MAXIM DS1825 User Manual

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DS1825

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FEATURES

§ Unique 1-WireÒ Interface Requires Only One
Port Pin for Communication

§ Each Device has a Unique 64-Bit Serial Code
Stored in an On-Board ROM

§ Multidrop Capability Simplifies Distributed
Temperature-Sensing Applications

§ 4 Pin-Programmable Bits to Uniquely Identify
Up to 16 Sensor Locations on a Bus

§ Requires No External Components

§ Can be Powered from Data Line. Power Supply

Range: 3.0V to 3.7V

§ 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 Digital Word in
750ms (max)

§ User-Definable (NV) Alarm Settings

§ Alarm Search Command Identifies and

Addresses Devices Whose Temperature is
Outside of Programmed Limits (Temperature
Alarm Condition)

§ Available in 8-Pin mSOP Package

§ Software Compatible with the DS1822

1-Wire is a registered trademark of Dallas Semiconductor.

Programmable Resolution 1-Wire

Digital Thermometer With 4-Bit ID

PIN ASSIGNMENT

V

DQ

N.C.

GND

DD

1

2

DS1825

3

8-pin mSOP

DS1825U)

4

µSOP

(DS1825U)

8

7

6

5

D3

D2

D1

D0

PIN DESCRIPTION

GND - Ground
DQ - Data In/Out
N.C. - No Connect
V

- Power Supply Voltage

DD

AD0 to AD3 - Address Pins

APPLICATIONS

Thermostatic Controls
Industrial Systems
Consumer Products
Thermometers
Thermally-Sensitive Systems

DESCRIPTION

The DS1825 digital thermometer provides 9 to 12-bit centigrade temperature measurements and has an alarm
function with NV user-programmable upper and lower trigger points. The DS1825 communicates over a 1-Wire bus
that by definition requires only one data 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
addition, the DS1825 can derive power directly from the data line (“parasite power”), eliminating the need for an
external power supply.

ORDERING INFORMATION

ORDERING NUMBER PACKAGE MARKING DESCRIPTION

DS1825U 1825 8-pin µSOP
DS1825U/T&R 1825 8-pin µSOP Tape-and-Reel
DS1825U+ 1825 (See Note 1)
DS1825U+T&R 1825 (See Note 1) 8-pin µSOP Tape-and-Reel, Lead Free
Note 1: Additionally, a "+" symbol will be marked on the package.

8-pin mSOP, Lead Free

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DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

DESCRIPTION (cont.)

Each DS1825 has a unique 64-bit serial code, which allows multiple DS1825s to function on the same 1-Wire bus;
thus, it is simple to use one microprocessor to control many DS1825s distributed over a large area. In addition, the
4-bit location address can be used to identify specific temperature sensors in the system without requiring a wide
lookup table. 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.

ABSOLUTE MAXIMUM RATINGS*

Voltage on Any Pin Relative to Ground -0.5V to +6.0V
Operating Temperature Range -55
Storage Temperature Range -55
Solder Dip Temperature (10s) +260
Reflow Oven Temperature +220

These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation
sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.

°

C to +125°C

°

C to +125°C

°

C

°

C

DC ELECTRICAL CHARACTERISTICS (-55°C to +125°C; VDD= 3.0V to 3.7V)

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

Supply Voltage VDD Local Power +3.0 +3.7 V 1

Pullup Supply Voltage VPU

Thermometer Error t

Programming
Resistor: AD0-AD3
DQ Input Logic Low V

DQ Input Logic High V

ERR

R

PGM

IL(DQ)

IH(DQ)

Parasite Power +3.0 +3.7

Local Power +3.0 V

DD

-10°C to +85°C ±0.5 °C

-55°C to +125°C ±2 °C

0 10

V 1, 2

3

kW

12

-0.3 +0.7 V 1, 4, 5

The lower of

3.7
or
+ 0.3

V

DD

V 1, 6

Local Power +2.2

Parasite Power +3.0

Sink Current IL V
Standby Current I

500 1000 nA 7, 8

DDS

Active Current IDD V
DQ Input Current I

DQ

= 0.4V 4.0 mA 1

I/O

= 3.7V 0.65 1.5 mA 9

DD

5 µA 10

Drift ±0.2 °C 11

NOTES:

1. All voltages are referenced to ground.

2. The Pullup Supply Voltage specification assumes that the pullup device is ideal, and therefore the high level of the pullup is equal to V
In order to meet the V
across the transistor when it is turned on; thus: V

3. See typical performance curve in Figure 18

4. Logic low voltages are specified at a sink current of 4mA.

5. To guarantee a presence pulse under low voltage parasite power conditions, V

6. Logic high voltages are specified at a source current of 1mA.

7. Standby current specified up to 70°C. Standby current typically is 3mA at 125°C.

8. To minimize I

9. Active current refers to supply current during active temperature conversions or EEPROM writes.

10. DQ line is high (“hi-Z” state).

11. Drift data is based on a 1000 hour stress test at 125°C.

12. Inputs AD0-AD3 must be tied either High or Low. A "Low" is a connection to the GND terminal. A "High" connection varies with usage of
the DS1825. When connected as a parasite powered sensor, a connection to DQ is considered a High. When powered through the V
pin, a connection to V
Figures 20 and 21 for details. When optional programming resistors are used, their maximum values are 10,000W.

DDS

spec of the DS1825, the actual supply rail for the strong pullup transistor must include margin for the voltage drop

IH

, DQ should be within the following ranges: GND £ DQ £ GND + 0.3V or VDD - 0.3V £ DQ £ VDD.

is a High. If left floating, the input values are indeterminate and may be either logical "0" or logical "1." See

DD

PU_ACTUAL

= V

PU_IDEAL

+ V

TRANSISTOR

.

may have to be reduced to as low as 0.5V.

ILMAX

.

PU

DD

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DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

AC ELECTRICAL CHARACTERISTICS: NV MEMORY

(-55°C to +100°C; V

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS

NV Write Cycle Time twr 2 10 ms
EEPROM Writes N
EEPROM Data Retention t

-55°C to +55°C 50k writes

EEWR

-55°C to +55°C 10 years

EEDR

= 3.0V to 3.7V)

DD

AC ELECTRICAL CHARACTERISTICS (-55°C to +125°C; V

PARAMETER SYMBOL CONDITION MIN TYP MAX UNITS NOTES

9-bit resolution 93.75 ms 1
Temperature Conversion
Time

t

CONV

10-bit resolution 187.5 ms 1
11-bit resolution 375 ms 1
12-bit resolution 750 ms 1

Time to Strong Pullup On t

Time Slot t
Recovery Time t
Write 0 Low Time t
Write 1 Low Time t
Read Data Valid t
Reset Time High t
Reset Time Low t
Presence Detect High t
Presence Detect Low t
Capacitance: DQ C
Capacitance: AD0-AD3 C

SPON

60 120 µs 1

SLOT

1 µs 1

REC

60 120 µs 1

LOW0

1 15 µs 1

LOW1

15 µs 1

RDV

480 µs 1

RSTH

480 µs 1, 2

RSTL

15 60 µs 1

PDHIGH

60 240 µs 1

PDLOW

25 pF

IN/OUT

50 pF

IN_AD

Start Convert T

Command Issued

10 µs

NOTES:

1. Refer to timing diagrams in Figure 18.

2. Under parasite power, if t

> 960ms, a power on reset may occur.

RSTL

Table 1. DETAILED PIN DESCRIPTIONS

PIN SYMBOL DESCRIPTION

4 GND

2

DQ

1

V

DD

5 AD0

6 AD1

7 AD2

8 AD3

3 N.C.

Ground.

Data Input/Output pin. Open-drain 1-Wire interface pin. Also

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

Optional V

power mode.

pin. VDD must be grounded for operation in parasite

DD

Location Address Input Pin LSB

Location Address Input Pin

Location Address Input Pin

Location Address Input Pin MSB

No Connection

= 3.0V to 3.7V)

DD

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DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

OVERVIEW

Figure 1 shows a block diagram of the DS1825, and pin descriptions are given in Table 1. The 64-bit ROM stores
the device’s unique serial code. The scratchpad memory contains the 2-byte temperature register that stores the
digital output from the temperature sensor. In addition, the scratchpad provides access to the 1-byte upper and
lower alarm trigger registers (T

and TL), and the 1-byte configuration register. The configuration register allows the

H

user to set the resolution of the temperature-to-digital conversion to 9, 10, 11, or 12 bits. It is also used for the hard­wired address programmed by the AD0-AD3 pins. The T

, TL, and configuration registers are NV (EEPROM), so

H

they will retain data when the device is powered down.

The DS1825 uses Dallas’ 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 3-state or
open-drain port (the DQ pin in the case of the DS1825). 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 of this data sheet.

Another feature of the DS1825 is the ability to 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 (C

), which then supplies power to the device when the bus is low. This method of deriving

PP

power from the 1-Wire bus is referred to as “parasite power.” As an alternative, the DS1825 can also be powered
by an external supply on V

DD

.

Figure 1. DS1825 BLOCK DIAGRAM

V

PULLUP

4.7k

DQ

GND

V

DD

Parasite

Power
Circuit

Cpp

Pow er

Supply

Sen se

64-Bit ROM

And

1-wire Port

Memory

Control Logic

S
C
R
A
T
C
P
A
D

16-bit Temp Reg

8-bit TH Register

8-bit TL Register

8-bit CRC Gen

8-bit Config. Reg

Address Pin

Input Latch

AD0-AD3

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DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

OPERATION¾MEASURING TEMPERATURE

The core functionality of the DS1825 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, respectively. The default resolution at power-up is 12-bit. The DS1825 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 12-bit temperature register in the
scratchpad memory and the DS1825 returns to its idle state. If the DS1825 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
DS1825 will respond by transmitting 0 while the temperature conversion is in progress and 1 when the conversion
is done. If the DS1825 is powered with parasite power, this notification technique cannot be used since the bus
must be pulled high by a strong pullup during the entire temperature conversion. The bus requirements for parasite
power are explained in detail in the POWERING THE DS1825 section of this data sheet.

The DS1825 output temperature data is calibrated in degrees centigrade; 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 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 DS1825 is configured for 12­bit 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 3 gives
examples of digital output data and the corresponding temperature reading for 12-bit resolution conversions.

Figure 2. TEMPERATURE REGISTER FORMAT

LS Byte

MS Byte

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

3

2

2

bit 15

S S S S S 2

2

2

1

2

0

2

-1

2

-2

2

-3

2

bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8

6

2

5

2

-4

4

Table 3. TEMPERATURE/DATA RELATIONSHIP

TEMPERATURE

DIGITAL OUTPUT

(Binary)

+125°C 0000 0111 1101 0000 07D0h

+85°C* 0000 0101 0101 0000 0550h

+25.0625°C 0000 0001 1001 0001 0191h

+10.125°C 0000 0000 1010 0010 00A2h

+0.5°C 0000 0000 0000 1000 0008h

0°C 0000 0000 0000 0000 0000h

-0.5°C 1111 1111 1111 1000 FFF8h

-10.125°C 1111 1111 0101 1110 FF5Eh

-25.0625°C 1111 1110 0110 1111 FE6Fh

-55°C 1111 1100 1001 0000 FC90h

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

DIGITAL OUTPUT

(Hex)

OPERATION¾ALARM SIGNALING

After the DS1825 performs a temperature conversion, the temperature value is compared to the user-defined two’s
complement alarm trigger values stored in the 1-byte T
the value is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. The T
registers are NV (EEPROM) so they will retain data when the device is powered down. T
through bytes 2 and 3 of the scratchpad as explained in the MEMORY section of this data sheet.

and TL registers (see Figure 3). The sign bit (S) indicates if

H

and TL can be accessed

H

and TL

H

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DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

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 2

5

2

5

2

5

2

2

2

1

2

0

Only bits 11 through 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 T
exists and an alarm flag is set inside the DS1825. This flag is updated after every temperature measurement;
therefore, if the alarm condition goes away, the flag will be turned off after the next temperature conversion.

The master device can check the alarm flag status of all DS1825s on the bus by issuing an Alarm Search [ECh]
command. Any DS1825s with a set alarm flag will respond to the command, so the master can determine exactly
which DS1825s have experienced an alarm condition. If an alarm condition exists and the T
changed, another temperature conversion should be done to validate the alarm condition.

or higher than or equal to TH, an alarm condition

L

or TL settings have

H

POWERING THE DS1825

The DS1825 can be powered by an external supply on the VDD pin, or it can operate in “parasite power” mode,
which allows the DS1825 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 DS1825’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 DS1825 while the bus is high, and some of the charge is stored on the parasite
power capacitor (C
the V

pin must be connected to ground.

DD

In parasite power mode, the 1-Wire bus and CPP can provide sufficient current to the DS1825 for most operations
as long as the specified timing and voltage requirements are met (refer to the DC ELECTRICAL
CHARACTERISTICS and the AC ELECTRICAL CHARACTERISTICS sections of this data sheet). However, when
the DS1825 is performing temperature conversions or copying 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 C
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 must be switched to the strong
pullup within 10ms (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 (t
take place on the 1-Wire bus while the pullup is enabled.

) to provide power when the bus is low. When the DS1825 is used in parasite power mode,

PP

. To assure that the DS1825 has sufficient

PP

) or data transfer (t

conv

= 10ms). No other activity can

wr

The DS1825 can also be powered by the conventional method of connecting an external power supply to the V

DD

pin, as shown in Figure 5. 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 time.

The use of parasite power is not recommended for temperatures above 100°C since the DS1825 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 DS1825 be powered by an
external power supply.

In some situations the bus master may not know whether the DS1825s 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 [CCh] command
followed by a Read Power Supply [B4h] command followed by a “read time slot”. During the read time slot, parasite
powered DS1825s will pull the bus low, and externally powered DS1825s will 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.

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DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID

Figure 4. SUPPLYING THE PARASITE-POWERED DS1825 DURING
TEMPERATURE CONVERSIONS

Micro-

processor

VPU

4.7K

VPU

1-Wire Bus

DS1825

GND

V

DQ

DD

To Other
1-Wire

Figure 5. POWERING THE DS1825 WITH AN EXTERNAL SUPPLY

Micro-

processor

VPU

4.7K

1-Wire Bus

DS1825

GND

V

VDD (External Supply)

DQ

DD

To Other
1-Wire

Devices

Devices

64-BIT LASERED ROM CODE

Each DS1825 contains a unique 64-bit code (see Figure 6) stored in ROM. The least significant 8 bits of the ROM
code contain the DS1825’s 1-Wire family code: 3Bh. 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 DS1825 to operate as a 1-Wire device using the protocol
detailed in the 1-Wire BUS SYSTEM section of this data sheet.

Figure 6. 64-BIT LASERED ROM CODE

8-BIT CRC 48-BIT SERIAL NUMBER 8-BIT FAMILY CODE (3Bh)

MSB MSB LSB LSB LSBMSB

MEMORY

The DS1825’s memory is organized as shown in Figure 7. The memory consists of an SRAM scratchpad with NV
EEPROM storage for the high and low alarm trigger registers (T
DS1825 alarm function is not used, the T
commands are described in detail in the DS1825 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 T
data, which is explained in detail in the CONFIGURATION REGISTER section of this data sheet. Bytes 5, 6, and 7
are reserved for internal use by the device and cannot be overwritten.

and TL registers can serve as general-purpose memory. All memory

H

and TL registers. Byte 4 contains the configuration register

H

and TL) and configuration register. Note that if the

H

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