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AT30TS74 [PRELIMINARY DATASHEET]

Atmel-8897D-DTS-AT30TS74-Datasheet_102014

4.3

Temperature Measurements

The AT30TS74 utilizes a band-gap type temperature sensor with an internal sigma-delta Analog-to-Digital

Converter (ADC) to measure and convert the temperature reading into a digital value with a selectable

resolution as high as 0.0625

C. The measured temperature is calibrated in degrees Celsius; therefore, a lookup

table or conversion routine is necessary for applications that wish to deal in degrees Fahrenheit.

The result of the digitized temperature measurements are stored in the internal Temperature Register of the

AT30TS74, which is readable at any time through the device's serial interface. When in the normal operating

mode, the device performs continuous temperature measurements and updates the contents of the

Temperature Register (see Section 5.2, “Temperature Register”) after each analog-to-digital conversion.

The resolution of the temperature measurement data can be configured to 9, 10, 11, or 12 bits which corresponds

to temperature increments of 0.5

C, 0.25C, 0.125C, and 0.0625C, respectively. Selecting the temperature

resolution is done using the R1 and R0 bits in the Configuration Register (see Section 5.3, “Configuration

Register”). The ADC conversion time does increase with each bit of higher resolution, so careful consideration

should be given to the resolution versus conversion time relationship. The default resolution after device

power-up or reset is nine bits, which retains backwards compatibility to industry-standard LM75-type devices.

With 12 bits of resolution, the AT30TS74 can theoretically measure a temperature range of 255

C (-128C to

+127

C); however, the device is only designed to measure temperatures over a range of -55C to +125C.

4.4

Temperature Alarm

After the measured temperature value has been stored into the Temperature Register, the data will be

Limits”), then the device will activate the ALERT output pin.

The polarity and function of the ALERT pin can be configured by using specific bits in the Configuration

Register. The ALERT pin defaults to the active low state after device power-up or reset but can be reconfigured

to active high by setting the POL bit in the Configuration Register to a Logic 1. The function of the ALERT pin

changes based on the Alarm Thermostat mode, which can be configured to either Comparator mode (see

Section 4.4.2, “Comparator Mode”) or Interrupt mode (see Section 4.4.3, “Interrupt Mode”) by using the

CMP/INT bit in the Configuration Register. The Comparator mode is the default operating mode after the device

powers up or resets.

otherwise, the ALERT pin will output erroneous results and will falsely signal temperature alarms.

4.4.1

Fault Tolerance Limits

A temperature fault occurs if the measured temperature meets or exceeds either the high temperature limit set

due to environmental or temperature noise, the device incorporates a fault tolerance queue that requires

consecutive temperature faults to occur before resulting in a valid fault condition. The fault tolerance queue

value is controlled by the FT1 and FT0 bits in the Configuration Register and can be set to a single fault count of

1 or a count of 2, 4, or 6 consecutive faults.

An internal counter that automatically increments after a temperature fault is used to determine if the fault

tolerance queue setting has been met. After incrementing the fault counter, the device will compare the count to

the fault tolerance queue setting to see if a valid fault condition should be triggered. Once a valid fault condition

occurs, the device will activate the ALERT output pin. If the most recent measured temperature does not meet

or exceed the high or low temperature limit, then the internal fault counter will be reset back to zero.