DS1721

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DETAILED PIN DESCRIPTION Table 1

PIN

SYMBOL

DESCRIPTION

1SDA

Data input/output pin. For 2-wire serial communication port.

2SCL

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

Thermostat output. Active when temperature exceeds TH; will reset when

temperature falls below TL.

4

GND

Ground pin.

5A2

Address input pin.

6A1

Address input pin.

7A0

Address input pin.

Supply Voltage. 2.7V to 5.5V input power pin.

OVERVIEW

A block diagram of the DS1721 is shown in Figure 1.

The DS1721 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 DS1721

is in an idle mode. Upon issuance of a Start Convert T command [51h], the DS1721 begins temperature

conversions with the default resolution of 12 bits (0.0625°C resolution). Following an 8-bit command

protocol, temperature data can be read over the 2-wire interface. 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 DS1721 in a “one-shot” mode, under which the

sensor will complete and store one temperature conversion and return to a low-power standby state. In

time-sensitive applications, the user can change the conversion resolution from 12 bits to 9, 10, or 11.

Each additional bit of resolution approximately doubles the conversion time, so 9-bit conversions can be

performed in less than a quarter of a second.

This is accomplished by issuing a command protocol to the configuration register. It is recommended that

the user issue the command protocol to program the configuration register before any temperature

conversion commands are issued after power-up. This is due to the fact that the configuration data is

stored in volatile memory and will always power-up in the default state. The configuration register

defines the conversion mode, thermometer resolution/conversion time, and active state of the thermostat

comparator output. It also contains 3 status bits denoting the state of temperature conversions and

thermostat flags.

The user can also program over-temperature (TH) and under-temperature (TL) setpoints for thermostatic

operation. The power-up state of TH is 80°C and that for TL is 75°C. The result of each temperature

measured temperature exceeds the programmed TH, and remains latched in the active state until