DS1821
2 of 18
ORDER INFORMATION
ORDERING
NUMBER
PACKAGE
MARKING
DESCRIPTION
DS1821 DS1821 DS1821 in 3-pin PR35
DS1821+ DS1821 (See Note) DS1821 in 3-pin PR35
DS1821S DS1821S DS1821 in 208 mil 8-pin SO
DS1821S/T&R DS1821S DS1821 in 208 mil 8-pin SO, 2000 Piece Tape-and-Reel
DS1821S+ DS1821S (See Note) DS1821 in 208 mil 8-pin SO
DS1821S+T&R DS1821S (See Note) DS1821 in 208 mil 8-pin SO, 2000 Piece Tape-and-Reel
Note: A “+” symbol will also be marked on the package.
+ Denotes lead-free package.
DETAILED PIN DESCRIPTIONS Table 1
PR35 8-PIN
SO*
SYMBOL DESCRIPTION
1 2 GND
Ground pin.
2 1 DQ Open drain data input/output pin – 1-Wire operation; Open drain
thermostat output pin –thermostat operation.
3 8 V
DD
Power supply pin.
*All pins not specified in this table are “No Connect” pins.
OVERVIEW
Figure 1 shows a block diagram of the DS1821 and pin descriptions are given in Table 1. The DS1821
can operate as a standalone thermostat with user-programmable trip-points or as 8-bit temperature sensor
with a 1-Wire digital interface. The open-drain DQ pin functions as the thermostat output for thermostat
operation and as the data I/O pin for 1-Wire communications. The 1-Wire interface provides user access
to the nonvolatile (EEPROM) thermostat trip-point registers (T
H
and T
L
), the status/configuration register,
and the temperature register.
When configured as standalone thermostat, temperature conversions start immediately at power-up. In
this mode, the DQ pin becomes active when the temperature of the DS1821 exceeds the limit
programmed into the T
H
register, and remains active until the temperature drops below the limit
programmed into the T
L
register.
The DS1821 uses Dallas’ exclusive 1-Wire bus protocol that implements bus communication with one
control signal. This system is explained in detail in the 1-Wire BUS SYSTEM section of this datasheet.
