DS1825
Programmable Resolution 1-Wire
Digital Thermometer With 4-Bit ID
www.maxim-ic.com
FEATURES
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Unique 1-Wire 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
Ò
PIN ASSIGNMENT
V
DD
DQ
N.C.
GND
1
8
AD3
AD2
AD1
AD0
2
7
DS1825
3
6
8-pin
mSOP
(DS1825U)
5
4
µSOP
(DS1825U)
PIN DESCRIPTION
GND
DQ
N.C.
V
DD
AD0 to AD3
- Ground
- Data In/Out
- No Connect
- Power Supply Voltage
- Address Pins
APPLICATIONS
1-Wire is a registered trademark of Dallas Semiconductor.
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)
8-pin
mSOP,
Lead Free
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.
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Rev 020105
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
Operating Temperature Range
Storage Temperature Range
Solder Dip Temperature (10s)
Reflow Oven Temperature
-0.5V to +6.0V
-55
°
C to +125°C
-55
°
C to +125
°
C
+260
°
C
+220
°
C
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.
DC ELECTRICAL CHARACTERISTICS
PARAMETER
Supply Voltage
Pullup Supply Voltage
Thermometer Error
Programming
Resistor: AD0-AD3
DQ Input Logic Low
DQ Input Logic High
SYMBOL
V
DD
V
PU
t
ERR
R
PGM
V
IL(DQ)
Local Power
V
IH(DQ)
Parasite Power
Sink Current
Standby Current
Active Current
DQ Input Current
Drift
I
L
I
DDS
I
DD
I
DQ
V
I/O
= 0.4V
V
DD
= 3.7V
CONDITION
Local Power
Parasite Power
Local Power
-10°C to +85°C
-55°C to +125°C
MIN
+3.0
+3.0
+3.0
(-55°C to +125°C; V
DD
= 3.0V to 3.7V)
TYP
MAX
+3.7
+3.7
V
DD
±0.5
±2
10
+0.7
The lower of
3.7
or
V
DD
+ 0.3
500
0.65
5
±0.2
1000
1.5
UNITS
V
V
°C
°C
kW
V
V
NOTES
1
1, 2
3
12
1, 4, 5
1, 6
0
-0.3
+2.2
+3.0
4.0
mA
nA
mA
µA
°C
1
7, 8
9
10
11
NOTES:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
All voltages are referenced to ground.
The Pullup Supply Voltage specification assumes that the pullup device is ideal, and therefore the high level of the pullup is equal to V
PU
.
In order to meet the V
IH
spec of the DS1825, 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
PU_ACTUAL
= V
PU_IDEAL
+ V
TRANSISTOR
.
See typical performance curve in Figure 18
Logic low voltages are specified at a sink current of 4mA.
To guarantee a presence pulse under low voltage parasite power conditions, V
ILMAX
may have to be reduced to as low as 0.5V.
Logic high voltages are specified at a source current of 1mA.
Standby current specified up to 70°C. Standby current typically is 3mA at 125°C.
To minimize I
DDS
, DQ should be within the following ranges: GND
£
DQ
£
GND + 0.3V or V
DD
- 0.3V
£
DQ
£
V
DD
.
Active current refers to supply current during active temperature conversions or EEPROM writes.
DQ line is high (“hi-Z” state).
Drift data is based on a 1000 hour stress test at 125°C.
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
DD
pin, a connection to V
DD
is a High. If left floating, the input values are indeterminate and may be either logical "0" or logical "1." See
Figures 20 and 21 for details. When optional programming resistors are used, their maximum values are 10,000W.
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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
DD
= 3.0V to 3.7V)
PARAMETER
NV Write Cycle Time
EEPROM Writes
EEPROM Data Retention
SYMBOL
t
wr
N
EEWR
t
EEDR
CONDITION
MIN
50k
10
TYP
2
MAX
10
-55°C to +55°C
-55°C to +55°C
UNITS
ms
writes
years
AC ELECTRICAL CHARACTERISTICS
PARAMETER
Temperature Conversion
Time
Time to Strong Pullup On
Time Slot
Recovery Time
Write 0 Low Time
Write 1 Low Time
Read Data Valid
Reset Time High
Reset Time Low
Presence Detect High
Presence Detect Low
Capacitance: DQ
Capacitance: AD0-AD3
SYMBOL
t
CONV
t
SPON
t
SLOT
t
REC
t
LOW0
t
LOW1
t
RDV
t
RSTH
t
RSTL
t
PDHIGH
t
PDLOW
C
IN/OUT
C
IN_AD
CONDITION
9-bit resolution
10-bit resolution
11-bit resolution
12-bit resolution
Start Convert T
Command Issued
(-55°C to +125°C; V
DD
= 3.0V to 3.7V)
MIN
TYP
MAX
93.75
187.5
375
750
10
120
120
15
15
60
240
25
50
UNITS
ms
ms
ms
ms
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
pF
pF
NOTES
1
1
1
1
1
1
1
1
1
1
1, 2
1
1
60
1
60
1
480
480
15
60
NOTES:
1.
2.
Refer to timing diagrams in Figure 18.
Under parasite power, if t
RSTL
> 960ms, a power on reset may occur.
Table 1. DETAILED PIN DESCRIPTIONS
PIN
4
2
DQ
1
5
6
7
8
3
V
DD
AD0
AD1
AD2
AD3
N.C.
SYMBOL
GND
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
DD
pin.
V
DD
must be grounded for operation in parasite
power mode.
Location Address Input Pin LSB
Location Address Input Pin
Location Address Input Pin
Location Address Input Pin MSB
No Connection
DESCRIPTION
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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
H
and T
L
), and the 1-byte configuration register. The configuration register allows the
user to set the resolution of the temperature-to-digital conversion to 9, 10, 11, or 12 bits. It is also used for the hard-
wired address programmed by the AD0-AD3 pins. The T
H
, T
L
, and configuration registers are NV (EEPROM), so
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
PP
), 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.” 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
Memory
Control Logic
DQ
Parasite
Power
Circuit
GND
Cpp
64-Bit ROM
And
1-wire Port
V
DD
Power
Supply
Sense
S
C
R
A
T
C
P
A
D
16-bit Temp Reg
8-bit T
H
Register
8-bit T
L
Register
8-bit CRC Gen
8-bit Config. Reg
Address Pin
Input Latch
AD0-AD3
4 of 21
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 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 3 gives
examples of digital output data and the corresponding temperature reading for 12-bit resolution conversions.
Figure 2. TEMPERATURE REGISTER FORMAT
bit 7
LS Byte
2
3
bit 6
2
2
bit 5
2
1
bit 4
2
0
bit 3
2
-1
bit 2
2
-2
bit 1
2
-3
bit 0
2
-4
bit 15
MS Byte
S
bit 14
S
bit 13
S
bit 12
S
bit 11
S
bit 10
2
6
bit 9
2
5
bit 8
2
4
Table 3. TEMPERATURE/DATA RELATIONSHIP
TEMPERATURE
+125°C
+85°C*
+25.0625°C
+10.125°C
+0.5°C
0°C
-0.5°C
-10.125°C
-25.0625°C
DIGITAL OUTPUT
(Binary)
0000 0111 1101 0000
0000 0101 0101 0000
0000 0001 1001 0001
0000 0000 1010 0010
0000 0000 0000 1000
0000 0000 0000 0000
1111 1111 1111 1000
1111 1111 0101 1110
1111 1110 0110 1111
DIGITAL OUTPUT
(Hex)
07D0h
0550h
0191h
00A2h
0008h
0000h
FFF8h
FF5Eh
FE6Fh
-55°C
1111 1100 1001 0000
FC90h
*The power-on reset value of the temperature register is +85°C
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
H
and T
L
registers (see Figure 3). The sign bit (S) indicates if
the value is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. The T
H
and T
L
registers are NV (EEPROM) so they will retain data when the device is powered down. T
H
and T
L
can be accessed
through bytes 2 and 3 of the scratchpad as explained in the
MEMORY
section of this data sheet.
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