Preliminary Technical Data

ADT7320

Rev. PrA | Page 9 of 24

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:

•

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

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.

Σ-Δ MODULATOR

INTEGRATOR

COMPARATOR

TEMPERATURE

VALUE

REGISTER

CLOCK

GENERATOR

LPF DIGITAL

FILTER

1-BIT

DAC

VOLTAGE REF

AND VPTAT

1-BIT

13-BIT

Figure 11. Σ-∆ Modulator

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

setpoint read/write register), and a low temperature limit (stored

value exceeds these limits, the INT pin is activated; and if it exceeds

programmable for polarity via the configuration register, and

the INT and CT pins are also programmable for interrupt mode

via the configuration register.