acquisitionZONE Products for the week of November 25, 2002
Referred to as the TC77 and the TC72, the thermal sensors are able to read temperature without the need for any external components and communicate thermal data via 3- and 4-wire industry standard interfaces, respectively. The TC72, offered in the 8-pin 3x3-mm DFN and the MSOP package, and the TC77, offered in the tiny 5-pin SOT-23 and the 8-pin SOIC package, enable designers to save a significant amount of board space while improving temperature sensing capability. The DFN package has a lower profile, as well as significantly better thermal resistance than standard package types and also provides designers improved ability to manufacture through the elimination of conventional side leads.
"These new devices offer exceptional power savings while occupying the smallest possible board space. In addition, they are capable of measuring temperature extremely accurately, with a maximum temperature error of 1 degree Celsius over a certain temperature range, and communicate with a variety of microcontrollers and other digital ICs," said George Paparrizos, product marketing manager for the Analog and Interface Product Division at Microchip. "Microchip continues to design and develop proprietary solutions that enable designers to solve most temperature-sensitive requirements."
Both sensors consume the lowest operating current (250uA typical) for a given temperature conversion time in the industry. This combined with the ultra-low power shutdown mode (1 microamp typical), enables designers to extend battery life in portable electronics.
The TC72 is capable of reading temperatures from -55°C to +125°C
and features an operating voltage range of 2.65- to 5.5-volts. Temperature
resolution for this device is 0.25°C per bit and temperature accuracy
is 2°C maximum over the entire -40°C to +85°C temperature range.
The TC77 offers very high-resolution (0.0625°C per bit) enabling systems
to quickly detect critical thermal conditions, which leads to precise temperature
measurement. The device offers an extended temperature range of -55°C
to +125°C and an operating voltage range of 2.7- to 5.5-volts.
analogZONE Says . . .
These two parts are very alike, but rather different. Both the TC72 and TC77 are self-contained temperature sensors with a diode sensor on-chip. The TC72 uses a 10-bit ADC - giving a resolution of 0.25°C per bit - while the TC77 uses a 13-bit ADC, giving it a resolution of 0.0625°C per bit and allowing for possibly very accurate calibrations beyond the simple accuracy of the device itself.
In parts like this it is extremely important that the self-heating is carefully controlled by very low dissipation: Both parts achieve this with 250 µA typical consumption during conversions, while the TC72 has a typical shutdown consumption of 1 µA, and the TC77 of 0.1 µA.
Another major difference between the two parts is the ideal operating supply. The range for both is about 2.7 V to 5.5 V, but the ideal operating point for the devices is specified by selected parts for 2.8 V, 3.3 V and 5.0 V in the TC72, and for either 3.3 V or 5.0 V for the TC77. The maximum clock frequency for the TC72 is 7.5 MHz and for the TC77 it is 7.0 MHz. The interface for both is SPI compatible and the format of the temperature information is in a two's complement word.
The TC72 will find sockets in general temperature sensing applications where a couple of degrees is unimportant and the user does not want to program difficult hysteresis into control systems - that would include disk drives, entertainment equipment, consumer products, etc. The TC77 is more likely to find sockets in equipment where "close-to-destruction" temperatures are preferred to maximize performance - that would include PC card devices, high-end hard drives and the like. The high resolution of the TC77 also makes it an ideal candidate for industrial thermal control systems and as a direct - simpler for most designers - substitute for thermistors.
A very nice pair of products although I find the choice of packages unusual. Both the TC72 and TC77 are in production with the TC72 available in MSOP-8 and DFN-8, priced at $0.79 and $0.89, respectively, in 1000-piece lots. The TC77 is available in SOIC-8 and SOT-23-5, priced at $0.79 and $0.86, respectively, also in 1000-piece lots.
Data Sheet (TC72)
Data Sheet (TC77)