Datasheet ADT7302 (Analog Devices) - 9

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ADT7302 THEORY OF OPERATION
The ADT7302 is a 13-bit digital temperature sensor with a 14th later, typically. Every result is stored in a buffer register and is bit that acts as a sign bit. The part houses an on-chip temperature only loaded into the temperature value register at the first sensor, a 13-bit ADC, a reference circuit, and serial interface falling SCLK edge of every serial port activity. Serial port logic functions in SOT-23 and MSOP packages. The ADC activity does not interfere with the conversion process and section consists of a conventional successive approximation every conversion completes its process even during a read converter based around a capacitor DAC. The parts can run on operation. A conversion has to be completed before a read a 2.7 V to 5.25 V power supply. occurs, otherwise its result does not get loaded into the temperature value register and instead goes into the buffer The on-chip temperature sensor al ows an accurate measurement register. A new conversion is triggered at the end of each serial of the ambient device temperature to be made. The specified port activity except when a conversion is already in progress. measurement range of the ADT7302 is −40°C to +125°C. The structural integrity of the device can start to deteriorate when
TEMPERATURE VALUE REGISTER
continuously operated at absolute maximum voltage and The temperature value register is a 14-bit read-only register that temperature specifications. stores the temperature reading from the ADC in 13-bit twos
CONVERTER DETAILS
complement format plus a sign bit. The MSB (DB13) is the sign bit. The ADC can theoretically measure a 255°C temperature The conversion clock for the part is internally generated. No span. The internal temperature sensor is guaranteed to a low external clock is required except when reading from and writing value limit of −40°C and a high limit of +125°C. The temperature to the serial port. In normal mode, an internal clock oscillator data format is shown in Table 5, which also shows the runs an automatic conversion sequence. During this automatic temperature measurement range of the device (−40°C to conversion sequence, a conversion is initiated every 1.5 second. +125°C). A typical performance curve is shown in Figure 11. At this time, the part powers up its analog circuitry and performs a temperature conversion. This temperature conversion typical y
Table 5. Temperature Data Format
takes 1.2 ms, after which the analog circuitry of the part auto-
Temperature Digital Output DB13…DB0
matical y shuts down. The analog circuitry powers up again when −40°C 11, 1011 0000 0000 the 1.5 second timer times out and the next conversion begins. −30°C 11, 1100 0100 0000 Since the serial interface circuitry never shuts down, the result −25°C 11, 1100 1110 0000 of the most recent temperature conversion is always available in −10°C 11, 1110 1100 0000 the serial output register. −0.03125°C 11, 1111 1111 1111 0°C 00, 0000 0000 0000 The ADT7302 can be placed into shutdown mode via the +0.03125°C 00, 0000 0000 0001 control register. This means that the on-chip oscillator is +10°C 00, 0001 0100 0000 shut down and no further conversions are initiated until the +25°C 00, 0011 0010 0000 ADT7302 is taken out of shutdown mode. The ADT7302 can +50°C 00, 0110 0100 0000 be taken out of shutdown mode by writing al zeros into the +75°C 00, 1001 0110 0000 control register. The conversion result from the last conversion +100°C 00, 1100 1000 0000 prior to shutdown can stil be read from the ADT7302 even +125°C 00, 1111 1010 0000 when it is in shutdown mode. In normal conversion mode, the internal clock oscillator is reset
Temperature Conversion Equations
after every read or write operation. This causes the device to Positive Temperature = ADC Code(d)/32 start a temperature conversion, the result of which is typical y Negative Temperature = (ADC Code(d)1 − 16384)/32 available 1.2 ms later. Similarly, when the part is taken out of Negative Temperature = (ADC Code(d)2 − 8192)/32 shutdown mode, the internal clock oscil ator is started and a conversion is initiated. The conversion result is available 1.2 ms 1 ADC Code uses all 14 bits of the data byte, including the sign bit. 2 DB13 (the sign bit) is removed from the ADC code. 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 ADT7302 to MC68HC11 Interface ADT7302 to 8051 Interface ADT7302 to PIC16C6x/7x and PIC16F873 Interface ADT7302 to ADSP-21xx Interface Mounting the ADT7302 Supply Decoupling Outline Dimensions Ordering Guide