MAX31820PARMCR+ - Maxim Integrated

General Description

The MAX31820PAR ambient temperature sensor pro-

vides 9-bit to 12-bit Celsius temperature measurements

with ±0.5°C accuracy over a +10°C to +45°C temperature

range. Over its entire -55°C to +125°C operating range,

the device has ±2.0°C accuracy.

The device communicates over a 1-Wire® bus that, by

definition, requires only one data line (and ground) for

communication with a central microprocessor. In addi-

tion, the device derives power directly from the data line

(“parasite power”), eliminating the need for an external

power supply. Requiring so few pins enables the device

to be placed in a 3-pin TO-92 package. The form factor

of this package allows the device to be placed above

the board and thus measure the ambient temperature of

a system, as opposed to the board temperature that a

surface-mount package would measure.

Each MAX31820PAR has a unique 64-bit serial code, which

allows multiple MAX31820PAR devices to function on the

same 1-Wire bus. Therefore, it is simple to use one micropro-

cessor to control many devices distributed over a large area.

Applications

● HVACEnvironmentalControls

● TemperatureMonitoringSystemsInsideBuildings,

Equipment, or Machinery

● ProcessMonitoringandControlSystems

● ThermostaticControls

● IndustrialSystems

● ConsumerProducts

● Thermometers

● AnyThermallySensitiveSystem

Benets and Features

● Unique1-WireInterfaceRequiresOnlyOnePortPin

for Communication

● DerivesPowerfromDataLine(ParasitePower);No

LocalPowerSupplyNeeded

● MultidropCapabilitySimplifiesDistributed

Temperature-SensingApplications

● RequiresNoExternalComponents

● MeasuresTemperaturesfrom-55°Cto+125°C(-67°F

to+257°F)

● ±0.5°CAccuracyfrom+10°Cto+45°C

● ThermometerResolutionisUser-Selectablefrom

9Bits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3-PinTO-92Package

● SoftwareCompatiblewiththeDS1822-PARand

DS18B20-PAR

Ordering Information appears at end of data sheet.

For related parts and recommended products to use with this part, refer

to www.maximintegrated.com/MAX31820PAR.related.

1-Wire is a registered trademark of Maxim Integrated Products, Inc.

MAX31820PAR

64-BIT ROM

AND

1-Wire PORT

PARASITE-POWER

CIRCUIT

CPP

VPU

4.7kΩ

GND

MEMORY

CONTROL LOGIC

SCRATCHPAD

8-BIT CRC GENERATOR

CONFIGURATION REGISTER (EEPROM)

TEMPERATURE REGISTER

ALARM HIGH TRIGGER (TH)

ALARM LOW TRIGGER (TL)

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

19-6732; Rev 0; 6/13

Block Diagram

VoltageRangeonAnyPinRelativetoGround ....-0.5Vto+6.0V

Operating Temperature Range ......................... -55°C to +100°C

StorageTemperatureRange ............................ -55°C to +125°C

SolderingTemperature(reflow) ....................................... +260°C

(VPU=3.0Vto3.7V,TA=-55°Cto+100°C,unlessotherwisenoted.)(Note1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

PullupSupplyVoltage VPU (Notes2,3) 3.0 3.7 V

Thermometer Error TERR

+10°C to +45°C ±0.5 °C

-55°C to +100°C ±2

InputLogic-Low VIL (Notes2,4,5) -0.3 +0.8 V

InputLogic-High VIH (Notes2,6) 3.0 3.7 V

SinkCurrent ILVI/O=0.4V(Note2) 4.0 mA

Active Current IDQA (Note7) 1 1.5 mA

DQInputCurrent IDQ (Note8) 5 µA

Drift (Note9) ±0.2 °C

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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Absolute Maximum Ratings

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these

or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect

device reliability.

DC Electrical Characteristics

(VPU=3.0Vto3.7V,TA=-55°Cto+100°C,unlessotherwisenoted.)(Note1)

Note 1: Limitsare100%testedatTA = +25°C and TA=+85°C.Limitsovertheoperatingtemperaturerangeandrelevantsupply

voltage are guaranteed by design and characterization.

Note 2: All voltages are referenced to ground.

Note 3: The pullup supply voltage specification assumes that the pullup device (resistor or transistor) is ideal, and therefore the

highlevelofthepullupisequaltoVPU.Inordertomeetthedevice’sVIH spec, the actual supply rail for the strong pullup

transistormustincludemarginforthevoltagedropacrossthetransistorwhenitisturnedon;thus:VPU_ACTUAL=VPU_

IDEAL+VTRANSISTOR.

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,VILMAX 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: Active current refers to supply current during active temperature conversions or EEPROM writes.

Note 8: DQlineishigh(high-Zstate).

Note 9: Driftdataisbasedona1000-hourstresstestat+125°C.

Note 10: Seethe1-Wire Timing Diagrams.

Note 11: If tRSTL > 960µs, a power-on reset may occur.

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Temperature Conversion Time tCONV

9-bit resolution 93.75

10-bit resolution 187.5

11-bit resolution 375

12-bit resolution 750

TimetoStrongPullupOn tSPON StartConvertTcommandorCopy

Scratchpadcommandissued 10 µs

TimeSlot tSLOT (Note10) 60 120 µs

Recovery Time tREC (Note10) 1 µs

Write-ZeroLowTime tLOW0 (Note10) 60 120 µs

Write-OneLowTime tLOW1 (Note10) 1 15 µs

ReadDataValid tRDV (Note10) 15 µs

ResetTimeHigh tRSTH (Note10) 480 µs

ResetTimeLow tRSTL (Notes10,11) 480 960 µs

Presence-DetectHigh tPDHIGH (Note10) 15 60 µs

Presence-DetectLow tPDLOW (Note10) 60 240 µs

Capacitance CIN/OUT 25 pF

NONVOLATILE MEMORY

NonvolatileWriteCycleTime tWR 2 10 ms

EEPROM Writes NEEWR -55°C to +55°C 50k Writes

EEPROMDataRetention tEEDR -55°C to +55°C 10 Years

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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AC Electrical Characteristics

1-Wire WRITE-ZERO TIME SLOT

1-Wire READ-ZERO TIME SLOT

1-Wire RESET PULSE

1-Wire PRESENCE DETECT

RESET PULSE FROM HOST

PRESENCE DETECT

tSLOT

tRSTL tRSTH

START OF NEXT CYCLE

tLOW0

tREC

tPDHIGH

tPDLOW

tRDV

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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1-Wire Timing Diagrams

Detailed Description

The MAX31820PAR ambient temperature sensor

provides 9-bit to 12-bit Celsius temperature measure-

ments with ±0.5°C accuracy over a +10°C to +45°C tem-

perature range. Over its entire -55°C to +125°C operating

range, the device has ±2.0°C accuracy. The device com-

municates over a 1-Wire bus that, by definition, requires

only one data line (and ground) for communication with

a central microprocessor. In addition, the device derives

power directly from the data line (“parasite power”),

eliminating the need for an external power supply.

Requiring so few pins enables the device to be placed

in a 3-pin TO-92 package. The form factor of this pack-

age allows the device to be placed above the board and

thus measure the ambient temperature of a system, as

opposed to the board temperature that a surface-mount

package would measure.

Each device has a unique 64-bit serial code, allowing

multiple MAX31820PAR devices to function on the same

1-Wire bus. Therefore, it is simple to use one micro-

processor to control many devices distributed over a

large area. 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 pro-

vides access to the 1-byte upper and lower alarm trigger

registers (TH and TL) and the 1-byte configuration regis-

ter. The configuration register allows the user to set the

resolution of the temperature-to-digital conversion to 9,

10, 11, or 12 bits. The TH, TL, and configuration registers

are nonvolatile (EEPROM), so they retain data when the

device is powered down.

The device uses Maxim Integrated’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 through a

three-state or open-drain port (i.e., the MAX31820PAR’s

DQ pin). 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.

The device can also operate without an external power

supply. Power is instead supplied through the 1-Wire

pullupresistorthroughtheDQpinwhenthebusishigh.

The high bus signal also charges an internal capacitor

(CPP), 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.”

N.C.

GND

TO-92

FRONT VIEW

MAX31820PAR

SIDE VIEW

PIN NAME FUNCTION

1GND Ground

2DQ DataInput/Output.Open-drain,1-Wireinterfacepinthatprovidespowertothedevicewhenusedin

parasite power mode (see the Parasite Power section).

3N.C. NotConnected.Doesnotconnecttointernalcircuit.

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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Pin Description

Pin Conguration

*The power-on-reset value of the temperature register is +85°C.

Operation

Measuring Ambient Temperature

A conventional surface-mount temperature sensor IC

has an excellent thermal connection to the circuit board

on which it is mounted. Heat travels from the board

through the leads to the sensor die. Air temperature can

affect the die temperature, but the sensor’s package

does not conduct heat as well as the leads, so board

temperature has the greatest influence on the measured

temperature.

The device’s TO-92 package allows the sensor die to be

positioned above the board. The leads still conduct some

heat from the board, but because there is significant lead

area in contact with air, their temperature is also strongly

affectedbyairtemperature.Followtheguidelinesbelowto

getthebestresultswhenmeasuringambienttemperature:

• If air is moving (e.g., due to cooling fans), place the

sensor in the path of the air stream. This causes the

ambient temperature to influence the sensor tempera-

ture more strongly.

• If the board contains components that will heat it, mount

the sensor as far as possible from those components.

This makes the temperature in the vicinity of the sensor

closer to the temperature of the ambient air.

• PCB traces and ground planes conduct heat from

other components to the sensor. As much as practical,

avoid copper in the vicinity of the sensor.

The device’s core functionality is its direct-to-digital tem-

perature 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 bits.

The device 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 device returns to its idle state.

The 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 the Temperature

tureispositiveornegative:forpositivenumbersS=0and

fornegative numbers S= 1.If thedevice is configured

for 12-bit resolution, all bits in the temperature register

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 correspond-

ing temperature reading for 12-bit resolution conversions.

Temperature Register Format

Table 1. Temperature/Data Relationship

BIT 15 BIT 14 BIT 13 BIT 12 BIT 11 BIT 10 BIT 9 BIT 8

MSB SSSSS262524

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

LSB 232221202-1 2-2 2-3 2-4

TEMPERATURE (°C) DIGITAL OUTPUT (BINARY) DIGITAL OUTPUT (HEX)

+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

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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Alarm Signaling

After the device performs a temperature conversion, the

temperature value is compared to the user-defined two’s

complement alarm trigger values stored in the 1-byte TH

and TL registers (see TH and TL Register Format). The

signbit(S) indicatesifthevalueispositiveornegative;

forpositivenumbersS=0andfornegativenumbersS

= 1. The TH and TL registers are nonvolatile (EEPROM)

so they retain data when the device is powered down.

TH and TL can be accessed through bytes 2 and 3 of the

scratchpad, as explained in the Memory section.

Onlybits11:4ofthetemperatureregisterareusedinthe

TH and TL comparison since TH and TLare 8-bit registers.

If the measured temperature is lower than or equal to TL

or higher than or equal to TH, an alarm condition exists

and an alarm flag is set inside the device. This flag is

updatedaftereverytemperaturemeasurement;therefore,

if the alarm condition goes away, the flag is turned off after

the next temperature conversion.

The master device can check the alarm flag status of all

MAX31820PAR devices on the bus by issuing an Alarm

Search[ECh]command.Anydeviceswithasetalarmflag

respond to the command, so the master can determine

exactly which devices have experienced an alarm condi-

tion. If an alarm condition exists and the TH or TL settings

have changed, another temperature conversion should be

done to validate the alarm condition.

TH and TL Register Format

Parasite Power

The device’s parasite-power circuit allows it to operate

without a local power supply. Parasite power is very

useful for applications that require remote temperature

sensing, or those that are very space constrained.

Figure 1 shows the device’s parasite-power control

circuitry, which “steals” power from the 1-Wire bus

through the DQ pin when the bus is high. The stolen

charge powers the device while the bus is high, and

some of the charge is stored on the parasite-power

capacitor (CPP) to provide power when the bus is low.

In parasite-power mode, the 1-Wire bus and CPP can

provide sufficient current to the device for most opera-

tions as long as the specified timing and voltage require-

ments are met (see the DC Electrical Characteristics and

AC Electrical Characteristics tables).However,whenthe

device is performing temperature conversions or copy-

ing data from the scratchpad memory to EEPROM, the

operating current can be as high as 1.5mA. This current

can cause an unacceptable voltage drop across the weak

1-Wire pullup resistor and is more current than can be

supplied by CPP. To ensure that the device 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 scratch-

pad to EEPROM. This can be accomplished by using a

MOSFET to pull the bus directly to the rail, as shown

Figure 1. Supplying the Parasite-Powered MAX31820PAR During Temperature Conversions

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

S26252423222120

µP

VPU

4.7kΩ

VPU

1-Wire BUS TO OTHER 1-Wire DEVICES

MAX31820PAR

GND DQ

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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in Figure 1. The 1-Wire bus must be switched to the

strong pullup within 10µs (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 (tCONV) or data transfer (tWR = 10ms). No

other activity can take place on the 1-Wire bus while the

pullup is enabled.

64-Bit Lasered ROM Code

Each device contains a unique 64-bit code stored in

ROM (Figure2). The least significant 8 bits of the ROM

code contain the device’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 from the first 56 bits of the ROM

code. A detailed explanation of the CRC bits is provided

in the CRC Generation section. The 64-bit ROM code and

associated ROM function control logic allow the device to

operate as a 1-Wire device using the protocol detailed in

the 1-Wire Bus System section.

Memory

The device’s memory is organized as shown in

Figure3.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devicealarmfunctionisnotused,theTH

and TL registers can serve as general-purpose memory.

All memory commands are described in detail in the

MAX31820PAR 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containstheconfigurationregis-

ter data, which is explained in detail in the Configuration

thedeviceandcannotbeoverwritten.Byte8ofthescratch-

padisread-onlyandcontainstheCRCcodeforbytes7:0

of the scratchpad. The device generates this CRC using

the method described in the CRC Generation section.

Figure 2. 64-Bit Lasered ROM Code

Figure 3. Memory Map

MSb

8-BIT

CRC CODE 48-BIT SERIAL NUMBER

MSb MSbLSb

LSb

8-BIT FAMILY CODE

(28h)

MSbLSb

TEMPERATURE REGISTER LSB (50h)BYTE 0

TEMPERATURE REGISTER MSB (05h)BYTE 1

TH REGISTER OR USER BYTE 1*BYTE 2

TL REGISTER OR USER BYTE 2*BYTE 3

CONFIGURATION REGISTER*BYTE 4

RESERVED (FFh)BYTE 5

RESERVEDBYTE 6

RESERVED (10h)BYTE 7

CRC*BYTE 8

*POWER-UP STATE DEPENDS ON VALUE(S) STORED IN EEPROM.

SCRATCHPAD (POWER-UP STATE

SHOWN IN PARENTHESES)

EEPROM

TH REGISTER OR USER BYTE 1

TL REGISTER OR USER BYTE 2

CONFIGURATION REGISTER

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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Dataiswrittentobytes4:2 of thescratchpadusingthe

Write Scratchpad [4Eh] command; the data must be

transmitted to the device 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 transfer the TH, TL, and

configuration data from the scratchpad to EEPROM, the

mastermustissuetheCopyScratchpad[48h]command.

Data in the EEPROM registers is retained when the

deviceispowereddown;atpower-uptheEEPROMdata

is reloaded into the corresponding scratchpad locations.

DatacanalsobereloadedfromEEPROMtothescratch-

pad at any time using the Recall E2[B8h]command.The

master can issue read time slots following the Recall

E2 command, and the device indicates the status of the

recall by transmitting 0 while the recall is in progress and

1 when the recall is done.

Conguration Register

Byte4ofthescratchpadmemorycontainstheconfigura-

tion register, which is organized as shown in Configuration

tion of the device using the R0 and R1 bits in this register,

as shown in Table 2. The power-up default of these bits is

R0=1andR1=1(12-bitresolution).Notethatthereis

a direct trade-off between resolution and conversion time.

Bit7andbits4:0intheconfigurationregisterarereserved

for internal use by the device and cannot be overwritten.

Conguration Register Format

Table 2. Thermometer Resolution Configuration

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

0 R1 R0 1 1 1 1 1

R1 R0 RESOLUTION (BITS) MAX CONVERSION 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)

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

CRC Generation

CRC bytes are provided as part of the device’s 64-bit

ROM code and in the 9th byte of the scratchpad memory.

The ROM code CRC is calculated from the first 56 bits

of the ROM code and is contained in the most significant

byte of the ROM. The scratchpad CRC is calculated from

the data stored in the scratchpad, and therefore changes

when the data in the scratchpad changes. The CRCs

provide the bus master with a method of data validation

when data is read from the device. To verify that data has

been read correctly, the bus master must recalculate the

CRC from the received data and then compare this value

to either the ROM code CRC (for ROM reads) or to the

scratchpad CRC (for scratchpad 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 device that prevents a command sequence from pro-

ceeding if the device CRC (ROM or scratchpad) does not

match the value generated by the bus master.

The equivalent polynomial function of the CRC (ROM or

scratchpad)is:

CRC = X8 + X5 + X4 + 1

The bus master can recalculate the CRC and compare

it to the CRC values from the MAX31820PAR using the

polynomial generator shown in Figure 4. This circuit

consists of a shift register and XOR gates, and the shift

significant bit of the ROM code or the least significant bit

of byte 0 in the scratchpad, one bit at a time should be

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 polynomial generator contains the

recalculatedCRC.Next,the8-bitROMcodeorscratch-

pad CRC from the device must be shifted into the circuit.

At this point, if the recalculated CRC was correct, the shift

Maxim Integrated 1-Wire CRC is available in Application

Note 27: Understanding and Using Cyclic Redundancy

Checks with Maxim iButton® Products.

iButton is a registered trademark of Maxim Integrated

Products, Inc.

Figure 4. CRC Generator

1ST

STAGE

2ND

STAGE

3RD

STAGE

4TH

STAGE

7TH

STAGE

8TH

STAGE

6TH

STAGE

5TH

STAGE

X0X1X2X3X4

POLYNOMIAL = X8 + X5 + X4 + 1

INPUT DATA

X5X6X7X8

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

1-Wire Bus System

The 1-Wire bus system uses a single bus master to con-

trol one or more slave devices. The MAX31820PAR is

always a slave. When there is only one slave on the bus,

thesystemisreferredtoasasingle-dropsystem;thesys-

tem is multidrop if there are multiple slaves on the bus. All

data and commands are transmitted least significant bit

first over the 1-Wire bus.

The following discussion of the 1-Wire bus system is

broken down into three topics: hardware configuration,

transaction sequence, and 1-Wire signaling (signal types

and timing).

Hardware Conguration

The 1-Wire bus has, by definition, only a single data line.

Each device (master or slave) interfaces to the data line

through an open-drain or three-state port. This allows

each device to release the data line when the device is

not transmitting data so the bus is available for use by

another device. The 1-Wire port of the MAX31820PAR

(theDQpin)isopendrainwithaninternalcircuitequiva-

lent to that shown in Figure5.

The 1-Wire bus requires an external pullup resis-

tor of approximately 5kΩ; thus, the idle state for the

1-Wire bus is high. If for any reason a transaction needs

to be suspended, the bus must be left in the 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

inactive (high) state during the recovery period. If the bus

is held low for more than 480µs, all components on the

bus will be reset. Additionally, to ensure that the device

has sufficient supply current during temperature conver-

sions, it is necessary to provide a strong pullup (such as

a MOSFET) on the 1-Wire bus whenever temperature

conversions or EEPROM writes are taking place (as

described in the Parasite Power section.

Transaction Sequence

The transaction sequence for accessing the device is as

follows:

1) Step1:Initialization

2) Step2:ROMcommand(followedbyanyrequireddata

exchange)

3) Step3:MAX31820PARFunctioncommand(followed

by any required data exchange)

It is very important to follow this sequence every time

the device is accessed, as the device does not 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mastermustreturntoStep1

in the sequence.

Initialization

All transactions on the 1-Wire bus begin with an initializa-

tion sequence. The initialization sequence consists of a

reset pulse transmitted by the bus master, followed by

presence pulse(s) transmitted by the slave(s). The pres-

ence pulse lets the bus master know that slave devices

(such as the MAX31820PAR) are on the bus and are

ready to operate. Timing for the reset and presence

pulses is detailed in the 1-Wire Signaling section.

Figure 5. Hardware Configuration

4.7kΩ

5µA

TYP

VPU

MICROPROCESSOR

100Ω

MOSFET

1-Wire BUS

STRONG

PULLUP

MAX31820PAR 1-Wire PORT

RX = RECEIVE

TX = TRANSMIT

VPU

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

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 of each slave device

and allow the master to single out a specific device if

many are present on the 1-Wire bus. These commands

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 MAX31820PAR Function command. Figure 6

shows a flowchart for operation of the ROM commands.

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 the ROM

codes through a process of elimination that requires the

mastertoperformaSearchROMcycle(i.e.,SearchROM

command followed by data exchange) as many times as

necessary to identify all the slave devices. If there is only

one slave on the bus, the simpler Read ROM command

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

detailedexplanationoftheSearchROMprocedure,refer

to ApplicationNote937:Book of iButton Standards. After

everySearchROMcycle,thebusmastermustreturnto

Step1(initialization)inthetransactionsequence.

Read ROM [33h]

This command can only be used when there is one slave

on the bus. It allows the bus master to read the slave’s

64-bitROMcodewithoutusingtheSearchROMproce-

dure. If this command is used when there is more than

one slave present on the bus, a data collision occurs

when all the slaves attempt to respond at the same time.

Match ROM [55h]

The match ROM command, followed by a 64-bit ROM

code sequence, allows the bus master 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 responds to the function command issued by

themaster; allother slaveson thebus waitfor areset

pulse.

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

devices on the bus perform simultaneous temperature

conversionsby issuinga SkipROM command followed

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 from the slave without send-

ingthedevice’s64-bitROMcode.ASkipROMcommand

followedbyaReadScratchpadcommandcausesadata

collision on the bus if there is more than one slave since

multiple devices attempt to transmit data simultaneously.

Alarm Search [ECh]

The operation of this command is identical to the opera-

tionoftheSearchROMcommandexceptthatonlyslaves

with a set alarm flag respond. This command allows

the master device to determine if any MAX31820PARs

experienced an alarm condition during the most recent

temperatureconversion.AftereveryAlarmSearchcycle

(i.e.,AlarmSearchcommandfollowedbydataexchange),

thebusmastermustreturntoStep1(initialization)inthe

transaction sequence. See the Alarm Signaling section

for an explanation of alarm flag operation.

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Figure 6. ROM Commands Flowchart

F0h

ROM?

BIT 0

MATCH?

BIT 0

MATCH?

CCh

SKIP

ROM?

55h

MATCH

ROM?

33h

READ

ROM?

YY Y

MASTER TX

BIT 0

DEVICE TX

FAMILY CODE

1 BYTE

MASTER TX

FUNCTION COMMAND

DEVICE TX

SERIAL NUMBER

6 BYTES

DEVICE TX

CRC BYTE

MASTER TX

ROM COMMAND

DEVICE TX

PRESENCE PULSE

MASTER TX

RESET PULSE

INITIALIZATION

SEQUENCE

DEVICE TX BIT 0

MASTER TX BIT 0

MASTER TX

BIT 63

DEVICE TX BIT 63

MASTER TX BIT 63

BIT 1

MATCH?

BIT 1

MATCH?

BIT 63

MATCH?

BIT 63

MATCH?

ECh

ALARM SEARCH

COMMAND

DEVICE(S)

WITH ALARM

FLAG SET?

DEVICE TX BIT

MASTER TX BIT 0

Y Y

MASTER TX

BIT 1

DEVICE TX BIT 1

MASTER TX BIT 1

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Note 1: The master must enable a strong pullup on the 1-Wire bus during temperature conversions and copies from the scratchpad

toEEPROM.Nootherbusactivitycan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 3 bytes must be written before a reset is issued.

MAX31820PAR Function Commands

After the bus master has used a ROM command to

address the device with which it wishes to communi-

cate, the master can issue one of the device function

commands. These commands allow the master to write

to and read from the device’s scratchpad memory,

initiate temperature conversions, and determine the

power-supply mode. Table 3 summarizes the device

function commands, and Figure7 illustrates the function

commands.

Convert T [44h]

This command initiates a single temperature conversion.

Following the conversion, the resulting thermal data is

stored in the 2-byte temperature register in the scratch-

pad memory and the device returns to its low-power idle

state. 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 conversion (tCONV), as described in

the Parasite Power section.

Write Scratchpad [4Eh]

This command allows the master to write 3 bytes of data

to the device’s scratchpad. The first data byte 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 command allows the master to read the contents

of the scratchpad. The data transfer starts with the least

significant bit of byte 0 and continues through the scratch-

pad until the 9th byte (byte 8 – CRC) is read. The master

can issue a reset to terminate reading at any time if only

part of the scratchpad data is needed.

Copy Scratchpad [48h]

This command copies the contents of the scratchpad

TH, TL and configuration registers (bytes 2, 3, and 4)

to EEPROM. 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 Parasite

Power 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, respectively, in the scratchpad

memory. The master device can issue read time slots fol-

lowing the Recall E2 command and the device indicates

the status of the recall by transmitting 0 while the recall

is in progress and 1 when the recall is done. The recall

operation happens automatically at power-up, so valid

data is available in the scratchpad as soon as power is

applied to the device.

Table 3. MAX31820PAR Function Command Set

COMMAND DESCRIPTION PROTOCOL 1-Wire BUS ACTIVITY AFTER COMMAND IS

ISSUED

Convert T

(Note1) Initiates temperature conversion. 44h None.

ReadScratchpad

(Note2)

Reads the entire scratchpad

including the CRC byte. BEh The device transmits up to 9 data bytes to master.

WriteScratchpad

(Note3)

Writes to scratchpad bytes 2, 3,

and 4 (TH, TL,andconguration

registers).

4Eh The master transmits 3 data bytes to the device.

CopyScratchpad

(Note1)

Copies TH, TL,andconguration

EEPROM.

48h None.

Recall E2

Recalls TH, TL,andconguration

scratchpad.

B8h The device transmits recall status to the master.

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Figure 7. MAX31820PAR Function Commands Flowchart

44h

CONVERT

Y Y

MASTER TX

FUNCTION COMMAND

MASTER ENABLES

STRONG PULLUP ON DQ

DEVICE CONVERTS

TEMPERATURE

MASTER DISABLES

STRONG PULLUP

MASTER ENABLES

STRONG PULLUP ON DQ

DATA COPIED FROM

SCRATCHPAD TO EEPROM

MASTER DISABLES

STRONG PULLUP

48h

COPY

SCRATCHPAD?

MASTER TX TH BYTE

TO SCRATCHPAD

4Eh

WRITE

SCRATCHPAD

MASTER TX TL BYTE

TO SCRATCHPAD

MASTER TX CONFIG.

BYTE TO SCRATCHPAD

BEh

READ

SCRATCHPAD

MASTER RX DATA BYTE

FROM SCRATCHPAD

MASTER BEGINS DATA

RECALL FROM E2 PROM

RETURN TO INITIALIZATION SEQUENCE

FOR NEXT TRANSACTION

MASTER RX SCRATCHPAD

CRC BYTE

MASTER TX

RESET?

HAVE 8 BYTES

BEEN READ?

B8h

RECALL E2

MASTER RX

“1s”

MASTER RX

“0s”

DEVICE

BUSY RECALLING

DATA

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

1-Wire Signaling

The MAX31820PAR uses a strict 1-Wire communication

protocoltoensuredataintegrity.Severalsignaltypesare

definedbythisprotocol:resetpulse,presencepulse,write

0, write 1, read 0, and read 1. The bus master initiates all

these signals, with the exception of the presence pulse.

Initialization Procedure: Reset and Presence

Pulses

All communication with the device begins with an initial-

ization sequence that consists of a reset pulse from the

master followed by a presence pulse from the device,

as illustrated in Figure 8. When the device sends the

presence pulse in response to the reset, it is indicating to

the master that it is on the bus and ready to operate.

During the initialization sequence, the bus master

transmits (TX) the reset pulse by pulling the 1-Wire bus

low for a minimum of 480µs. The bus master then releas-

es the bus and goes into receive mode (RX). When the

busisreleased,the5kΩpullupresistorpullsthe1-Wire

bus high. When the device detects this rising edge, it

waits 15µs to 60µs and then transmits a presence pulse

by pulling the 1-Wire bus low for 60µs to 240µs.

Figure 8. Initialization Timing

VPU

1-Wire BUS

MASTER TX RESET PULSE

480µs MINIMUM

MASTER RX

480µs MINIMUM

DEVICE TX PRESENCE PULSE

60µs TO 240µs

DEVICE WAITS

15µs TO 60µs

GND

BUS MASTER PULLING LOW DEVICE PULLING LOW RESISTOR PULLUP

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Ambient Temperature Sensor

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│

Read/Write Time Slots

The bus master writes data to the device during write time

slots and reads data from the device during read time

slots. One bit of data is transmitted over the 1-Wire bus

per time slot.

Write Time Slots

There are two types of write time slots: write-one time

slots and write-zero time slots. The bus master uses a

write-one time slot to write a logic 1 to the device and a

write-zero time slot to write a logic 0 to the device. All write

time slots must be a minimum of 60µs in duration with a

minimum of a 1µs recovery time between individual write

slots. Both types of write time slots are initiated by the

master pulling the 1-Wire bus low (Figure9).

To generate a write-one time slot, after pulling the 1-Wire

bus low, the bus master must release the 1-Wire bus

within 15µs. When the bus is released, the 5kΩ pullup

resistor pulls the bus high. To generate a write-zero time

slot, after pulling the 1-Wire bus low, the bus master must

continue to hold the bus low for the duration of the time

slot (at least 60µs).

The device samples the 1-Wire bus during a window that lasts

from 15µs to 60µs after the master initiates the write time slot.

If the bus is high during the sampling window, a 1 is written to

the device. If the line is low, a 0 is written to the device.

Figure 9. Read/Write Time Slot Timing Diagram

VPU

1-Wire BUS

START

OF SLOT

START

OF SLOT

60µs < TX “0” < 120µs

1µs < tREC < ∞

> 1µs

MASTER SAMPLES MASTER SAMPLES

> 1µs

15µs 15µs 30µs

MASTER WRITE-ZERO SLOT

DEVICE SAMPLES

MIN MAXTYP

DEVICE SAMPLES

MIN MAXTYP

MASTER WRITE-ONE SLOT

MASTER READ-ZERO SLOT MASTER READ-ONE SLOT

GND

VPU

1-Wire BUS

GND

15µs 45µs 15µs

15µs 15µs 30µs

BUS MASTER PULLING LOW DEVICE PULLING LOW RESISTOR PULLUP

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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│

Read Time Slots

The device can only transmit data to the master when

the master issues read time slots. Therefore, the master

must generate read time slots immediately after issuing

a Read Scratchpad [BEh] command, so that the device

can provide the requested data. In addition, the master

can generate read time slots after issuing a Recall E2

[B8h]commandtofindoutthestatusoftheoperation,as

explained in the Parasite Power 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 minimum of 1µs and then releasing

the bus (Figure9). After the master initiates the read time

slot, the device begins transmitting a 1 or 0 on the bus.

The device transmits a 1 by leaving the bus high and

transmits a 0 by pulling the bus low. When transmitting

a 0, the device releases the bus by the end of the time

slot, and the bus is pulled back to its high idle state by

the pullup resister. Output data from the device is valid

for 15µs after the falling edge that initiated the read time

slot. Therefore, the master must release the bus and then

sample the bus state within 15µs from the start of the slot.

Figure 10 illustrates that the sum of tINIT, tRC, and

tSAMPLE must be less than 15µs for a read time slot.

Figure11 shows that system timing margin is maximized

by keeping tINIT and tRC as short as possible and by

locating the master sample time during read time slots

towards the end of the 15µs period.

Figure 10. Detailed Master Read-One Timing

Figure 11. Recommended Master Read-One Timing

VIH OF MASTER

MASTER SAMPLES

VPU

1-Wire BUS

GND

15µs

tINIT > 1µs tRC

BUS MASTER PULLING LOW RESISTOR PULLUP

VPU

VIH OF MASTER

tINIT =

SMALL

tRC =

SMALL

MASTER SAMPLES

15µs

1-Wire BUS

GND

BUS MASTER PULLING LOW RESISTOR PULLUP

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

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│

Operation Examples

Example 1

In Table 4 there are multiple devices on the bus. The bus

master initiates a temperature conversion in a specific

MAX31820PAR and then reads its scratchpad and recal-

culates the CRC to verify the data.

Example 2

In Table 5 there is only one device on the bus. The

master writes to the TH, TL, and configuration registers

in the device’s scratchpad and then reads the scratchpad

and recalculates the CRC to verify the data. The master

then copies the scratchpad contents to EEPROM.

Table 4. Operation Example 1

Table 5. Operation Example 2

MASTER

MODE

DATA

(LSB FIRST) COMMENTS

Tx Reset Master issues reset pulse.

Rx Presence Devicesrespondwithpresencepulse.

Tx 55h Master issues Match ROM command.

Tx 64-bit ROM code Master sends device ROM code.

Tx 44h Master issues Convert T command.

Tx DQlineheldhighby

strong pullup MasterappliesstrongpulluptoDQforthedurationoftheconversion(tCONV).

Tx Reset Master issues reset pulse.

Rx Presence Devicesrespondwithpresencepulse.

Tx 55h Master issues Match ROM command.

Tx 64-bit ROM code Master sends device ROM code.

Tx BEh MasterissuesReadScratchpadcommand.

Rx 9 data bytes

Master reads entire scratchpad including CRC. The master then recalculates the CRC of the

rst8databytesfromthescratchpadandcomparesthecalculatedCRCwiththereadCRC

(byte9).Iftheymatch,themastercontinues;ifnot,thereadoperationisrepeated.

MASTER

MODE

DATA

(LSB FIRST) COMMENTS

Tx Reset Master issues reset pulse.

Rx Presence Devicerespondswithpresencepulse.

Tx CCh MasterissuesSkipROMcommand.

Tx 4Eh MasterissuesWriteScratchpadcommand.

Tx 3 data bytes Master sends 3 data bytes to the scratchpad (TH, TL,andcongurationregisters).

Tx Reset Master issues reset pulse.

Rx Presence Devicerespondswithpresencepulse.

Tx CCh MasterissuesSkipROMcommand.

Tx BEh MasterissuesReadScratchpadcommand.

Rx 9 data bytes

Master reads entire scratchpad including CRC. The master then recalculates the CRC of the

rst8databytesfromthescratchpadandcomparesthecalculatedCRCwiththereadCRC

(byte9).Iftheymatch,themastercontinues;ifnot,thereadoperationisrepeated.

Tx Reset Master issues reset pulse.

Rx Presence Devicerespondswithpresencepulse.

Tx CCh MasterissuesSkipROMcommand.

Tx 48h MasterissuesCopyScratchpadcommand.

Tx DQlineheldhighby

strong pullup MasterappliesstrongpulluptoDQforatleast10mswhilecopyoperationisinprogress.

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

+Denotes a lead(Pb)-free/RoHS-compliant package.

T = Tape and reel.

PART TEMP RANGE PIN-PACKAGE

MAX31820PARMCR+ -55°C to +125°C 3 TO-92 (straight leads)

MAX31820PARMCR+T -55°C to +125°C 3 TO-92 (formed leads)

PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.

3 TO-92 (straight leads) Q3+1 21-0248 —

3 TO-92 (formed leads) Q3+4 21-0250 —

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

www.maximintegrated.com Maxim Integrated

│

Package Information

Forthelatestpackageoutlineinformationandlandpatterns(footprints),goto www.maximintegrated.com/packages.Notethata“+”,

“#”,or“-”inthepackagecodeindicatesRoHSstatusonly.Packagedrawingsmayshowadifferentsuffixcharacter,butthedrawing

pertainstothepackageregardlessofRoHSstatus.

Ordering Information

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES

CHANGED

0 6/13 Initial release —

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

are implied. Maxim Integrated reserves the right to change the circuitry and specications 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.

Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.

MAX31820PAR 1-Wire, Parasite-Power,

Ambient Temperature Sensor

│

Revision History

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

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MAX31820PARMCR+T MAX31820PARMCR+