MAXIM MAX31826 Technical data

19-6264; Rev 0; 3/12

MAX31826

1-Wire Digital Temperature Sensor

with 1Kb Lockable EEPROM

General Description

The MAX31826 digital thermometer provides 12-bit temperature measurements and communicates over a

M

1-Wire

bus that by definition requires only one data line (and ground) for communication with a central microcontroller. It has a -55NC to +125NC operating temperature range and is accurate to Q0.5NC over the -10NC to +85NC range. In addition, the device can derive power directly from the data line (“parasite power”), eliminating the need for an external power supply.

Each device has a unique 64-bit serial code, which allows multiple devices to function on the same 1-Wire bus. Therefore, it is simple to use one microcontroller (the master device) to control many devices distributed over a large area. The device includes 128 bytes (1Kb) of EEPROM for storage of system data. The EEPROM can be locked to permanently prevent any further data writes. Four location address inputs simplify mapping of individual devices to specific locations.

Applications

Industrial Systems

Building Automation

Consumer Equipment

System Calibration

Module Identification

Benefits and Features

S Unique 1-Wire Interface Requires Only One Port

Pin for Communication

S Integrated Temperature Sensor and EEPROM

Reduce Component Count

Measures Temperatures from -55NC to +125NC



(-67NF to +257NF)

±0.5NC Accuracy from -10NC to +85NC



12-Bit Temperature Resolution (0.0625NC)



1Kb EEPROM Can Be Locked to Prevent Further



Writes

S Multidrop Capability Simplifies Multisensor

Systems

Each Device Has a Unique 64-Bit Serial Code



Stored in On-Board ROM

Four Pin-Programmable Bits to Uniquely



Identify Up to 16 Sensor Locations on a Bus

S Can Be Powered from Data Line (3.0V to 3.7V

Power-Supply Range)

S 8-Pin µMAX® Package

Ordering Information appears at end of data sheet.

For related parts and recommended products to use with this part, refer to www.maxim-ic.com/MAX31826.related.

Block Diagram

V

PU

4.7kΩ

MEMORY

DQ

GND

V

DD

1-Wire and µMAX are registered trademarks of Maxim Integrated Products, Inc.

�� Maxim Integrated Products 1

PARASITE-

POWER

CIRCUIT

POWERSUPPLY

SENSE

64-BIT ROM

AND

C

PP

1-Wire PORT

CONTROL LOGIC

1Kb

EEPROM

SCRATCHPAD 1

MAX31826

SCRATCHPAD 2

16-BIT TEMPERATURE REGISTER

8-BIT CRC GENERATOR

8-BIT CONFIGURATION REGISTER

ADDRESS PIN INPUT LATCH

AD0 AD1 AD2 AD3

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

MAX31826

1-Wire Digital Temperature Sensor

with 1Kb Lockable EEPROM

ABSOLUTE MAXIMUM RATINGS

Voltage Range on Any Pin Relative to Ground .... -0.5V to +4.5V

Continuous Power Dissipation (TA = +70NC)

FMAX (derate 4.5mW/NC above +70NC) .....................362mW

Operating Temperature Range ........................ -55NC to +125NC

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

(TA = -55°C to +125°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Supply Voltage V

Pullup Supply Voltage (Notes 2, 3)

Thermometer Error (Note 4) T

Input Logic-Low V

Input Logic-High (Notes 2, 6) V

Sink Current I

Standby Current I

Active Current I

Active Current with Communication

POR Time t

Input Leakage Current (AD0–AD3 Pins)

DQ Input Current I

DD

V

PU

ERR

DDS

DD

POR

DQ

Local power (Note 2) +3.0 +3.7 V

Parasite power +3.0 +3.7

Local power +3.0 V

-10NC to +85NC

-55NC to +125NC

(Notes 2, 5) -0.3 +0.8 V

IL

Local power +2.4

IH

Parasite power +3.0

V

L

= 0.4V (Note 2) 4.0 mA

I/O

(Notes 7, 8) 350 1000 nA

VDD = 3.7V (Note 9) 650 1200

Local or parasite power 4 7.8 ms

(Note 10) 5

Storage Temperature Range ............................ -55NC to +125NC

Lead Temperature (soldering, 10s) ................................+300NC

Soldering Temperature (reflow) ......................................+260NC

V

NC

V

FA

-0.5

Q0.25

-2 +2

lower

of 3.7V

(VDD +

0.3V)

lower

of 3.7V

(VDD +

0.3V)

800 1500

-1 +1

DD

+0.5

or

�� Maxim Integrated Products 2

MAX31826

1-Wire Digital Temperature Sensor

with 1Kb Lockable EEPROM

AC ELECTRICAL CHARACTERISTICS

(VDD = 3.0V to 3.7V, TA = -55°C to +125°C, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Temperature Conversion Time t

Time to Strong Pullup On t

Time Slot t

Recovery Time t

Write-Zero Low Time t

Write-One Low Time t

Read Data Valid t

Reset Time High t

Reset Time Low t

Presence-Detect High t

Presence-Detect Low t

DQ Capacitance C

AD0–AD3 Capacitance C

NONVOLATILE MEMORY

EEPROM Write/Erase Cycles N

EEPROM Data Retention t

EEPROM Write Time t

Note 1: Limits are 100% production tested at TA = +25°C and/or TA = +85°C. Limits over the operating temperature range and

relevant supply voltage range are guaranteed by design and characterization. Typical values are not guaranteed.

Note 2: All voltages are referenced to ground. Note 3: The pullup supply voltage specification assumes that the pullup device is ideal, and therefore the high level of the pullup

is equal to VPU. To meet the device’s VIH specification, 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: V

Note 4: Guaranteed by design. These limits represent a three sigma distribution. Note 5: To guarantee a presence pulse under low-voltage parasite-power conditions, V

as 0.5V.

Note 6: Logic-high voltages are specified at a 1mA source current. Note 7: Standby current specified up to TA = +70NC. Standby current typically is 3FA at TA = +125NC. Note 8: To minimize I Note 9: Active current refers to supply current during active temperature conversions or EEPROM writes. Note 10: DQ line is high (high-impedance state). Note 11: See the 1-Wire Timing Diagrams. Note 12: Under parasite power, if t

, DQ should be within the following ranges: V

DDS

CONV

SPON

SLOT

REC

LOW0

LOW1

RDV

RSTH

RSTL

PDHIGH

PDLOW

IN/OUT

IN_AD

EEWR

EEDR

WR

> 960Fs, a power-on reset (POR) can occur.

RSTL

12-bit resolution 150 ms

Start Convert T command, or Copy Scratchpad 2 command issued

(Note 11) 60 120

(Note 11) 1

(Note 11) 60 120

(Note 11) 1 15

(Note 11) 15

(Note 11) 480

(Notes 11, 12) 480

(Note 11) 15 60

(Note 11) 60 240

At TA = +25°C

At TA = +85°C (worst case)

GND

P VDQ P V

PU_ACTUAL

GND

200k

50k

40 Years

20 25 ms

= V

PU_IDEAL

might need to be reduced to as low

ILMAX

+ 0.3V or VDD - 0.3V P VDQ P VDD.

10

25 pF

50 pF

+ V

TRANSISTOR

Fs

.

�� Maxim Integrated Products 3

1-Wire WRITE-ZERO TIME SLOT

1-Wire READ-ZERO TIME SLOT

MAX31826

1-Wire Digital Temperature Sensor

with 1Kb Lockable EEPROM

1-Wire Timing Diagrams

t

REC

SLOT

t

LOW0

START OF NEXT CYCLE

1-Wire RESET PULSE

1-Wire PRESENCE DETECT

t

REC

t

RDV

RESET PULSE FROM HOST

t

RSTL

t

SLOT

t

PDHIGH

START OF NEXT CYCLE

t

RSTH

PRESENCE DETECT

t

PDLOW

�� Maxim Integrated Products 4

1-Wire Digital Temperature Sensor

(VCC = 3.3V, TA = -40°C, unless otherwise noted.)

THERMOMETER ERROR (˚C)

with 1Kb Lockable EEPROM

Typical Operating Characteristics

MAX31826 TYPICAL ERROR CURVE

0.5

0.4

0.3

0.2 MEAN ERROR

0.1

0

-0.1

-0.2

-0.3

-0.4

-0.5

-40 90

+3s ERROR

-3s ERROR

TEMPERATURE (˚C)

MAX31826

MAX31826 toc01

807050 60-10 0 10 20 30 40-30 -20

TOP VIEW

V

DD

Pin Configuration Pin Description

+

18AD3

27AD2DQ

MAX31826

µMAX

AD1N.C. 36

AD0GND 45

PIN NAME FUNCTION

1 V

Optional VDD. VDD must be grounded for

DD

operation in parasite-power mode.

Data Input/Output. Open-drain 1-Wire

2 DQ

interface pin. Also provides power to the device when used in parasite-power mode (see the Parasite Power section.)

3 N.C. No Connection. Not internally connected. 4 GND Ground

5 AD0

Location Address Input (Least Significant Bit)

6 AD1 Location Address Input 7 AD2 Location Address Input

8 AD3

Location Address Input (Most Significant Bit)

�� Maxim Integrated Products 5

MAX31826

1-Wire Digital Temperature Sensor

with 1Kb Lockable EEPROM

Detailed Description

The MAX31826 digital thermometer provides 12-bit temperature measurements and communicates over a 1-WireM bus that by definition requires only one data line (and ground) for communication with a central microcontroller. The data 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 MAX31826’s DQ pin). Four location address inputs simplify mapping of individual devices to specific locations.

Each device has a unique 64-bit serial code, allowing multiple devices to function on the same 1-Wire bus. Therefore, it is simple to use one microcontroller to control many devices distributed over a large area. In this bus system, the microcontroller 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 described in the 1-Wire Bus System section.

The Scratchpad 1 memory contains the 2-byte temperature register that stores the digital output from the temperature sensor. An additional 128 bytes (1Kb) of general-purpose EEPROM is included for storage of system data. The EEPROM can be locked to permanently prevent any further data writes.

The device can also operate without an external power supply. Power is instead supplied through the 1-Wire pullup resistor through DQ 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. Alternatively, a power supply on VDD can also power the device.

Measuring Temperature

The device’s core functionality is its direct-to-digital temperature sensor. The resolution of the temperature sensor is 12 bits, corresponding to a least significant bit value of 0.0625NC. The device powers up in a low-power idle state. To initiate a temperature measurement, the master must issue a Convert T command. Following the conversion, the resulting thermal data is stored in the 12-bit temperature register in the Scratchpad 1 memory and the device returns to its idle state. If the device is powered by an external supply, the master can issue read time slots (see the 1-Wire Bus System section) after the Convert T command, and the device responds by transmitting 0 while the temperature conversion is in progress and 1 when the conversion is done. If the device is powered with parasite power, this notification technique cannot be used because the bus must be pulled high by a strong pullup during the entire temperature conversion. The bus requirements for parasite power are explained in the

Powering the MAX31826 section.

The temperature data (in NC) is stored as a 16-bit signextended two’s complement number in the temperature register (see the Temperature Register Format). The sign bits (S) indicate if the temperature is positive or negative; for positive numbers S = 0 and for negative numbers S = 1. Table 1 gives examples of digital output data and the corresponding temperature readings.

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

MSB

LSB

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

S S S S S 2

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

3

2

�� Maxim Integrated Products 6

2

1

2

Temperature Register Format

6

0

-1

2

-2

2

5

2

-3

2

4

2

-4

2

1-Wire Digital Temperature Sensor

Table 1. Temperature/Data Relationship

MAX31826

with 1Kb Lockable EEPROM

TEMPERATURE (NC)

+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

DIGITAL OUTPUT (BINARY) DIGITAL OUTPUT (HEX)

Powering the MAX31826

The MAX31826 can be powered by an external supply on the VDD pin, or it can operate in “parasite power” mode, which allows the device to function without a local external supply. Parasite power is 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 DQ 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 parasitepower capacitor (CPP) to provide power when the bus is low. When the device is used in parasite-power mode, VDD must be connected to ground.

In parasite-power mode, the 1-Wire bus and CPP can provide sufficient current to the device for most operations as long as the specified timing and voltage requirements are met (see the DC Electrical Characteristics and the

AC Electrical Characteristics tables). However, when the

device is performing temperature conversions or copying data from the Scratchpad 2 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 when data is being copied from the Scratchpad 2 to EEPROM. This can be accomplished by using a MOSFET to pull the bus directly to the rail as shown in Figure 1. The 1-Wire bus must be switched to

the strong pullup within 10Fs (max) after a Convert T or Copy Scratchpad 2 command is issued, and the bus must be held high by the pullup for the duration of the conversion (t (tWR). No other activity can take place on the 1-Wire bus while the pullup is enabled.

The device can also be powered by the conventional method of connecting an external power supply to VDD, as shown in Figure 2. The advantage of this method is that the MOSFET pullup is not required, and the 1-Wire bus is free to carry other traffic during the temperature conversion period or EEPROM write time.

The use of parasite power is not recommended for temperatures above 100NC because the device may not be able to sustain communications due to the higher leakage currents that can exist at these temperatures. For applications in which such temperatures are likely, it is strongly recommended that the device be powered by an external power supply.

In some situations the bus master might not know whether the devices on the bus are parasite powered or powered by external supplies. The master needs this information to determine if the strong bus pullup should be used during temperature conversions. To get this information, the master can issue a Skip ROM command, followed by a Read Power Supply command, followed by a read time slot. During the read time slot, parasite-powered devices pull the bus low, and externally powered devices let the bus remain high. If the bus is pulled low, the master knows that it must supply the strong pullup on the 1-Wire bus during temperature conversions or EEPROM writes.

) or the duration of the EEPROM write

CONV

�� Maxim Integrated Products 7