Datasheet ADT7311 (Analog Devices) - 9

Data Sheet ADT7311 THEORY OF OPERATION CIRCUIT INFORMATION Σ-∆ MODULATOR
The ADT7311 is a high accuracy digital temperature sensor that
INTEGRATOR COMPARATOR
uses a 16-bit ADC to monitor and digitize the temperature to
VOLTAGE REF
0.0078°C of resolution. The ADC resolution, by default, is set to
AND VPTAT
13 bits (0.0625°C). An internal temperature sensor generates a voltage proportional to absolute temperature, which is com-
1-BIT
pared to an internal voltage reference and input into a precision
DAC
digital modulator.
1-BIT
The internal temperature sensor has high accuracy and linearity
CLOCK LPF DIGITAL TEMPERATURE
2 over the entire rated temperature range without needing correc- 1
GENERATOR FILTER VALUE
0
13-BIT/
0- 05 tion or calibration by the user.
REGISTER 16-BIT
09 Figure 11. Σ-∆ Modulator The sensor output is digitized by a sigma-delta (Σ-Δ) modulator, also known as the charge balance type analog-to-digital conver-
TEMPERATURE MEASUREMENT
ter. This type of converter utilizes time-domain oversampling In normal mode (default power-up mode), the ADT7311 runs and a high accuracy comparator to deliver 16 bits of resolution an automatic conversion sequence. During this automatic in an extremely compact circuit. conversion sequence, a conversion typically takes 240 ms to
CONVERTER DETAILS
complete and the ADT7311 is continuously converting. This means that as soon as one temperature conversion is completed, The Σ-Δ modulator consists of an input sampler, a summing another temperature conversion begins. Each temperature network, an integrator, a comparator, and a 1-bit DAC. This conversion result is stored in the temperature value register and architecture creates a negative feedback loop and minimizes the is available through the SPI interface. In continuous conversion integrator output by changing the duty cycle of the comparator mode, the read operation provides the most recent converted output in response to input voltage changes. The comparator result. samples the output of the integrator at a much higher rate than the input sampling frequency. This oversampling spreads the On power-up, the first conversion is a fast conversion, taking quantization noise over a much wider band than that of the typically 6 ms. If the temperature exceeds 147°C, the CT pin input signal, improving overall noise performance and asserts low. If the temperature exceeds 64°C, the INT pin asserts increasing accuracy. low. Fast conversion temperature accuracy is typically within ±5°C. The modulated output of the comparator is encoded using a The conversion clock for the part is generated internally. circuit technique that results in SPI temperature data. 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 setpoint 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. 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 TEMPERATURE MEASUREMENT ONE-SHOT MODE 1 SPS MODE CT and INT Operation in One-Shot Mode SHUTDOWN 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 PERIPHERAL 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 MONITORING QUICK GUIDE TO MEASURING TEMPERATURE OUTLINE DIMENSIONS ORDERING GUIDE AUTOMOTIVE PRODUCTS