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Data Sheet

ADT7320

Rev. 0 | Page 9 of 24

THEORY OF OPERATION

CIRCUIT INFORMATION

The ADT7320 is a high accuracy digital temperature sensor that

uses a 16-bit ADC to monitor and digitize the temperature to a

resolution of 0.0078°C. By default, the ADC resolution is set to

13 bits (0.0625°C). An internal temperature sensor generates a

voltage proportional to absolute temperature; this voltage is

compared to an internal voltage reference and input into a

precision digital modulator.

The internal temperature sensor has high accuracy and linearity

over the entire rated temperature range without the need for

correction or calibration by the user.

The sensor output is digitized by a sigma-delta (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.

CONVERTER DETAILS

The Σ-Δ modulator consists of an input sampler, a summing

network, an integrator, a comparator, and a 1-bit digital-to-analog

converter (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-∆ MODULATOR

INTEGRATOR

COMPARATOR

TEMPERATURE

VALUE

CLOCK

GENERATOR

LPF DIGITAL

FILTER

1-BIT

DAC

VOLTAGE

REFERENCE

1-BIT

13-/16-BIT

Figure 11. Σ-∆ Modulator

The ADT7320 can be configured to operate in any one of the

following four operating modes: normal mode, one-shot mode,

1 SPS mode, and shutdown mode.

CONTINUOUS CONVERSION MODE

In continuous conversion mode (default power-up 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.

On power-up, the first conversion is a fast conversion, taking

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

asserted 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 TCRIT setpoint register), a

high temperature limit (stored in the 16-bit THIGH setpoint

setpoint register). If the measured value exceeds the high or low

temperature limits, the INT pin is activated; if it exceeds the TCRIT

limit, the CT pin is activated. The polarity of the INT and CT

pins is programmable for via the configuration register, and the

INT and CT pins are also programmable for interrupt mode via

the configuration register.

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