DS1821S Maxim Integrated Products, DS1821S Datasheet - Page 4

• Manufacturer Part Number: DS1821S
• Description: IC THERMOMETER/STAT PROG 8-SOIC
• Manufacturer: Maxim Integrated Products

Specifications of DS1821S

• 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: Surface Mount
• Package / Case: 8-SOIC (5.3mm Width), 8-SOP, 8-SOEIAJ
• 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

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