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ADT7302ARTZ-REEL Arkusz danych(PDF) 8 Page - Analog Devices |
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ADT7302ARTZ-REEL Arkusz danych(HTML) 8 Page - Analog Devices |
8 / 14 page ADT7302 Preliminary Technical Data Rev. PrE | Page 8 of 14 CIRCUIT INFORMATION The ADT7302 is a 13-bit digital temperature sensor with a 14 th bit that acts as a sign bit. The part houses an on-chip tempera- ture sensor, a 13-bit A/D converter, a reference circuit, and serial interface logic functions in SOT-23 and MSOP packages. The A/D converter section consists of a conventional successive-approximation converter based around a capacitor DAC. The parts are capable of running on a 2.7 V to 5.5 V power supply. The on-chip temperature sensor allows an accurate measure- ment of the ambient device temperature to be made. The specified measurement range of the ADT7302 is −40°C to +125°C. The structural integrity of the device starts to deteriorate when operated at voltage and temperature maximum specifications. CONVERTER DETAILS The conversion clock for the part is internally generated; no external clock is required except when reading from and writing to the serial port. In normal mode, an internal clock oscillator runs an automatic conversion sequence. During this automatic conversion sequence, a conversion is initiated every 1 second. At this time, the part powers up its analog circuitry and performs a temperature conversion. This temperature conversion typically takes 800 µs, after which time the analog circuitry of the part automatically shuts down. The analog circuitry powers up again when the 1 second timer times out and the next conversion begins. The result of the most recent temperature conversion is always available in the serial output register because the serial interface circuitry never shuts down. The ADT7302 can be placed in a shutdown mode via the con- trol register, in which case the on-chip oscillator is shut down and no further conversions are initiated until the ADT7302 is taken out of shutdown mode. The ADT7302 can be taken out of shutdown mode by writing all zeros into the control register. The conversion result from the last conversion prior to shut- down can still be read from the ADT7302 even when it is in shutdown mode. In normal conversion mode, the internal clock oscillator is reset after every read or write operation. This causes the device to start a temperature conversion, the result of which is typically available 800 µs later. Similarly, when the part is taken out of shutdown mode, the internal clock oscillator is started and a conversion is initiated. The conversion result is available 800 µs later, typically. Reading from the device before a conversion is complete causes the ADT7302 to stop converting; the part starts again when serial communication is finished. This read operation provides the previous result. TEMPERATURE VALUE REGISTER The temperature value register is a 14-bit read-only register that stores the temperature reading from the ADC in 13-bit twos complement format plus a sign bit. The MSB (DB13) is the sign bit. The ADC can theoretically measure a 255°C temperature span. The internal temperature sensor is guaranteed to a low value limit of –40°C and a high limit of +125°C. The temperature data format is shown in Table 5, which shows the temperature measurement range of the device (–40°C to +125°C). A typical performance curve is shown in Figure 6. Table 5. Temperature Data Format Temperature Digital Output DB13…DB0 −40°C 11, 1011 0000 0000 −30°C 11, 1100 0100 0000 −25°C 11, 1100 1110 0000 −10°C 11, 1110 1100 0000 −0.03125°C 11, 1111 1111 1111 0°C 00, 0000 0000 0000 +0.03125°C 00, 0000 0000 0001 +10°C 00, 0001 0100 0000 +25°C 00, 0011 0010 0000 +50°C 00, 0110 0100 0000 +75°C 00, 1001 0110 0000 +100°C 00, 1100 1000 0000 +125°C 00, 1111 1010 0000 Temperature Conversion Formula 1. Positive Temperature = ADC Code(d)/32 2. Negative Temperature = (ADC Code*(d) – 16384)/32 *Using all 14 bits of the data byte, includes the sign bit. Negative Temperature = (ADC Code(d)* – 8192)/32 *DB13 (sign bit) is removed from the ADC code –40°C –0.03125 °C –30°C 11, 1111, 1111, 1111 11, 1100, 0100, 0000 11, 1011, 0000, 0000 TEMPERATURE (°C) 75°C 125°C 01, 0010, 1100, 0000 00, 1001, 0110, 0000 00, 0000, 0000, 0001 Figure 12. Temperature to Digital Transfer Function |
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