The DS1631 , DS1631A, and DS1731 digital thermometers provide 9-, 10-, 11-, or 12-digit temperature readings over the entire -55°C to + 125 °C range. The DS1631 and DS1631A thermometers have an accuracy of ±0.5°C over the 0°C to +70°C range with a power supply of 3.0V ≤ VDD ≤ 5.5V. The DS1731, on the other hand, has ±1°C accuracy over the -10°C to +85°C range with 3.0V ≤ VDD ≤ 5.5V supply conditions. The thermostats for the three devices provide custom temperature hysteresis with user-defined thresholds (TH and TL). TH and TL registers and thermometer configuration settings are stored in NV EEPROM, so they can be programmed prior to installation. In addition, the DS1631A automatically starts temperature measurements on power-up, allowing it to be used as a monolithic thermostat. Communication with the DS1631/DS1631A/DS1731 is accomplished through a 2-wire serial port, and the three address pins allow up to 8 devices to be attached to the same 2-wire bus.

Operating temperature measurement

Bandgap-based temperature sensors for the DS1631, DS1631A, and DS1731 to measure temperature. A delta-sigma analog-to-digital converter (ADC) converts the measured temperature to a 9-, 10-, 11-, or 12-bit (user-selectable) digital value that is calibrated in °C; for °F applications A lookup table or conversion program must be used. Throughout this specification, the term "conversion" is used to refer to the entire sequence of temperature measurements and ADCs. The DS1631 and DS1731 are always powered in a low-power idle state, and the Start Conversion T command must be used to initiate a conversion. The DS1631A automatically starts converting to power mode determined by the 1SHOT bit of the configuration register. The DS1631, DS1631A, and DS1731 can be programmed to perform continuous continuous conversions (continuous conversion mode), or to perform single conversions on command (single-shot mode). The conversion mode is programmed through the 1SHOT bit in the configuration register as described in the Configuration Register section of this data sheet. In continuous conversion mode, the DS1631A starts continuous conversion immediately after power-up, and after the DS1631 and DS1731 start to issue the start conversion T command, continuous conversion. For all three devices, continuous conversion continues until a Stop Conversion T command is issued, at which point the device enters a low power idle state. Continuous conversions can be restarted at any time using the Start Conversion T command. In single-shot mode, the DS1631A performs a single-shot conversion on power-up, while the DS1631 and DS1731 perform a single-temperature conversion when the Start Conversion T command is issued. For all three devices, when the conversion is complete, the device enters a low-power standby state and remains in that state until a temperature conversion is initiated again by a Start Conversion T command. The resolution of the output digital temperature data is user-configurable in 9, 10, 11, or 12 bits, corresponding to 0.5°C, 0.25°C, 0.125°C, and 0.0625°C temperature increments, respectively. The default resolution at power-up is 12 bits, and it can be changed by bits in the R0 and R1 configuration registers. Note that the conversion time is doubled for each additional bit of resolution. After each conversion, the digital temperature is stored as a dual 16-bit two's complement number as shown in Figure 1. The flag (S) byte of the temperature register indicates if the temperature is positive or negative: positive S=0 and negative S=1 , the read temperature command provides user access to the temperature register. Bits 3 to 0 of the temperature register are hardwired to 0. When the device is configured for 12-bit resolution, the upper 12 bits (bits 15 to 4) of the temperature register contain temperature data. For 11-bit resolution, the 11-bit MSB (bits 15 to 5) of the temperature register contains data, and bit 4 is 0. Likewise, for 10-bit resolution, the 10-bit MSB (bits 15 to 6) contains data, and the 9-bit MSB (bits 15 to 7) of 9 contains data, and all unused low-order bits contain 0. The table below gives examples of output data with 12-bit resolution and the corresponding temperature.

figure 1

Table 1 Resolution Temperature/Data Relationship

Key Features

The DS1631 and DS1631A provide ±0.5°C accuracy over the 0°C to +70°C range

The DS1731 provides ±1°C accuracy over the -10°C to +85°C range

DS1631A automatically starts temperature measurement at power-up

Operating Temperature Range: -55°C to +125°C (-67°F to + 257 °F)

Temperature measurement without external components

User selectable 9, 10, 11 or 12 bit output resolution

Wide supply range (+2.7V to +5.5V)

750ms (max) temperature to digital time

Multi-node capability simplifies distributed temperature measurement applications

Thermostat setpoints are user-defined and non-volatile (NV)

Read/write data via a 2-wire serial port (SDA and SCL pins)

All three devices are available in an 8-pin μSOP package, while the DS1631 is also available in a 150mil, SO package

Functional block diagram: