A Replacement to LM75/TMP75 Digital Temperature Sensors: The Texas Instruments TMP1075

Texas Instruments announces their new TMP1075, which is a replacement to the industry standard LM75 and TMP75 digital temperature sensors.

Texas Instruments' TMP1075 is a digital temperature sensor that is said to be "optimal for thermal management and thermal protection applications," according to the TMP1075 datasheet. Although thermal pathways are routed through the package leads as well as the plastic package itself, the package leads serve as the principal thermal conduits because they are made of metal, and, therefore, have lower thermal resistance. The image below illustrates how the IC itself, actually the internal diode temperature sensor, functions as the temperature sensing device.

 

This block diagram depicts how the TMP1075 is a fully-integrated digital temperature sensor. From the datasheet (PDF).

Getting the Most out of This Sensor

In order to take full advantage of what this digital temperature-sensing IC offers, Texas Instruments has been generous by providing their Detailed Design Procedure in Section 8.2.2 (on page 21). Included in this section is the recommendation—although it may seem like common sense...but such reminders are oftentimes welcome—of placing the TMP1075 in close proximity to the heat source. And because proper PCB layout is a crucial design step of such temperature sensors, TI has also provided the following layout example. Take note of the large copper area underneath the IC.

TI shows us preferred IC placement (with respect to the heat source), and that using plenty of copper underneath the IC (for thermal coupling) is encouraged. Image taken from the datasheet (PDF).

Uses I3C...What's I3C?

Not to be confused with I2C, although the two are somewhat related, I3C provides added benefits by, according to MIPI.org, "incorporating, consolidating and advancing I2C, SPI and UART with a new approach." This international organization goes on to state that this design approach provides a superset of features and functionalities all the while supporting legacy devices. Seems impressive! In all honesty, prior to reading this datasheet I had never heard of I3C. Do you have any experience using I3C, good or bad? If so, please share your experience with us in the comments section.

Achieves 32 Distinctive Addresses... Using Only Three ADDR Pins

In a previous article, I mentioned how some I2C devices make use of different resistor values for assigning unique I2C addresses. Now, what I find to be equally impressive is that only three ADDR lines are needed for creating 32 individual addresses. As can be seen in the figure below, the secret to this solution is accomplished by using the SCL and SDA lines, in addition to power and ground, when assigning the addresses. This creates 4-state options on pins A0 and A1 to provide 16 possibilities. Pin A2 has 2-state options bringing the total to 32. I'm wondering if it works as flawlessly, and as easily, as it appears. Do you have any experience with this addressing design approach? If so, please share your insights in the comments section. Thanks!

This table, from the datasheet, shows us that I2C SCL and SDA lines are used together with power (logic 1) and ground (logic 0) for assigning I2C addresses. Amazing!

A Word about Minor Documentation Goofs

During my read of this datasheet, I spotted a few minor documentation goofs. And to be frank, I have found that similar documentation goofs are not uncommon in brand new datasheets. Still, they may be a bit embarrassing for some companies. Hopefully, TI will clean up these slight oversights in the next datasheet revision. Some are innocuous, such as the repeat, verbatim, of the paragraph explaining the One-Shot (OS) features. (Or, perhaps, TI is so extremely proud of this feature that they felt it deserved being acknowledgment twice?)

Other documentation goofs, however, could be a tad more serious, such as the listing of the incorrect operating temperature range in the packaging/part numbering table. While the operating temperature specification is shown to be from -55°C to 125°C (see the image below), the packaging/part numbering table (the subsequent image) shows us a range from -40°C to 125°C.

This table, from the datasheet, tells us that -55°C to 125°C is the device's operating temperature range...

 

...but this table, again from the datasheet, tells us a different story.

It's important to keep an eye out for the latter kind of documentation errors as they can cause hiccups in the usage of the component in question.



Have you had an opportunity to use this new digital temperature sensor, from TI, in any of your designs? If so, please share your experience with us in the comments section.