Datasheet ADT7320 (Analog Devices) - 9

Data Sheet ADT7320 THEORY OF OPERATION CIRCUIT INFORMATION
The ADT7320 can be configured to operate in any one of the The ADT7320 is a high accuracy digital temperature sensor that following four operating modes: normal mode, one-shot mode, uses a 16-bit ADC to monitor and digitize the temperature to a 1 SPS mode, and shutdown mode. resolution of 0.0078°C. By default, the ADC resolution is set to
CONTINUOUS CONVERSION MODE
13 bits (0.0625°C). An internal temperature sensor generates a voltage proportional to absolute temperature; this voltage is In continuous conversion mode (default power-up mode), the compared to an internal voltage reference and input into a ADT7320 runs an automatic conversion sequence. During this precision digital modulator. automatic conversion sequence, a conversion takes 240 ms to complete and the ADT7320 is continuously converting. This means The internal temperature sensor has high accuracy and linearity that as soon as one temperature conversion is completed, another over the entire rated temperature range without the need for temperature conversion begins. Each temperature conversion correction or calibration by the user. result is stored in the temperature value register and is available through the SPI interface. In continuous conversion mode, the The sensor output is digitized by a sigma-delta (Σ-Δ) modulator, read operation provides the most recent converted result. also known as the charge balance type ADC. This type of converter uses time domain oversampling and a high accuracy comparator to On power-up, the first conversion is a fast conversion, taking deliver 16 bits of resolution in an extremely compact circuit. 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
CONVERTER DETAILS
asserted low. Fast conversion temperature accuracy is typically The Σ-Δ modulator consists of an input sampler, a summing within ±5°C. network, an integrator, a comparator, and a 1-bit digital-to-analog converter (DAC). This architecture creates a negative feedback The conversion clock for the part is generated internally. No loop and minimizes the integrator output by changing the duty external clock is required except when reading from and writing cycle of the comparator output in response to the input voltage to the serial port. changes. The comparator samples the output of the integrator at The measured temperature value is compared with a critical a much higher rate than the input sampling frequency. This temperature limit (stored in the 16-bit TCRIT setpoint register), a oversampling spreads the quantization noise over a much wider high temperature limit (stored in the 16-bit THIGH setpoint band than that of the input signal, improving overall noise register), and a low temperature limit (stored in the 16-bit TLOW performance and increasing accuracy. setpoint register). If the measured value exceeds the high or low The modulated output of the comparator is encoded using a temperature limits, the INT pin is activated; if it exceeds the TCRIT circuit technique that results in SPI temperature data. limit, the CT pin is activated. The polarity of the INT and CT pins is programmable for via the configuration register, and the
Σ-∆ MODULATOR
INT and CT pins are also programmable for interrupt mode via
INTEGRATOR
the configuration register.
COMPARATOR VOLTAGE REFERENCE 1-BIT DAC 1-BIT TEMPERATURE CLOCK LPF DIGITAL VALUE
2
GENERATOR FILTER
01
REGISTER
2-
13-/16-BIT
01 09 Figure 11. Σ-∆ Modulator Rev. 0 | Page 9 of 24 Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION PRODUCT HIGHLIGHTS FUNCTIONAL BLOCK DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS SPI TIMING SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION CIRCUIT INFORMATION CONVERTER DETAILS CONTINUOUS CONVERSION MODE ONE-SHOT MODE CT and INT Operation in One-Shot Mode 1 SPS MODE SHUTDOWN MODE FAULT QUEUE TEMPERATURE DATA FORMAT TEMPERATURE CONVERSION FORMULAS 16-Bit Temperature Data Format 13-Bit Temperature Data Format 10-Bit Temperature Data Format 9-Bit Temperature Data Format REGISTERS STATUS REGISTER CONFIGURATION REGISTER TEMPERATURE VALUE REGISTER ID REGISTER TCRIT SETPOINT REGISTER THYST SETPOINT REGISTER THIGH SETPOINT REGISTER TLOW SETPOINT REGISTER SERIAL INTERFACE SPI COMMAND BYTE WRITING DATA READING DATA INTERFACING TO DSPs OR MICROCONTROLLERS SERIAL INTERFACE RESET INT AND CT OUTPUTS UNDERTEMPERATURE AND OVERTEMPERATURE DETECTION Comparator Mode Interrupt Mode APPLICATIONS INFORMATION THERMAL RESPONSE TIME SUPPLY DECOUPLING POWERING FROM A SWITCHING REGULATOR TEMPERATURE MEASUREMENT QUICK GUIDE TO MEASURING TEMPERATURE OUTLINE DIMENSIONS ORDERING GUIDE