acquisitionZONE Products for the week of September 1, 2003
Analog Devices has expanded its industry-leading portfolio of temperature sensors with the addition of the ADT7301, the most accurate SPI-compatible temperature sensor available in a tiny SOT (small outline transistor) package.
The ADT7301 13-bit temperature-to-digital converter provides +/- 0.5 degrees C measurement accuracy from 0 to 70 degrees C, and is fully specified for operation from -40 to +150 degrees C. In addition to its small footprint, the device's low shutdown current (1 microamp) and wide supply range (2.7 V to 5.5 V) make it ideal for many low-power applications requiring precise thermal measurement.
The ADT7301 contains a flexible serial interface, which allows easy interfacing
to most microcontrollers. The part is compatible with SPI, QSPI, and MICROWIRE
protocols, as well as DPSs (digital signal processors). The ADT7301 also
offers a standby mode for additional power savings.
analogZONE Says . . .
There are 0.5% accurate digital temperature sensors out there, and they are available in SOT-23 but as far as I know there are no other true 13-bit parts and none with the kind of flexibility provided here for the interface.
Other "13-bit" parts are actually 12 bits plus sign and their resolution is 0.0625°C; with this true 13-bit part (with a 14th bit as sign) that resolution is improved to 0.03125°C while the four wire interface allows connections to QSPI, SPI, Microwire, or directly to a DSP. Those four wires plus the supply and ground just squeeze into a SOT-23-6. Also, other 0.5% accurate sensors seem to have an upper operating temperature range of about +125°C, while the ADT7301 makes it up to +150°C (limited to 5% of its +55°C time.)
There are two versions of the part, a -3.3 and a -5, which are optimized for 3.3-V and 5.0-V supplies, respectively, although both parts can be used anywhere over the supply range of 2.7 V to 5.5 V. Typical converting current supplies are 1.6 mA with the shutdowns of less than 400 µA. The normal auto conversion update rate for temperature measurements is every second with a conversion time of typically 208 µs.
The ±0.5% maximum accuracy is over the range of 0°C to +70°C. Extending the range down to -40°C and up to +85°C reduces the accuracy to a maximum ±1%, and out to +125°C it is ±2%, and to the maximum +150°C it is ±3%.
The architecture is a bandgap temperature sensor with a 14-bit SAR ADC (13 bits for temperature value) driving a 14-bit read-only register of temperature values, and sign, loaded through the serial interface. The reference is on-chip, of course, as is the conversion clock which can be turned off over the serial bus for shutdown. Shutdown also occurs between conversions. The sign bit is the MSB while the other 13 bits are in twos complement format.
The accuracy, the resolution, simplicity, low power and the ability to connect the part directly to a DSP are going to dramatically enhance the position of the product in the marketplace. Analog Devices is looking for about 30 cents in premium for the part and it may land that in low volume applications. The markets are extensive and cover everything from PCs to medical equipment and include process control, appliances, office equipment and portable products.
The ADT7301 is sampling in SOT-23-6 and MSOP-8 and will be in production in October 2003 (at least I hope the 2004 date in the press release is a typo!) It will be priced at $1.20 in 1000-piece lots.