Datasheet ADT7301 (Analog Devices) - 9

ADT7301 THEORY OF OPERATION
The ADT7301 is a 13-bit digital temperature sensor with a 14th The ADT7301 can be placed into shutdown mode via the control bit that acts as a sign bit. The part houses an on-chip temperature register. This means that the on-chip oscillator is shut down and sensor, a 13-bit A/D converter, a reference circuit, and serial no further conversions are initiated until the ADT7301 is taken interface logic functions in SOT-23 and MSOP packages. The out of shutdown mode. The ADT7301 can be taken out of ADC section consists of a conventional successive approximation shutdown mode by writing al 0s into the control register. The converter based around a capacitor DAC. The parts run on a conversion result from the last conversion prior to shutdown 2.7 V to 5.25 V power supply. can stil be read from the ADT7301 even when it is in shutdown mode. The on-chip temperature sensor al ows an accurate measure- ment of the ambient device temperature to be made. The In normal conversion mode, the internal clock oscillator is reset specified measurement range of the ADT7301 is −40°C to after every read or write operation. This causes the device to start +150°C. Greater than 125°C, the ADT7301 is limited to 5% a temperature conversion, the result of which is typical y available of its 55°C operational lifetime. The structural integrity of the 1.2 ms later. Similarly, when the part is taken out of shutdown device may start to deteriorate when continuously operated at mode, the internal clock oscillator is started and a conversion is absolute maximum voltage and temperature specifications. initiated. The conversion result is available 1.2 ms later. Every result is stored in a buffer register and is loaded into the
CONVERTER DETAILS
temperature value register only at the first falling SCLK edge of The conversion clock for the part is internally generated. No every serial port activity. Serial port activity does not interfere external clock is required except when reading from and writing with conversion processes, and every conversion is completed, to the serial port. In normal mode, an internal clock oscillator even during a read operation. A conversion has to be completed runs an automatic conversion sequence. During this automatic before a read occurs, otherwise its result is not loaded into the conversion sequence, a conversion is initiated every 1.5 second. temperature value register and instead is loaded into the buffer At this time, the part powers up its analog circuitry and performs register. A new conversion is triggered at the end of each serial a temperature conversion. This temperature conversion typical y port activity, except when a conversion is already in progress. takes 1.2 ms, after which the analog circuitry of the part auto- matical y shuts down. The analog circuitry powers up again when the 1.5 second timer times out and the next conversion begins. Since the serial interface circuitry never shuts down, the result of the most recent temperature conversion is always available in the serial output register. Rev. B | Page 9 of 16 Document Outline Features Applications Functional Block Diagram General Description Product Highlights Revision History Specifications Timing Characteristics Absolute Maximum Ratings ESD Caution Pin Configurations and Function Descriptions Typical Performance Characteristics Theory of Operation Converter Details Temperature Value Register Temperature Conversion Equations Serial Interface Read Operation Write Operation Applications Information Microprocessor Interfacing ADT7301-to-MC68HC11 Interface ADT7301-to-8051 Interface ADT7301-to-PIC16C6x/7x Interface ADT7301-to-ADSP-21xx Interface Mounting the ADT7301 Supply Decoupling Outline Dimensions Ordering Guide