DS1821 Maxim Integrated Products, DS1821 Datasheet - Page 4
![IC THERMOMETER/STAT PROG 3-PR35](/photos/7/26/72615/406-3-pr35_sml.jpg)
DS1821
Manufacturer Part Number
DS1821
Description
IC THERMOMETER/STAT PROG 3-PR35
Manufacturer
Maxim Integrated Products
Datasheet
1.DS1821.pdf
(18 pages)
Specifications of DS1821
Function
Thermometer, Thermostat
Topology
Comparator, Register Bank
Sensor Type
Internal
Sensing Temperature
-55°C ~ 125°C
Output Type
Digital
Output Alarm
No
Output Fan
No
Voltage - Supply
2.7 V ~ 5.5 V
Operating Temperature
-55°C ~ 125°C
Mounting Type
Through Hole
Package / Case
TO-92-3 (Long Body), TO-226
Full Temp Accuracy
+/- 1 C
Digital Output - Bus Interface
Serial (1-Wire)
Digital Output - Number Of Bits
8 bit
Maximum Operating Temperature
+ 125 C
Minimum Operating Temperature
- 55 C
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
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TEMPERATURE MEASURING CIRCUITRY Figure 2
OPERATING MODES
The DS1821 has two operating modes: 1-Wire mode and thermostat mode. The power-up operating
mode is determined by the user-programmable T/R ¯ bit in the status/configuration register: if T/R ¯ = 0 the
device powers-up in 1-Wire mode, and if T/R ¯ = 1 the device powers-up in thermostat mode. The T/R ¯ bit
is stored in nonvolatile memory (EEPROM), so it will retain its value when the device is powered down.
1-Wire MODE
The DS1821 arrives from the factory in 1-Wire mode (T/R ¯ = 0). In this mode, the DQ pin of the DS1821
is configured as a 1-Wire port for communication with a microprocessor using the protocols described in
the 1-Wire BUS SYSTEM section of this datasheet. These communications can include reading and
writing the high and low thermostat trip-point registers (T
reading the temperature, counter, and slope accumulator registers. Also in this mode, the microprocessor
can initiate and stop temperature measurements as described in the OPERATION – MEASURING
TEMPERATURE section of this datasheet.
The T
register are stored in nonvolatile EEPROM memory, so they will retain data when the device is powered
down. This allows these registers to be pre-programmed when the DS1821 is to be used as a standalone
thermostat.
writes to nonvolatile memory should be initiated while a write to nonvolatile memory is in progress.
H
COEFFICIENT OSCILLATOR
and T
COEFFICIENT OSCILLATOR
LOW TEMPERATURE
PRESET
HIGH TEMPERATURE
Writes to these nonvolatile registers can take up to 10ms. To avoid data corruption, no
L
registers and certain bits (THF, TLF, T/R ¯ , POL and 1SHOT) in the status/configuration
SLOPE ACCUMULATOR
COUNTER
COUNTER
4 of 18
=0
=0
H
and T
INC
STOP
L
) and the configuration register, and
PRESET
TEMPERATURE REGISTER
COMPARE
SET/CLEAR
LSB