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PDF DS18S20 Data sheet ( Hoja de datos )
| Número de pieza | DS18S20 | |
| Descripción | High-Precision 1-Wire Digital Thermometer | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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AVAILABLE
DS18S20
High-Precision 1-Wire Digital Thermometer
FEATURES
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
Requires No External Components
Can Be Powered from Data Line. Power
Supply Range is 3.0V to 5.5V
Measures Temperatures from -55°C to
+125°C (-67°F to +257°F)
±0.5°C Accuracy from -10°C to +85°C
9-Bit Thermometer Resolution
Converts Temperature 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)
Applications Include Thermostatic Controls,
Industrial Systems, Consumer Products,
Thermometers, or FAunynTchteiromnaallly DSeinasgitirvaems
System
PIN CONFIGURATIONS
MAXIM
DS1820
123
N.C.
N.C.
VDD
DQ
1
2
3
4
8 N.C.
7 N.C.
6 N.C.
5 GND
SO (150 mils)
(DS18S20Z)
12 3
(BOTTOM VIEW)
TO-92
(DS18S20)
DESCRIPTION
The DS18S20 digital thermometer provides 9-bit Celsius temperature measurements and has an alarm
function with nonvolatile user-programmable upper and lower trigger points. The DS18S20
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 DS18S20 can derive power
directly from the data line (“parasite power”), eliminating the need for an external power supply.
Each DS18S20 has a unique 64-bit serial code, which allows multiple DS18S20s to function on the same
1-Wire bus. Thus, it is simple to use one microprocessor to control many DS18S20s distributed over a
large area. Applications that can benefit from this feature include HVAC environmental controls,
temperature monitoring systems inside buildings, equipment, or machinery, and process monitoring and
coPnitnroClonsfyigsuteramtiosn. s appear at end of data sheet.
Functional Diagrams continued at end of data sheet.
1-WUiCreSiPs aisraegtriastdeeremdatrrkadoef mMaarxkimof IMntaexgimratIendtePgrraotdeudcPtsr,oIdnucc.ts, Inc.
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
19-5474; Rev 8/10
Free Datasheet http://www.datasheet4u.com/
1 page  
DS18S20
POWERING THE DS18S20
The DS18S20 can be powered by an external supply on the VDD pin, or it can operate in “parasite power”
mode, which allows the DS18S20 to function without a local external supply. Parasite power is very
useful for applications that require remote temperature sensing or those with space constraints.
Figure 1 shows the DS18S20’s parasite-power control circuitry, which “steals” power from the 1-Wire
bus via the DQ pin when the bus is high. The stolen charge powers the DS18S20 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. When the DS18S20 is used in parasite power mode, the VDD pin must be connected to ground.
In parasite power mode, the 1-Wire bus and CPP can provide sufficient current to the DS18S20 for most
operations as long as the specified timing and voltage requirements are met (see the DC Electrical
Characteristics and the AC Electrical Characteristics). However, when the DS18S20 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 CPP. To assure that the DS18S20 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 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 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.
The DS18S20 can also be powered by the conventional method of connecting an external power supply to
the VDD 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 DS18S20 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 DS18S20 be
powered by an external power supply.
In some situations the bus master may not know whether the DS18S20s 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 DS18S20s will pull the bus low, and externally powered
DS18S20s 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.
5 of 23
5 Page 
DS18S20
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 DS18S20s 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 DS18S20s 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 Operation—Alarm Signaling section
for an explanation of alarm flag operation.
DS18S20 FUNCTION COMMANDS
After the bus master has used a ROM command to address the DS18S20 with which it wishes to
communicate, the master can issue one of the DS18S20 function commands. These commands allow the
master to write to and read from the DS18S20’s scratchpad memory, initiate temperature conversions and
determine the power supply mode. The DS18S20 function commands, which are described below, are
summarized in Table 2 and illustrated by the flowchart in Figure 15.
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 DS18S20 returns to its
low-power idle state. If the device is being used in parasite power mode, 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 Powering the DS18S20 section. If the DS18S20 is powered by an
external supply, the master can issue read-time slots after the Convert T command and the DS18S20 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 2 bytes of data to the DS18S20’s scratchpad. The first byte is
written into the TH register (byte 2 of the scratchpad), and the second byte is written into the TL register
(byte 3 of the scratchpad). Data must be transmitted least significant bit first. Both 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 scratchpad until the 9th byte (byte 8 – CRC) is
read. The master may issue a reset to terminate reading at any time if only part of the scratchpad data is
needed.
11 of 23
11 Page | ||
| Páginas | Total 23 Páginas | |
| PDF Descargar | [ Datasheet DS18S20.PDF ] | |
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