguration reg ister are reserved for inter nal use by the devic e and ca nno t be o verwritten.

Figure 8. Configuration Register

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0 R1 R0 1 1 1 1 1

Table 2. Thermometer Resolution Configuration

R1 R0 RESOLUTION

(BITS) M AX CO NVERSION

TIME

0 0 9 93.75ms (tCONV/8)

0 1 10 187.5ms (tCONV/4)

1 0 11 375ms (tCONV/2)

1 1 12 750ms (tCONV)

CRC GENERATION

CRC byt es are pro vided as part of t he DS18B20’s 64-bit ROM co de and in the 9th byt e o f the scrat chpad

memo ry. The ROM code CRC is calcu lat ed fr om the first 5 6 b it s of t he ROM cod e and is co nt ained in t he

most significant byte of the ROM. The scratchpad CRC is calculated from the data stored in the

scrat chpad, and there fore it changes when t he data in t he scrat chpad changes. The CRCs pro vide t he bu s

master with a method of data validation when data is read from the DS18B20. To verify that data has

been read correctly, the bus master must re-calculate the CRC from the received data and then compare

t his value t o either t he ROM code CRC ( for ROM r eads) or to the scrat chpad C RC (for scr atchpad reads).

If the calculated CRC matches the read CRC, the data has been received error free. The comparison of

CRC values and the decision to continue with an operation are determined entirely by the bus master.

There is no circuitry inside the DS18B20 that prevents a command sequence from proceeding if the

DS18B20 CRC (ROM o r scratchpad) does not match the value g enerated by the bus master .

T he equivalent p olynomial func tion of the C R C ( R OM or s cratchpad) is:

CRC = X8 + X5 + X4 + 1

The bus master can re-ca lculat e t he CRC a nd co mpare it to the CRC values fr o m the DS18B20 using t he

po lyno mial generator shown in Figure 9. This circuit consists of a shift register and XOR gates, and the

shift register bits are init ialized to 0. Starting wit h the least significant bit of the ROM code or t he lea st

significant bit of byte 0 in the scratchpad, one bit at a time should shifted into the shift register. After

shifting in the 56th bit from the ROM or the most significant bit of byte 7 from the scratchpad, the

po lynomial generator will contain the re-calculated CRC. Next, the 8-bit ROM code or scratchpad CRC

fr om t he DS18B20 must be shifted into t he cir cuit . At this point, if the re-calculated CRC w as correct , t he

sh ift regis te r w ill c ontain all 0 s . Additional inform a tion abou t the Maxim 1-Wir e cyclic redundancy check

DS18B20

9 of 22

is available in Application Note 27: Understanding and Using Cyclic Redundancy Checks with Maxim

iButton Products.

Figure 9. CRC Generat or

1-WIRE BUS SYSTEM

The 1-Wire bus system uses a single bus master to control one or more slave devices. T he DS18B20 is

always a slave. When there is only one slave on the bus, the system is referred to as a “single-drop”

s ys tem; the system is “ multidr op” if t here ar e multiple slave s on t he bus.

All d ata and commands are t r ansmitted least sig n if ica nt bit first over the 1-Wire bus.

The following discussion of the 1-Wire bus system is broken down into three topics: hardware

co nfiguration, t r ansactio n sequence , and 1-Wire signaling (signal type s and timing).

HARDWARE CONFIGURATION

The 1-Wire bus has by definition only a single data line. Each device (master or slave) interfaces to the

data line via an open-drain or 3-state port. This allows each device to “release” the data line when the

device is not transmitt ing dat a so t he bu s is ava ilable for use by ano ther de vice. The 1-Wire port of the

DS1 8B2 0 (the DQ pin) is open dr ain with an internal circ uit e quivalent t o that show n in Figure 10.

The 1-Wire bus requires an external pullup resistor of approximately 5kΩ; thus, the idle state for the

1-Wire bu s is hig h. I f for any reason a transaction need s to be suspended, the bus MUST be left in t he idle

state if the transaction is to resume. Infinite recovery time can occur between bits so long as the 1-Wire

bus is in the inact ive ( high) st ate during the reco very period. If the bus is held low for more t han 4 80µs,

all comp onents on the bus will be reset.

Figure 10. Hardware Configuration

(MSB)

(LSB)

XOR

INPUT

4.7k

5μA

TYP

DS18B20 1-Wire PORT

100

Ω

MOSFET

Rx = RECEIVE

Tx = TRA NSMIT

1-Wire BUS

DS18B20

10 of 22

TRANSACTION SEQUENCE

The t r ansaction sequence for access ing the DS18B20 is as follows:

S tep 1. Initialization

S tep 2. ROM Command (followed b y an y required data exchange)

S tep 3. DS18B20 Funct io n Co mma nd (fo llo wed by a ny required dat a exchange)

It is very i mpo r tant to fo llow t h is sequence every t i me t he DS18B20 is a cces sed, as the DS18B20 will no t

respond if any steps in the sequence are missing or out of order. Exceptions to this rule are the Search

ROM [F0h] and Alarm Search [ECh] commands. After issuing either of these ROM commands, the

mast er must ret urn to St ep 1 in the sequence.

INITIALIZATION

All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence

consists of a reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the

sla ve(s). T he presence pulse let s the bu s ma ster know t hat sla ve de vice s (such as the DS18 B20) ar e o n t he

bus a nd are read y t o o perate. Timing for t he re set and presence pu lses is det ailed in t he 1-Wire Signaling

section.

ROM COMMANDS

After the bus master has detected a presence pulse, it can issue a ROM command. These commands

operate on the unique 64-bit ROM codes o f each slave dev ice and a l lo w the ma ster to single out a specific

device if many are present on the 1-Wire bus. These co mmands also allow the master to determine how

many and what types of devices are present on the bus or if any device has experienced an alarm

condition. There are five ROM commands, and each command is 8 bits long. The master device must

issue an appropriate ROM command before issuing a DS18B20 function command. A flowchart for

op e ratio n of t he RO M comman ds is show n in Figure 11.

SEARCH ROM [F0h]

When a system is initially powered up, the master must identify the ROM codes of all slave devices on

the bus, which allows the master to determine the number of slaves and their device types. The master

learns t he ROM codes t hro u gh a pro cess o f elimination that r equ ires the ma ster to per for m a Search RO M

cycle ( i. e. , Sear ch ROM co mmand fo llo wed b y d at a exchange) as many t imes as neces sar y t o ide nt ify al l

of t he slave devices. If t here is only one slave on the bu s, t he simpler Read ROM co mmand (s ee below)

can be used in place of the Search ROM process. For a detailed explanation of the Search ROM

procedure, refer to the iButton® Book of Standards at www.maxim-ic.com/ibuttonbook. After every

Search ROM cyc le, the bu s mast er must return to St ep 1 (Initialization) in the t r ansaction sequence.

READ ROM [33h]

This co mma nd ca n o nly be used w hen t here is o ne s lave o n t he bu s. It allo w s t he bus ma st er to read t he

s lave ’s 64-bit ROM code without using the Searc h ROM procedure. I f t his co mma nd is u se d w he n t her e

is more than one slave present on the bus, a data collision will occur when all the slaves attempt to

respond at the same time.

MATCH ROM [55h]

The match ROM co mmand follo wed by a 64-bit ROM co de sequence a llo ws t he bus mast er to address a

specific slave device on a multidrop or single-drop bus. Only the slave that exactly matches the 64-bit

ROM code sequence will respond to the funct ion command issued by t he mast er; all other slaves on t he

bus will wa it fo r a reset pulse.

iButton is a registered trademark of M axim Int eg r at ed Prod uc t s , Inc .

DS18B20

11 of 22

SKIP ROM [CCh]

The master can use this command to address all devices on the bus simultaneously without sending out

any ROM code information. For example, the master can make all DS18B20s on the bus perform

simult aneous te mperature conversio ns by issuing a Skip ROM co mmand fo llo wed by a Convert T [44h]

command.

Note that the Read Scratchpad [BEh] command can follow the Skip ROM command only if there is a

single slave device on the bus. In this case, time is saved by allowing the master to read fro m the slave

without sending the device’s 64-bit ROM code. A Skip ROM command followed by a Read Scratchpad

co mmand will cause a data collision on the bus i f there is more than o ne s la ve s in c e mu ltip le d e vic e s w i l l

attempt to transmit data sim ul tan eously.

ALARM SEARCH [ECh]

The operation of this command is identical to the operation of the Search ROM command except that

only slaves wit h a set alarm flag will respond. This command allows the master device to determine if

any DS18B20s experienced an alarm condition during the most recent temperature conversion. After

every A lar m Searc h cycle ( i. e., Alar m Sear ch co mmand fo llo wed by d at a exchange), t he bus mast er must

return to Step 1 (Initialization) in the transaction sequence. See the Operation—Alarm Signaling section

fo r an exp la nation of alar m flag op er ation.

DS18B20 FUNCTION COMMANDS

After the bus master has used a ROM command to address the DS18B20 with which it wishes to

co mmu nicat e, t he master can issue o ne o f the DS 18B20 fu nct io n commands. T hese co mmands a llo w t he

mast er to write to and read from the DS18B20’s sc r atchpad me mory, initiat e temperatur e conversions an d

determine the power supply mode. The DS18B20 function commands, which are described below, are

su mma r iz ed in Table 3 and il lus trate d by the flo wchart in Figure 12.

CONVERT T [44h]

This co mmand init iates a single temperat ure co nversion. Followin g t he co nvers io n, t he resu lt ing the r ma l

dat a is sto red in the 2-byt e t e mper at ure reg ist er in t he scrat chpad me mo r y and t he DS18 B20 ret urns to it s

low-power idle state. If the device is being used in parasite power mode, within 10µs (max) after this

command is issued the master must enable a strong pullup on the 1-Wire bus for the duration of the

co nvers io n ( t CONV) as described in t he Powering the DS18B20 section. If the DS18B20 is powered by an

exte r na l s up p l y, t he master can issue r ead t ime s lot s after the C o nve r t T c o mma nd a nd t he DS 1 8B 20 w ill

respo nd by transmitt ing a 0 while the temperat ure co nversio n is in pro gress and a 1 w hen t he co nve rsio n

is done. In paras it e power mo de this not ificatio n t echnique c annot be used since the bus is pulled high by

the stro ng pullup during t he convers ion.

WRITE SCRATCHPAD [4Eh]

This comma nd a llow s the mast er to wr ite 3 bytes o f data to t he DS18 B20’s scr atchpad. T he first d ata byt e

is written into the TH register (byte 2 of the scratchpad), the second byte is written into the TL register

(byte 3), and the third byte is written into the configuration register (byte 4). Data must be transmitted

least significant bit first. All three bytes MUST be written before the master issues a reset, or the data

may be corrupted.

READ SCRATCHPAD [ BEh]

This co mmand a llo ws the ma ster to read the content s o f t he scratchpad. The data transfer starts with the

least significant bit of byte 0 and continues through the scratchpad until the 9th byte (byte 8 – CRC) is

read. The master may issue a reset t o terminate reading at any t ime if only part of the scrat chpad d at a is

needed.

DS18B20

12 of 22

COPY SCRATCHPAD [48h]

This co mmand cop ie s the co nt ents o f t he scr at chp ad TH, TL and configur at io n registers (byt e s 2, 3 and 4)

to EEPROM. If the device is being used in para s ite power mode, within 10µs (max) after this command is

issued the master must enable a strong pullup on the 1-Wire bus for at least 10ms as described in the

Powering the DS18B20 section.

RECALL E2 [B8h]

This command recalls the alarm trigger values (TH and TL) and configuration data from EEPROM and

places the data in bytes 2, 3, and 4, respect ive ly, in the scrat chpad me mo ry. The ma ster device can issue

read t ime slot s follo wing the Recall E2 co mmand and the DS18B20 will ind icat e the statu s of the recall by

transmit ting 0 while the recall is in progress and 1 when the re ca ll is done. The re call operat ion happens

auto mat ica lly at power-up, so valid dat a is available in the scratchpad as soo n as po wer is app lied to t he

device.

READ POWER SUPPL Y [B4h]

The master device issues t his comma nd followed by a read time slot to determine if any DS18B20s on the

bus are using parasite power. During the read time slot, parasite powered DS18B20s will pull the bus

low, and externally powered DS18B20s will let the bus remain high. See the Powering the DS18B20

section for usage information for t his co mmand.

Table 3. DS18B20 Function Command Set

COMMAND DESCRIPTION PROTOCOL

1-Wire BU S

ACTIVITYAFTER

COMMAND IS ISS UED

NOTES

TEMPERATURE CONVERSION COM MANDS

Convert T

Initi ates temperature

conversion. 44h

DS18B20 transmit s

co nversion status to master

(not app licable for par asite-

power ed DS18B20s).

MEMORY COMM ANDS

Read

Scratchpad

Reads t he ent ire scrat chpad

includ ing the CRC byte.

BEh

DS18B20 transmit s up to 9

dat a b ytes to master .

Write

Scratchpad

Writ es data int o scratchpad

bytes 2, 3, and 4 (TH, TL,

and configuratio n

registers).

4Eh

Master t r ansmits 3 data bytes

to DS18B20. 3

Copy

Scratchpad

Copies T

, T

, and

co nfiguration reg ister dat a

from the scrat chpad to

EEPROM.

48h

None

Recal l E

Recal ls T

, T

, a nd

co nfiguration reg ister dat a

from EEPROM to the

scratchpad.

B8h

DS18B20 transmit s reca ll

sta tus to master.

Read Power

Supply

S ig nals DS18B20 po wer

supply mo d e to the ma ster. B4h

DS18B20 transmit s suppl y

sta tus to master.

Note 1:

For par a sit e-powered DS18B20s, th e ma ster must enable a strong pullup on the 1-Wire bus during temperat ure

conversi ons a nd c opi es from t he s cratch pa d to EEPRO M. N o other bus activity may take place during this time.

Note 2:

The master can interrupt the transmission of data at any time by issuing a reset.

Note 3:

All three bytes must be written before a reset is issued.

DS18B20

13 of 22

Figure 11. ROM Commands Flowchart

CCh

SKIP ROM

COMMAND

MASTER TX

RESET PULSE

DS18B20 T

PRESENCE

PULSE

MASTER T

ROM

COMMAND

33h

READ ROM

COMMAND

55h

MATCH ROM

COMMAND

F0h

SEARCH ROM

COMMAND

ECh

ALARM SEARCH

COMMAND

MASTER TX

BIT 0

DS18B20 T

BIT 0

DS18B20 TX BIT 0

MASTER TX BIT 0

BIT 0

MATCH?

MASTER T

BIT 1

MATCH?

BIT 63

MATCH?

MASTER TX

BIT 63

N N

DS18B20 T

BIT 1

DS18B20 T

BIT 1

MASTER TX BIT 1

DS18B20 TX BIT 6 3

DS18B20 T

BIT 63

MASTER TX BIT 63

BIT 0

MATCH?

BIT 1

MATCH?

BIT 63

MATCH?

DS18B20 T

FAMILY CODE

1 B YTE

DS18B20 TX

SERIAL NUMBER

6 BYTES

DS18B20 TX

CRC BYTE

DS18B20 TX BIT 0

MASTER TX BIT 0

DEVICE(S)

WITH ALARM

FLAG SET?

Initialization

Sequence

MASTER T

FUNCTION

COMMAND

(FIGURE 12)

DS18B20

14 of 22

Figure 12. DS18B20 Function Command s Flowchart

MASTER TX

FUNCTION

COMMAND

44h

CONVERT

TEMPERATURE

PARASITE

POWER

DS18B20 BEGINS

CONVERSION

DEVICE

CONVERTING

TEMPERATURE

MASTER

RX “0s”

MASTER

RX “1s”

MASTER ENABLES

STRONG PULLUP ON DQ

DS18B 20 CONVERTS

TEMPERATURE

MASTER DISABLES

STRONG PULLUP

48h

COPY

SCRATCHPAD

PARASITE

POWER

MASTER ENABLES

STRONG PULL-

UP ON DQ

DATA COPIED FROM

SCRATCHPAD TO EEPROM

MASTER DISABLES

STRONG PULLUP

MASTER

RX “0s”

COPY IN

PROGRESS

MASTER

“1s”

RETURN TO INITIALIZA TION

SEQUENCE (FIGURE 11) FOR

NEXT TRANSACTION

B4h

READ

POWER SUPPLY

PARASITE

POWERED

MASTER

RX “1s”

MASTER

RX “0s”

MASTER TX TH BYTE

TO SCRATCHPAD

4Eh

WRITE

SCRATCHPAD

MASTER TX TL BYTE

TO SCRATCHPAD

MASTER T

CONFIG. BYTE

TO SCRATCHPAD

BEh

READ

SCRATCHPAD

HAVE 8 BYTES

BEEN READ

MASTER

TX RESET

MASTER R

DATA BYTE

FROM SCRATCHPAD

MASTER RX SCRATCHPAD

CRC BYTE

MASTER

RX “1s”

B8h

RECALL E2

MASTER BEGINS DATA

RECALL FROM E2 PROM

DEVICE

BUSY RECALLING

DATA

MASTER

RX “0s”

DS18B20

15 of 22

1-WIRE SIGNALING

The DS18B20 u ses a strict 1-Wire communication protocol to ensure data integrit y. Several signal types

are defined by this protocol: reset pulse, presence pulse, write 0, write 1, read 0, and read 1. The bus

maste r initiate s all these sig nals, with the except ion of the prese nce pulse.

INITIAL IZATION PROCEDURE—RESET AND PRESENCE PULSES

All communic ation with t he DS18 B20 begins with an init ia lizat io n sequenc e that co nsists of a reset pulse

fro m t he mast er fo llowed by a prese nce pu lse from the D S18B2 0. Th is is illu st rat ed in Figure 13. Whe n

the DS18B20 sends the presence pulse in response to the reset, it is indicating to the master that it is on

t he bus and read y to oper at e.

Dur ing t he init ializ at io n sequ e nce t he bus mast er tr ansmit s (T X) t he reset pu lse by pull ing t he 1-Wir e bu s

low for a minimum of 480µs. The bus master then releases the bus and goes into receive mode (RX).

When the bus is released, the 5kΩ pullu p res ist or pu lls t he 1-Wir e bus high. When the DS18B20 detects

this r ising edge, it wait s 15µs to 60µs and t hen transmit s a presence pulse by pulling the 1-Wire bu s low

for 60µs to 240µs.

Figure 13. In itialization Tim ing

REA D/WRITE TIME SLOTS

The bus master writes data to the DS18B20 during write time slots and reads data from the DS18B20

during read t ime slot s. One bit of dat a is t r ansmitted over t he 1-Wire bus p er time slo t.

WRITE TIME SLOTS

There are two types of write time slots: “Write 1” time slots and “Write 0” time slots. The bus master

uses a Wr ite 1 time slot to write a logic 1 to the DS18B20 and a Wr ite 0 time slot to write a logic 0 to the

DS18B20. All write time s lo ts must be a mini mum of 60µs in duration with a minimum of a 1µs recovery

t ime bet wee n in dividual w r it e s lo t s. Bo th types o f write t ime slot s are init iated by the master pulling t he

1-Wire bu s low ( se e Figure 14).

To generat e a Writ e 1 time slo t , a ft er pulling the 1-Wire bus lo w, t he bu s mast er must re leas e t he 1-Wire

bus within 15µs. When t he bus is released, t he 5kΩ pullup resistor will pull the bus high. To generate a

Writ e 0 time slo t, aft er pulling the 1-Wire bus lo w, t he bu s master must co ntinue to hold the bus low for

the duration of the time slot (at least 60µs).

LINE TYPE LEGEND

Bus master pulling low

DS 18B20 pulling low

Resi stor pu l lup

VPU

GND

1-WIRE BUS

480µs minimum

DS18B20 T

presence pulse

60-240

MASTER T

RESET PULSE

MASTER R

DS18B20

waits 15-60

DS18B20

16 of 22

The DS18B20 samples the 1-Wire bus during a window that lasts from 15µs to 60µs after the master

initiates t he write time slot. I f t he bus is high dur ing the sampling window, a 1 is wr it ten t o t he DS18B20.

If t he line is low, a 0 is writ ten to the DS18B20.

Figure 14. Read/Wr ite Time Slot Timin g Diagram

REA D TIME SLOTS

The DS18B20 can o nly tr ansmit d at a to the mast er when t he mast er issues read t ime s lo t s. T he refo r e , t he

master must generate read time slots immediately after issuing a Read Scratchpad [BEh] or Read Power

Supp ly [B4h] co mmand, so that the DS18B20 can pro vide t he request ed data. In add it io n, t he mast er ca n

generat e read t ime slot s a ft er issuing Co nvert T [44h] o r Reca ll E2 [ B8h] co mmands to find out the status

o f the op er ation as exp lained in the DS18B20 Function Commands section.

All read time slots must be a minimum of 60µs in duration with a minimum of a 1µs recovery time

between slots. A read time slot is initiated by the master device pulling the 1-Wire bus low for a

min imum of 1µs a nd t he n re le as ing the bus (see Figure 14). After t he master init iates the read t ime slo t,

t he DS18B20 will begin trans mit ting a 1 or 0 on bus. The DS18B20 t r ansmits a 1 by leaving the bus high

and t ransmits a 0 by pu lling the bus lo w. When transmit ting a 0, t he DS18B20 will re lease the bu s by the

end of the time slot, and the bus will be pulled back to its high idle state by the pullup resister. Output

15µs

GND

1-WIRE B US

60µs < T

“0” < 120µs

s < TREC < ∞

DS18B20 Samples

MIN TYP MAX

30µs

> 1

MASTER WRITE “0” SLOT

MASTER WRITE “1” SLOT

GND

1-WIRE B US

MASTER READ “0” SLOT

MASTER READ “1” SLOT

Master samples

START

OF SLOT

START

OF SLOT

> 1

s < TREC <

∞

15µs

DS18B20 Samples

MIN TYP MAX

LINE TYPE LEGEND

Bus master pulling low DS18B20 pull ing low

Resi stor pu l lup

> 1

DS18B20

17 of 22

data from t he DS18B20 is valid for 15µs a ft er t he fal ling edge t hat init iat ed t he read t ime s lo t . Therefo re,

t he master must r elease t he bus and the n samp le t he bus st ate wit hin 15µs fro m the start of the slot.

Figure 15 illustrates that the sum of TINIT, TRC, and TSAMPLE mu st be less than 15µs for a read time slot.

Figure 16 shows that system timing margin is maximized by keeping TINIT and TRC as short as possible

and by lo cating the master sample time dur ing read time slots tow ar ds the end of the 15µs perio d.

Figure 15. Detailed Master Read 1 Timin g

Figure 16. Recommended Master Read 1 Timing

RELATED APPLIC ATION NOTES

The following application notes can be applied to the DS18B20 and are available on our website at

www.maxim-ic.com.

Application Note 27: Understanding and Using Cyclic Redundancy Checks with Maxim iButton Products

Application Note 122: Using Dallas' 1-Wire ICs i n 1-Cell Li-Ion Battery Packs with L ow-Side N-Channel

Safety FETs Master

Application Note 126: 1-Wire Communication Through Soft ware

Application Note 162: Interfacing the DS18x20/DS1822 1-Wire Temperature Sensor in a Microcontroller

Environment

Application Note 208: Curve Fitting the E rror of a Bandgap-Based Digital Temperature Sensor

Application Note 2420: 1-Wire Communication with a Microchip PICmicro Microcontroller

Application Note 3754: Single-Wire Serial Bus Carries Isolated Power and Data

Sample 1-Wire subroutines that can be used in conjunction with Application Note 74: Reading and

Writing iButtons via Serial Interf aces can be downlo ad ed from the Maxim we b s ite.

GND

1-WIRE B US

15µs

VIH of Master

INT

> 1µs

Master samples

LINE TYPE LEGEND

Bus master pulling low

Resi stor pu l lup

GND

1-WIRE B US

15µs

VIH of Master

small

INT

small

Master samples

DS18B20

18 of 22

DS18B20 OPERATION EXAMPL E 1

In this example there are multiple DS18B20s on the bus and they are using parasite power. The bus

master initiates a temperature conversion in a specific DS18B20 and then reads its scratchpad and

recalculates t he CRC to ver ify the data.

MASTER MO DE

DATA (LSB FIRST )

COMMENTS

Reset

Master issues reset pulse.

Presence

DS18B20s respond wit h presence pulse.

55h

Master issues Match ROM command.

64-bit ROM code

Master sends DS18B20 ROM code.

44h

Master issues C onver t T command.

DQ line held high by

strong pullup

Master applies str ong pullup to DQ for t he dura tion of the

conver si on (tCONV).

Reset

Master issues reset pulse.

Presence

DS18B20s respond with pres ence pulse.

55h

Master issues Match ROM command.

64-bit ROM code

Master sends DS18B20 ROM code.

BEh

Master issues Read Scra tchpad c omman d.

Rx 9 data bytes

M as ter reads entire sc ratchp ad inc l udin g CR C. The mas ter

then recalcula tes the CRC of the f irst eight data bytes from t he

s c rat c hpad a nd c omp ares th e calc ulat e d CRC wi th t he read

CRC (byte 9). If they match, the master continues; if not, the

read o peration is repeated.

DS18B20 OPERATION EXAMPL E 2

In t his examp le there is o nl y o ne DS18B20 o n t he bus and it is u s ing par asite po wer. The mast er writ es to

the TH, TL, and configuration registers in the DS18B20 scratchpad and then reads the scratchpad and

recalculates t he CRC to ver ify the data. The master t hen co pies t he scratchpad contents to EEPROM.

MASTER MO DE

DATA (LSB FIRST )

COMMENTS

Reset

Master issues reset pulse.

Presence

DS18B20 responds with pres ence pulse.

CCh

Master issues Skip ROM command.

4Eh

Master issues Write Scra tchpad command.

3 data bytes

M as ter sends t hre e data byt es to s c ratchp ad ( T

, T

, and config).

Reset

Master issues reset pulse.

Presence

DS18B20 responds with pres ence pulse.

CCh

Master issues Skip ROM command.

BEh

Master issues Read Scratchpad c ommand.

Rx 9 data bytes

M as ter reads entire sc ratchp ad inc l udin g CR C. The mas ter th e n

recalculates the C RC of the first eight data bytes from the

s c rat c hpad a nd c omp ares the calculated CRC with the r ea d CRC

(byt e 9). If they match, the master continues; if not, the read

operation i s repeated.

Reset

Master issues reset pulse.

Presence

DS18B20 responds with pres ence pulse.

CCh

Master issues Skip ROM command.

48h

M as ter i ssues Cop y Scratchp ad c ommand.

DQ line held high by

strong pullup

Master applies str ong pullup to DQ for a t least 10ms while copy

oper atio n is i n progres s.

DS18B20

19 of 22

ABSOLUTE MAXIMUM RATINGS

Voltage Range on Any Pin R ela tive to Ground .................................................................. -0.5V to +6.0V

Operating Temp er ature Range ....................................................................................... -55°C to +125°C

Stor ag e T emperat ur e Range ........................................................................................... -55°C to +125°C

Solder T emperatu r e ..................................................... Refer to th e IP C/ JE D EC 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 aff ect reliability.

DC ELECTRICAL CHARACTERISTICS (-55°C to +125°C; VDD=3.0V to 5.5V)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

NOTES

Supp ly Voltage

VDD

Local P ower

+3.0

+5.5

Pu llup Supp ly

Voltage VPU

Parasite Power

+3.0

+5.5

V 1,2

Local P ower

+3.0

VDD

Thermometer

Error tERR

-10°C to +85°C

±0.5

°C 3

-55°C to +125°C

±2

Input Logic-Low

VIL

-0.3

+0.8

1,4,5

Input Logic-High VIH Local Power +2.2

The lower of

5.5

VDD + 0.3

V 1, 6

Parasite Power +3.0

Sink Curr ent

VI/O = 0.4V

4.0

St andby Current

IDDS

750

1000

7,8

Active Cu rrent

IDD

VDD = 5V

1.5

DQ Input Current

µA

Drift

±0.2

°C

NOTES:

1) All vo ltages ar e r eferenced to ground.

2) The Pullu p S up ply V oltage spec i fication assumes that the pu llup de vice is ideal, a nd t herefore the

high le vel of the pu llup is equal to VPU. In orde r to m eet the VIH spec o f the DS18B20 , t he act ual

supply ra il for t he stro ng pullup t r ansisto r must include margin for the volt age drop across t he

transistor when it is tur ned on; thus: VPU_ACTUAL = VPU_IDEAL + VTRANSISTOR.

3) See typical performance cu r ve in Figure 17.

4) Logic-lo w volt ages ar e specified at a sink current o f 4mA.

5) To gu ar ant ee a presence pulse under low voltage parasite power conditions, V ILMAX ma y have to be

reduced to as low as 0.5V.

6) Logic-high volt ag es are specified at a sour ce curr ent o f 1mA.

7) Standby cur rent specified up to +70°C. Standby curr ent typicall y is 3µA at +125°C.

8) To minimiz e I DDS, DQ s hould be within the follo wing ra nges: GND ≤ DQ ≤ GND + 0.3V or

VDD – 0.3V ≤ DQ ≤ VDD.

9) Active cu r r ent r efers to supply curr ent dur ing active temperat ur e co nversions o r EEP ROM writes.

10) DQ line is high (“high-Z” state).

11) Dr ift data is based o n a 1000-hour stress t est at +125°C with VDD = 5.5V.

DS18B20

20 of 22

AC ELECTRICAL CHARACTERISTICS—NV MEMORY

(-55°C to +100°C; VDD = 3.0V to 5.5V)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

NV Write Cycle Time

tWR

EEPROM Writes

NEEWR

-55°C to +55°C

50k

writes

EE P ROM Data Retentio n

tEEDR

-55°C to +55°C

years

AC ELECTRICAL CHARACTERISTICS (-55°C to +125°C; VDD = 3.0V to 5. 5V )

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

NOTES

Temper ature Conversio n

Time tCONV

9-bit resolution

93.75

ms 1

10-bit resolution

187.5

11-bit resolution

375

12-bit resolution

750

T ime to Str ong Pullup On tSPON

S tart Conve rt T

Command Issued

10 µs

T ime Slot t

SLOT

60 120 µ

Reco ver y Time

tREC

µs

Writ e 0 Low T ime

LOW0

120

µs

Writ e 1 Low T ime

LOW1

Read Dat a V alid

RDV

Re s e t Time High

RSTH

480

Reset Time Low

tRSTL

480

µs

1,2

Presence-Detect High

tPDHIGH

µs

Presence-Detect Low

PDLOW

240

µs

Capacitance

CIN/OUT

NOTES:

1) See the tim ing diag rams in Figure 18.

2) Under par as ite power, if tRSTL > 960µs, a power-on reset ma y o ccur .

Figure 17. Typical Performance Curve

DS18B20 Typical Error Curve

-0.5

-0.4

-0.3

-0.2

-0.1

0.1

0.2

0.3

0.4

0.5

010 20 30 40 50 60 70

Temperature (°C)

Thermomete r Error (°C)

Mean Error

+3s Error

-3s Error

DS18B20

21 of 22

Figure 18. Timing Diagrams

DS18B20

REVISION HISTORY

REVISION

DATE

DESCRIPTION

PAGES

CHANGED

030107

I n the Abs olute Maximum Ratings section, removed the reflo w oven

t emperat ur e va lue of +220°C. Reference t o JE DEC spec ificatio n for r eflo w

remains. 19

101207

I n the Operation—Alarm Signaling sect io n, added “or equa l t o” in the

des ci ption f or a TH alarm condition 5

I n the Memory section, re mo ved incor rect t ext d escribing me mo r y. 7

I n the Configuration Register sectio n, r emoved i ncorrect tex t describi ng

co nfiguration reg ister. 8

042208

In the Ordering Inf ormation table, added TO-92 st raig ht-lead packag es and

included a note that the TO-92 package in t ap e and reel ca n be o r d er ed with

either for med o r straight lead s.

Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.

Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical

Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.