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ADT6501ARJP105 Datasheet(PDF) 8 Page - Analog Devices |
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ADT6501ARJP105 Datasheet(HTML) 8 Page - Analog Devices |
8 / 16 page Preliminary Technical Data ADT6501/ADT6502/ADT6503/ADT6504 Rev. PrA | Page 8 of 16 THEORY OF OPERATION CIRCUIT INFORMATION The ADT6501/ADT6502/ADT6503/ADT6504 are 12-bit digital temperature sensors with the 12th bit acting as the sign bit. An on- board temperature sensor generates a voltage precisely proportional to absolute temperature that is compared to an internal voltage reference and input to a precision digital modulator. The 12-bit output from the modulator is input into a digital comparator where it is compared with a factory set trip level. The output trip pin is activated if the temperature measured is greater than the factory set trip level. Overall accuracy for the ADT650x family is ±6°C from −45°C to +115°C. The on-board temperature sensor has excellent accuracy and linearity over the entire rated temperature range without needing correction or calibration by the user. The ADT6501/ADT6503 have active-low, open-drain output structures that can only sink current. The ADT6502/ADT6504 have active-high, push-pull output structures that can sink and source current. On power-up, the output cannot become active until the first conversion is completed. This typically takes 30 ms. The sensor output is digitized by a first-order, ∑-Δ modulator, also known as the charge balance type analog-to-digital converter (ADC). This type of converter utilizes time-domain oversampling and a high accuracy comparator to deliver 12 bits of effective accuracy in an extremely compact circuit. CONVERTER DETAILS The ∑-Δ modulator consists of an input sampler, a summing network, an integrator, a comparator, and a 1-bit digital-to- analog converter (DAC). Similar to the voltage-to-frequency converter, 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 is called oversampling. Oversampling spreads the quantization noise over a much wider band than that of the input signal, improving overall noise performance and increasing accuracy. Σ-Δ MODULATOR INTEGRATOR COMPARATOR 1-BIT DAC LPF DIGITAL FILTER CLOCK GENERATOR VOLTAGE REF AND VPTAT TEMPERATURE VALUE REGISTER 1-BIT 12-BIT + – Figure 14. First-Order ∑-Δ Modulator The modulated output of the comparator is encoded using a circuit technique that results in SMBus/I2C temperature data. FACTORY PROGRAMMED THRESHOLD RANGE The ADT6501/ADT6502/ADT6503/ADT6504 are available with factory set threshold levels ranging from −45°C to +115°C in 10°C. The ADT6501/ADT6503 outputs are intended to interface to reset inputs of microprocessors. The ADT6502/ADT6504 are intended for driving circuits of applications, such as fan control circuits. Table 4 lists the available temperature threshold ranges. Table 4. Factory Set Temperature Threshold Ranges Device Threshold (TTH) Range ADT6501 +35°C < TTH < +115°C ADT6502 +35°C < TTH < +115°C ADT6503 −45°C < TTH < +15°C ADT6504 −45°C < TTH < +15°C HYSTERESIS INPUT The HYST pin is used to select a temperature hysteresis of 2°C or 10°C. If the HYST pin is connected to VCC then a hysteresis of 10°C is selected or if the HYST pin is connected to GND then a hysteresis of 2°C is selected. The HYST pin should not be left floating. Hysteresis prevents oscillation on the output pin when the temperature is approaching the trip point, after it activates. For example, if the temperature trip is 45°C and the hysteresis selected is 10°C, the temperature would have to go as low as 35°C before the output deactivates. |
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