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

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

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

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.