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ADT7320 Datasheet(PDF) 10 Page - Analog Devices |
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ADT7320 Datasheet(HTML) 10 Page - Analog Devices |
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10 / 25 page  Data Sheet ADT7320 Rev. 0 | Page 9 of 24 THEORY OF OPERATION CIRCUIT INFORMATION The ADT7320 is a high accuracy digital temperature sensor that uses a 16-bit ADC to monitor and digitize the temperature to a resolution of 0.0078°C. By default, the ADC resolution is set to 13 bits (0.0625°C). An internal temperature sensor generates a voltage proportional to absolute temperature; this voltage is compared to an internal voltage reference and input into a precision digital modulator. The internal temperature sensor has high accuracy and linearity over the entire rated temperature range without the need for correction or calibration by the user. The sensor output is digitized by a sigma-delta (Σ-Δ) modulator, also known as the charge balance type ADC. This type of converter uses time domain oversampling and a high accuracy comparator to deliver 16 bits of resolution in an extremely compact circuit. CONVERTER DETAILS The Σ-Δ modulator consists of an input sampler, a summing network, an integrator, a comparator, and a 1-bit digital-to-analog converter (DAC). This architecture creates a negative feedback loop and minimizes the integrator output by changing the duty cycle of the comparator output in response to the input voltage changes. The comparator samples the output of the integrator at a much higher rate than the input sampling frequency. This oversampling spreads the quantization noise over a much wider band than that of the input signal, improving overall noise performance and increasing accuracy. The modulated output of the comparator is encoded using a circuit technique that results in SPI temperature data. Σ-∆ MODULATOR INTEGRATOR COMPARATOR TEMPERATURE VALUE REGISTER CLOCK GENERATOR LPF DIGITAL FILTER 1-BIT DAC VOLTAGE REFERENCE 1-BIT 13-/16-BIT Figure 11. Σ-∆ Modulator The ADT7320 can be configured to operate in any one of the following four operating modes: normal mode, one-shot mode, 1 SPS mode, and shutdown mode. CONTINUOUS CONVERSION MODE In continuous conversion mode (default power-up mode), the ADT7320 runs an automatic conversion sequence. During this automatic conversion sequence, a conversion takes 240 ms to complete and the ADT7320 is continuously converting. This means that as soon as one temperature conversion is completed, another temperature conversion begins. Each temperature conversion result is stored in the temperature value register and is available through the SPI interface. In continuous conversion mode, the read operation provides the most recent converted result. On power-up, the first conversion is a fast conversion, taking typically 6 ms. If the temperature exceeds 147°C, the CT pin is asserted low. If the temperature exceeds 64°C, the INT pin is asserted low. Fast conversion temperature accuracy is typically within ±5°C. The conversion clock for the part is generated internally. No external clock is required except when reading from and writing to the serial port. The measured temperature value is compared with a critical temperature limit (stored in the 16-bit TCRIT setpoint register), a high temperature limit (stored in the 16-bit THIGH setpoint register), and a low temperature limit (stored in the 16-bit TLOW setpoint register). If the measured value exceeds the high or low temperature limits, the INT pin is activated; if it exceeds the TCRIT limit, the CT pin is activated. The polarity of the INT and CT pins is programmable for via the configuration register, and the INT and CT pins are also programmable for interrupt mode via the configuration register. |
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