ADT7320UCPZ AD [Analog Devices], ADT7320UCPZ Datasheet - Page 9

• Manufacturer Part Number: ADT7320UCPZ
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
THEORY OF OPERATION
CIRCUIT INFORMATION
The ADT7320 is a 13-bit digital temperature sensor that is
extendable 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 excellent accuracy and
linearity over the entire rated temperature range without
needing correction or calibration by the user.
The sensor output is digitized by a Σ-Δ modulator, also known
as the charge balance type ADC. This type of converter uses
time-domain oversampling and a high accuracy comparator to
deliver 16 bits of resolution in an extremely compact circuit.
Configuration register functions consist of the following:
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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 the 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 SPI temperature data.
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
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TEMPERATURE MEASUREMENT
In normal mode, the ADT7320 runs an automatic conversion
sequence. During this automatic conversion sequence, a
conversion takes 240 ms to complete and the ADT7320 is
continuously converting. This means that as soon as one
temperature conversion is completed, another temperature
conversion begins. Each temperature conversion result is
stored in the temperature value register and is available
through the SPI interface. In continuous conversion mode,
the read operation provides the most recent converted result.
At 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 T
register), a high temperature limit (stored in the 16-bit T
setpoint read/write register), and a low temperature limit (stored
in the 16-bit T
value exceeds these limits, the INT pin is activated; and if it exceeds
the T
programmable for polarity via the configuration register, and
the INT and CT pins are also programmable for interrupt mode
via the configuration register.
VOLTAGE REF
GENERATOR
AND VPTAT
CLOCK
CRIT
limit, the CT pin is activated. The INT and CT pins are
LOW
setpoint read/write register). If the measured
Figure 11. Σ-∆ Modulator
INTEGRATOR
Σ-Δ MODULATOR
LPF DIGITAL
1-BIT
DAC
FILTER
COMPARATOR
CRIT
1-BIT
13-BIT
setpoint read/write
TEMPERATURE
ADT7320
REGISTER
VALUE
HIGH