Datasheet

DS1822
2 of 21
ORDER INFORMATION
ORDERING
NUMBER
PACKAGE
MARKING
DESCRIPTION
DS1822 1822 DS1822 in 3-pin TO92
DS1822/T&R 1822 DS1822 in 3-pin TO92, 2000 Piece Tape-and-Reel
DS1822+ 1822 (See Note) DS1822 in Lead-Free 3-pin TO92
DS1822+T&R 1822 (See Note) DS1822 in Lead-Free 3-pin TO92, 2000 Piece Tape-and-
Reel
DS1822Z DS1822 DS1822 in 150 mil 8-pin SO
DS1822Z/T&R DS1822 DS1822 in 150 mil 8-pin SO, 2500 Piece Tape-and-Reel
DS1822Z+ DS1822 (See Note) DS1822 in Lead-Free 150 mil 8-pin SO
DS1822Z+T&R DS1822 (See Note) DS1822 in Lead-Free 150 mil 8-pin SO, 2500 Piece
Tape-and-Reel
Note: A “+” symbol will also be marked on the package.
DETAILED PIN DESCRIPTIONS Table 1
8-PIN SO* TO-92 SYMBOL DESCRIPTION
5 1 GND
Ground.
4 2 DQ
Data Input/Output pin. Open-drain 1-Wire interface pin. Also
provides power to the device when used in parasite power mode
(see “Parasite Power” section).
3 3 V
DD
Optional V
DD
pin. V
DD
must be grounded for operation in
parasite power mode.
*All pins not specified in this table are “No Connect” pins.
OVERVIEW
Figure 1 shows a block diagram of the DS1822, and pin descriptions are given in Table 1. The 64-bit
ROM stores the device’s unique serial code. The scratchpad memory contains the 2-byte temperature
register that stores the digital output from the temperature sensor. In addition, the scratchpad provides
access to the 1-byte upper and lower alarm trigger registers (T
H
and T
L
), and the 1-byte configuration
register. The configuration register allows the user to set the resolution of the temperature-to-digital
conversion to 9, 10, 11, or 12 bits. The T
H
, T
L
and configuration registers are NV (EEPROM), so they will
retain data when the device is powered down.
The DS1822 uses Dallas’ exclusive 1-Wire bus protocol that implements bus communication using one
control signal. The control line requires a weak pullup resistor since all devices are linked to the bus via a
3-state or open-drain port (the DQ pin in the case of the DS1822). In this bus system, the microprocessor
(the master device) identifies and addresses devices on the bus using each device’s unique 64-bit code.
Because each device has a unique code, the number of devices that can be addressed on one bus is
virtually unlimited. The 1-Wire bus protocol, including detailed explanations of the commands and “time
slots,” is covered in the 1-WIRE BUS SYSTEM section of this data sheet.
Another feature of the DS1822 is the ability to operate without an external power supply. Power is instead
supplied through the 1-Wire pullup resistor via the DQ pin when the bus is high. The high bus signal also
charges an internal capacitor (C
PP
), which then supplies power to the device when the bus is low. This
method of deriving power from the 1-Wire bus is referred to as “parasite power.” As an alternative, the
DS1822 may also be powered by an external supply on V
DD
.