Datasheet ADT7312 (Analog Devices) - 9

Data Sheet ADT7312 THEORY OF OPERATION CIRCUIT DESCRIPTION
The ADT7312 can be configured to operate in any one of the The ADT7312 is a ±1°C accurate digital temperature sensor following operating modes: that uses a 16-bit ADC to monitor and digitize the temperature • Normal mode (continuous conversion mode) to a resolution of 0.0078°C. By default, the ADC resolution is • One-shot mode set to 13 bits (0.0625°C). • 1 SPS mode An internal temperature sensor generates a voltage proportional • Shutdown mode to absolute temperature; this voltage is compared to an internal
NORMAL MODE (CONTINUOUS CONVERSION
voltage reference and input into a precision digital modulator.
MODE)
The internal temperature sensor has high accuracy and linearity over the entire rated temperature range without the need for In normal mode (default power-on mode), the ADT7312 runs correction or calibration by the user. an automatic conversion sequence. During this automatic con- version sequence, a conversion typical y takes 240 ms to complete. The sensor output is digitized by a sigma-delta (Σ-∆) modu- The ADT7312 is continuously converting: as soon as one tempera- lator, also known as a charge balance type ADC. This type of ture conversion is completed, another temperature conversion converter uses time domain oversampling and a high accuracy begins. Each temperature conversion result is stored in the comparator to deliver 16 bits of resolution in an extremely temperature value register (Register Address 0x02) and is avail- compact circuit. able through the SPI interface. In continuous conversion mode,
CONVERTER ARCHITECTURE
the read operation provides the most recent converted result. The Σ-∆ modulator consists of an input sampler, a summing On power-up, the first conversion is a fast conversion, taking network, an integrator, a comparator, and a 1-bit digital-to- typically 6 ms. If the temperature exceeds 147°C, the CT pin is analog converter (DAC). This architecture creates a negative asserted low. If the temperature exceeds 64°C, the INT pin is feedback loop and minimizes the integrator output by changing asserted low. Fast conversion temperature accuracy is typically the duty cycle of the comparator output in response to input within ±5°C. voltage changes. The comparator samples the output of the The conversion clock for the part is generated internally. No integrator at a much higher rate than the input sampling fre- external clock is required except when reading from and quency. This oversampling spreads the quantization noise over writing to the serial port. a much wider band than that of the input signal, improving overall noise performance and increasing accuracy. The measured temperature value is compared with a critical temperature limit (stored in the 16-bit T The modulated output of the comparator is encoded using CRIT setpoint register), a high temperature limit (stored in the 16-bit T a circuit technique that results in SPI temperature data. HIGH setpoint register), and a low temperature limit (stored in the 16-bit TLOW
Σ-Δ MODUL
setpoint register). If the measured value exceeds the THIGH or
ATOR
TLOW limit, the INT pin is activated; if the measured value
INTEGRATOR COMPARATOR
exceeds the TCRIT limit, the CT pin is activated. The polarity of
VOLTAGE
the INT and CT pins is programmable using the configuration
REFERENCE
register (Register Address 0x01). The INT and CT pins are also programmable for interrupt mode via the configuration register.
1-BIT DAC 1 BIT TEMPERATURE CLOCK LPF DIGITAL VALUE
1 1
GENERATOR FILTER
0
REGISTER 13/16 BITS
06791- Figure 10. Σ-∆ Modulator Rev. A | 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 Pad Configuration and Function Descriptions Die Bond Pad Coordinates Typical Performance Characteristics Theory of Operation Circuit Description Converter Architecture Normal Mode (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 Resetting the Serial Interface INT and CT Outputs Undertemperature and Overtemperature Detection Comparator Mode Interrupt Mode Redundant Critical Generator 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