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PDF DS1825 Data sheet ( Hoja de datos )
| Número de pieza | DS1825 | |
| Descripción | Programmable Resolution 1-Wire Digital Thermometer | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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DS1825
Programmable Resolution 1-Wire
Digital Thermometer With 4-Bit ID
www.maxim-ic.com
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.
PIN ASSIGNMENT
VDD
DQ
N.C.
GND
18
27
DS1825
3 8-pin mSOP6
(DS1825U)
45
µSOP
(DS1825U)
AD3
AD2
AD1
AD0
PIN DESCRIPTION
GND
- Ground
DQ - Data In/Out
N.C.
- No Connect
VDD
AD0 to AD3
- Power Supply Voltage
- 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+
DS1825U+T&R
1825 (See Note 1)
1825 (See Note 1)
8-pin mSOP, Lead Free
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
1 page  
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
LS Byte
bit 7
23
bit 6
22
bit 5
21
bit 4
20
bit 3
2-1
bit 2
2-2
bit 1
2-3
bit 0
2-4
MS Byte
bit 15
S
bit 14
S
bit 13
S
bit 12
S
bit 11
S
bit 10
26
bit 9
25
Table 3. TEMPERATURE/DATA RELATIONSHIP
TEMPERATURE
+125°C
DIGITAL OUTPUT
(Binary)
0000 0111 1101 0000
DIGITAL OUTPUT
(Hex)
07D0h
+85°C*
+25.0625°C
+10.125°C
+0.5°C
0°C
-0.5°C
-10.125°C
-25.0625°C
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
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
bit 8
24
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 TH and TL 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 TH and TL
registers are NV (EEPROM) so they will 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 of this data sheet.
5 of 21
5 Page 
DS1825 Programmable Resolution 1-Wire Digital Thermometer With 4-Bit ID
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 of the slave devices. If there is
only one slave on the bus, the simpler Read ROM command (see below) can be used in place of the Search ROM
process. For a detailed explanation of the Search ROM procedure, refer to the iButtonÒ Book of Standards at
www.ibutton.com/ibuttons/standard.pdf. 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 procedure. If this command is used when there is more than one
slave present on the bus, a data collision will occur when all the slaves attempt to respond at the same time.
MATCH ROM [55h]
The match ROM 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
will respond to the function command issued by the master; all other slaves on the bus will 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 DS1825s 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 sending the
device’s 64-bit ROM code. A Skip ROM command followed by a Read Scratchpad command will cause a data
collision on the bus if there is more than one slave since multiple devices will attempt to transmit data
simultaneously.
ALARM SEARCH [ECh]
The operation of this command is identical to the operation of the Search ROM command except that only slaves
with a set alarm flag will respond. This command allows the master device to determine if any DS1825s
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. Refer to the OPERATION¾ALARM SIGNALING section for an explanation of alarm flag
operation.
DS1825 FUNCTION COMMANDS
After the bus master has used a ROM command to address the DS1825 with which it wishes to communicate, the
master can issue one of the DS1825 function commands. These commands allow the master to write to and read
from the DS1825’s scratchpad memory, initiate temperature conversions and determine the power supply mode.
The DS1825 function commands, which are described below, are summarized in Table 5 and illustrated by the
flowchart in Figure 12.
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 scratchpad memory and the DS1825 returns to its low-power idle
state. If the device is being used in parasite power mode, within 10ms (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
POWERING THE DS1825 section. If the DS1825 is powered by an external supply, the master can issue read time
slots 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. In parasite power mode this notification technique
cannot be used since the bus is pulled high by the strong pullup during the conversion.
WRITE SCRATCHPAD [4Eh]
This command allows the master to write 3 bytes of data to the DS1825’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.
iButton is a registered trademark of Dallas Semiconductor.
11 of 21
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet DS1825.PDF ] | |
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