Maxim's press release covers the Dallas Semiconductor DS1626 thermometer chip, but there's also a Type DS1726 counterpart that's not mentioned. While both surface-mount ICs permit temperature measurement and thermostat operation over a wide -55° C to +125° C MIL temperature range, the DS1726 is for applications where ±1° C accuracy from -10° C to +85° C is sufficient.
Like the DS1626, resolution of measured temperature is user-selectable from 9 bits to 12 bits. Both ICs can convert temperature readings with 12-bit resolution in 750 ms max. (a 9-bit conversion can occur in about 94 ms). Both devices pack nonvolatile EEPROM arrays.
As you can see from the block diagram, these devices give you thermostatic output signals on three dedicated lines. Two more output lines handle over- and under-temperature signaling.
click for full-size schematic
For stand-alone thermostat operation, the over- and under-temperature settings can also be pre-programmed, with values stored in EEPROM.
What's not said in Maxim's press statement is that these chips rely on internal bandgap-based sensors. Also, they include sigma-delta analog-to-digital converter blocks that convert measured temperature to values pre-calibrated in degrees C. If you want to use them for Fahrenheit applications, a lookup table will be required, or a conversion routine has to be run on an associated microprocessor or controller.
Both ICs can also be configured to make either continuous temperature measurements, or make single measurements on command in a so-called one-shot mode. What mode you prefer is selected by setting a bit in a configuration register. This bit is also stored in the EEPROM array, permitting pre-set programming prior to installation on a circuit board.
In Continuous mode, a Start Convert command is issued and the chip makes consecutive temperature measurements until it receives a Stop command. In the one-shot mode, the Start Convert command causes a single measurement to be taken, and then the chip returns to its power-down idle state.
As I indicated above, the resolution of either device is user-configurable to 9 bits, 10 bits, 11 bits, or 12 bits, corresponding to temperature increments of 0.5° C, 0.25° C, 0.125° C, and 0.0625° C, respectively. The resolution is set in a configuration register, and settings are stored in EEPROM.
When setting up one of these devices, a tradeoff is that conversion time doubles for each additional bit of resolution, as I noted earlier. However, most temperature measuring applications don't require great speed anyway, so these time-vs-resolution tradeoffs probably won't be too significant in typical applications. However, the thermal mass of these packages is quite small, so reasonably rapid changes in temperature should be quite trackable.
In Thermostat mode, updates occur after every temperature conversion. The device then sits there delivering its updated value until the next conversion completes a cycle. The chip's output lines are asserted when a measured temperature is higher than, or equal to, a value stored in the chip's register.
Similarly, a low is asserted on an output pin if the temperature being measured is equal to, or falls below, a value you preset in the IC's Low register. Having two lines is what gives you programmable hysteresis.
In their stand-alone thermostat modes, the thermostat function can be used without a microcontroller in Start/Stop temperature conversions. Like other functions, a CPU bit in a configuration register determines if the stand-alone mode is enabled or not.
When you consider the low price tags of these sensor/converter chips, it's remarkable that so much accuracy and function can be had for so little. Moreover, these chips require no external resistors or capacitors for typical operation. Both sensors are mute testimony to the state of the art in low cost solid-state sensor and measurement technology.