DS1775

3 of 14

DETAILED PIN DESCRIPTION Table 1

PIN

SYMBOL DESCRIPTION

PIN 1

SCL

Clock input/output pin for 2-wire serial communication port. This input

should be tied to GND for standalone thermostat operation.

PIN 2

GND

Ground pin.

PIN 3

O.S.

Thermostat output Open-drain output becomes active when temperature

state.

PIN 4

Supply Voltage 2.7V – 5.5V input power pin.

PIN 5

SDA

Data input/output pin for 2-wire serial communication port. In the standalone

thermostat mode, this input selects hysteresis.

OVERVIEW

A block diagram of the DS1775 is shown in Figure 1. The DS1775 consists of five major components:

1. Precision temperature sensor

2. Analog–to–digital converter

3. 2–wire interface electronics

4. Data registers

5. Thermostat comparator

The factory–calibrated temperature sensor requires no external components. Upon power–up, the DS1775

begins temperature conversions with the default resolution of 9 bits (0.5

°C resolution). The host can

periodically read the value in the temperature register, which contains the last completed conversion. As

conversions are performed in the background, reading the temperature register does not affect the

conversion in progress.

In power–sensitive applications the user can put the DS1775 into a shutdown mode, under which the

sensor will complete and store the conversion in progress and revert to a low–power standby state. In

applications where small incremental temperature changes are critical, the user can change the conversion

resolution from 9 bits to 10, 11, or 12. Each additional bit of resolution approximately doubles the

conversion time. This is accomplished by programming the configuration register. The configuration

register defines the conversion state, thermometer resolution/conversion time, active state of the

thermostat output, number of consecutive faults to trigger an alarm condition, and the method to

terminate an alarm condition.

temperature control, the comparator mode and the interrupt mode. This allows the user the flexibility to

customize the condition that would generate and clear a fault condition. Regardless of the mode chosen,

the O.S. output will become active only after the measured temperature exceeds the respective trippoint a

consecutive number of times; the number of consecutive conversions beyond the limit to generate an O.S.

is programmable. The power–up state of the DS1775 is in the comparator mode with a single fault

generating an active O.S.

Digital data is written to/read from the DS1775 via a 2–wire interface, and all communication is MSb

first.