Two Tiny Form Factors: An NFC Sensor Tag and Data Logger IC from ams

A new tiny sensor tag and data logger IC offers efficient and accurate monitoring of sensitive assets.

ams recently released the AS39513 NFC (near-field communication) sensor tag and data logger for smart labels. As we'll discuss below, this IC is able to work with and without a battery, uses an "SPI-like" interface for chip initialization and for microcontroller communications, includes an RTC (real-time clock) and associated time-stamp functionality, has an on-board temperature sensor, and is available in two package types: tiny and tiny.

The figure below, from the datasheet, depicts the functional blocks in this fully ISO 15693 and NFC-V (T5T) compliant IC.

 

Functional blocks of the AS39513. Drawing taken from the datasheet (PDF).

The general idea here is a digital-sensor-plus-data-storage device that is compatible with NFC and that can be easily integrated into electronic labels for food, healthcare products, manufactured items, etc.

Operates with or without a Battery

While this IC is best suited for applications that use thin and flexible batteries, it can also operate using the power provided by an RF field generated by an RFID reader. The datasheet describes this “works without a battery” feature as passive operation.
If you're planning to use a battery in your NFC sensor tag application, then be mindful that, according to the Power Management section (page 12) of the datasheet, while this IC supports either a single-cell battery (typically 1.5 V) or a dual-cell battery (typically 3 V), it does not support a continuous battery range from 1.35 V to 3.3 V (see the following figure).

The IC's discontinuous supply voltage range seems a bit odd. From the datasheet (PDF).

However, while the figure below (the datasheet's Figure 7) seems to support the discontinuous voltage range notion, the subsequent figure (Figure 9) clearly states that a voltage range of 1.35 to 3.6 V is acceptable. So, if I were planning to use this device in one of my designs, I would definitely contact ams to ask for clarification on the IC's operating voltage range.

Battery supply voltage range of the AS39513. Note that a continuous range from 1.35V to 3.3V is not supported. Table from the datasheet (PDF).

 

But this table from the datasheet shows us a continuous voltage range.

An "SPI-like" Bus Interface

When it comes to chip testing and initialization, as well as communicating with a microcontroller, this IC uses an "SPI-like" interface. As described in the datasheet's section entitled Slave Serial Interface (SPI-like), this communication interface scheme employs an active high CE (chip enable) signal, as opposed to the active low CE signal normally utilized by SPI interfaces.
For more information on this interface, refer to the section entitled SPI Commands on page 92 of the datasheet. I'm a little puzzled as to why ams didn't simply use the "normal" SPI interface protocol.

Write and read transactions for the SPI-like interface. Diagrams taken from the datasheet.

Real-Time Clock

The AS39513 has an on-board RTC (real-time clock) that can be used for logging data (with time stamps) and for device lifetime tracking. Logging intervals ranging from 1 second to 9.1 hours are supported. However, the RTC’s accuracy is ±3%, so it’s not intended for high-precision timing requirements.

Two Tiny Package Options and a Look at Temperature Accuracy

The AS39513 is available in two package flavors: the thin WL-CSP (wafer level chip scale package), which measures 2.268 × 2.358 × 0.316 mm, and the gold-bumped die package, which offers a slightly thinner profile (0.300 mm).
Now, when considering the very similar dimensions between these two package types, I'm asking myself, "Why does ams offer two package options at all?"
Perhaps the answer lies in the accuracy of the IC's on-chip temperature sensor. Specifically, the datasheet states that the on-chip temperature sensor has a range from -20°C to 55°C, but only the gold-bumped-die device is specified as having an accuracy of ±0.5°C from -20°C to 10°C. The accuracy of the WL-CSP device isn't given in the datasheet. But there’s no obvious reason why they couldn’t achieve this same accuracy in the other package. Maybe ams knew that certain applications would need that slightly thinner form factor. If you know why this is the case, let us know in the comments.
One final comment regarding temperature measurements: The datasheet's section entitled Temperature Sensor tells us that while the IC's on-chip temperature sensor can be reconfigured for a number of different temperature ranges, after each temperature-range change the sensor requires recalibration. Good to know. A quick search through the datasheet did not reveal much information about what exactly is required to perform the recalibration.

Demo Kit

If you're interested in testing the features and functionalities of the AS39513, there's an associated demo kit available. According to ams, this "out of the box" and ready-for-action demo kit can be used with an NFC-enabled smartphone (Android app included) or a dedicated RFID reader that supports the ISO 15693 standard.

 

The AS39513 demo board. Image taken from ams.com.

Have you had a chance to use this new NFC sensor tag and data logger IC in any of your designs or the demo kit? If so, leave a comment and tell us about your experiences.