AT30TS75 [DATASHEET]
Atmel-8748E-DTS-AT30TS75-Datasheet_092013
10
5.2 Temperature Measurements
The AT30TS75 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
0.0625qC. 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 AT30TS75,
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
6.2, “Temperature Register” on page 16) 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 0.5qC, 0.25qC, 0.125qC, and 0.0625qC, respectively. Selecting the temperature resolution is
done using the R1 and R0 bits in the Configuration Register (see Section 6.3, “Configuration Register” on page 18). 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 AT30TS75 can theoretically measure a temperature range of 255qC (-128qC to +127qC);
however, the device is only designed to measure temperatures over a range of -55qC to +125qC.
5.3 Temperature Alarm
After the measured temperature value has been stored into the Temperature Register, the data will be compared with
both the high and low temperature limits defined by the values stored in the T
HIGH
Limit Register and T
LOW
Limit Register.
If the comparison results in a valid fault condition (see Section 5.3.1, “Fault Tolerance Limits” on page 10), 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 5.3.2, “Comparator Mode” on page
11) or Interrupt mode (see Section 5.3.3, “Interrupt Mode” on page 12) 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.
The value of the high temperature limit stored in the T
HIGH
Limit Register must be greater than the value of the low
temperature limit stored in the T
LOW
Limit Register in order for the ALERT function to work properly; otherwise, the
ALERT pin will output erroneous results and will falsely signal temperature alarms.
5.3.1 Fault Tolerance Limits
A temperature fault occurs if the measured temperature meets or exceeds either the high temperature limit set by the
T
HIGH
Limit Register or the low temperature limit set by the T
LOW
Limit Register. To prevent false alarms 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.
Figure 5-2 shows a sample temperature profile and how each temperature fault would impact the internal fault counter.
