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ADT7420UCPZ Datasheet(PDF) 9 Page - Analog Devices |
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ADT7420UCPZ Datasheet(HTML) 9 Page - Analog Devices |
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9 / 24 page  Preliminary Technical Data ADT7420 Rev. PrA | Page 9 of 24 THEORY OF OPERATION CIRCUIT INFORMATION The ADT7420 is a 13-bit digital temperature sensor that is extend- able to 16 bits for greater resolution. An on-board temperature sensor generates a voltage proportional to absolute temperature, which is compared to an internal voltage reference and input to a precision digital modulator. The on-board temperature sensor has high accuracy and linearity over the entire rated temperature range without needing 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 analog-to-digital conver- ter. This type of converter utilizes time-domain oversampling and a high accuracy comparator to deliver 16 bits of resolution in an extremely compact circuit. Configuration register functions consist of Switching between 13-bit and 16-bit resolution Switching between normal operation and full power-down Switching between comparator and interrupt event modes on the INT and CT pins Setting the active polarity of the CT and INT pins Setting the number of faults that activate CT and INT Enabling the standard one-shot mode and 1 SPS mode CONVERTER DETAILS The Σ-Δ modulator consists of an input sampler, a summing network, an integrator, a comparator, and a 1-bit 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 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 I2C temperature data. Σ-∆ MODULATOR INTEGRATOR COMPARATOR TEMPERATURE VALUE REGISTER CLOCK GENERATOR LPF DIGITAL FILTER 1-BIT DAC VOLTAGE REF AND VPTAT 1-BIT 13-BIT Figure 11. Σ-Δ Modulator TEMPERATURE MEASUREMENT In normal mode, the ADT7420 runs an automatic conversion sequence. During this automatic conversion sequence, a conver- sion takes 240 ms to complete and the ADT7420 is continuously converting. This means that as soon as one temperature conver- sion is completed, another temperature conversion begins. Each temperature conversion result is stored in the temperature value registers and is available through the I2C 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 asserts low. If the temperature exceeds 64°C, the INT pin asserts 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 read/write register), a high temperature limit (stored in the 16-bit THIGH set- point read/write register), and a low temperature limit (stored in the 16-bit TLOW setpoint read/write register). If the measured value exceeds these limits, the INT pin is activated; and if it exceeds the TCRIT limit, the CT pin is activated. The INT and CT pins are programmable for polarity via the configuration register, and the INT and CT pins are also programmable for interrupt mode via the configuration register. ONE-SHOT MODE Setting Bit 5 to 0 and Bit 6 to 1 of the configuration register (Register Address 0x03) enables the one-shot mode. When this mode is enabled, the ADT7420 immediately completes a conversion and then goes into shutdown mode. Wait for a minimum of 240 ms after writing to the operation mode bits to the one-shot bits before reading back the temperature from the temperature value register. This time ensures that the ADT7420 has time to power up and complete a conversion. The one-shot mode is useful when one of the circuit design priorities is to reduce power consumption. 1 SPS MODE In this mode, the part performs one measurement per second. A conversion takes only 60 ms, and it remains in the idle state for the remaining 940 ms period. This mode is enabled by writing 1 to Bit 5 and 0 to Bit 6 of the configuration register (Register Address 0x03). |
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