What is a Single-Channel Digital Temperature Sensor (DTS)?

One of the most popular temperature sensor types in almost every application market segment in use today is a single-channel Digital Temperature Sensor (DTS). A single-channel DTS is a complete temperature monitoring system available in small compact packages with temperature accuracy capabilities of ± 0.25°C across a wide temperature range, like -40°C to 125°C. Simply place the DTS on a circuit board. Once it is connected and powered properly, the temperature sensor will measure and internally convert measured temperature to a digital value that can be easily read via a host controller.

DTSs are available in two popular standard protocol types for communication, namely I²C and Serial Peripheral Interface (SPI). The focus of this article is on I²C single-channel DTSs. Single-channel means the device can monitor one temperature location by measuring its own die temperature, sensed through the leads of the part with circuit board traces.

I²C temperature sensors can be categorized into two industry-standard protocol classes; LM75-type or Jedec Standard. We will focus on the LM75-type for this discussion. An advantage of using LM75-type temperature sensors is the capability to customize settings via the internal registers inside the temperature sensor to tailor specific operating conditions and functionality per your system needs.

Let’s discuss the LM75-type temperature sensor’s internal register structure and functionality. They contain four basic internal registers:

  • Pointer register
  • Configuration register
  • High temperature (THIGH) limit register
  • Low temperature (TLOW) limit register

These registers enable you to set and customize the temperature sensor’s operational settings during the initialization process by the host controller after power-up, except for the temperature register, but more on this later. The pointer register allows access to one of the four registers by pointing to the selected register indirectly. The configuration, TLOW and THIGH limit and temperature registers cannot be directly accessed by I²C software commands and can only be accessed through the use of the pointer register as illustrated below.

RegistersTempSensor.jpg
Diagram illustrating the standard registers found in typical digital output temp sensors

The configuration register is used to control key operational modes and settings of the device such as the temperature conversion resolution, the fault tolerance queue, the ALERT pin polarity, the Alarm Thermostat mode, and the Shutdown mode. Some devices on the market also have a One-Shot mode. The One-Shot mode is a power-saving mode to allow the device to come out of Standby mode to take a temperature measurement, update the temperature register, then return to Standby mode, making this a great feature in battery-powered applications.

The temperature register is a read-only register that stores the digitized value of the most recent temperature measurement and can simply be read for the latest temperature measurement. The temperature register can be read at any time and since temperature measurements are performed in the background, reading the temperature register does not affect any other operation that may be in progress.

The TLOW and THIGH limit registers store the user-programmable lower and upper temperature limits for the temperature alarm. The following diagram illustrates a typical temperature profile. For example, if you set the TLOW and THIGH limit registers to 85°C and 50°C respectively, the temperature sensor will set flags and can drive its output pin to notify the host controller when either limit value is exceeded.

TempMeasurements.jpg

This graph shows temperature measurements, including when the temperature went outside of the TLOW and THIGH limit registers.

To learn more about our single-channel DTSs product offerings, please visit the Temperature Sensors page.

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