AVX and IoT Devices

IoT has the ability to be implemented everywhere and with such benefits Gartner estimates 26 billion IoT devices installed by 2020 with $300 incremental revenue in services resulting.
Suppliers to the IoT design community are creating whole new chipsets to address the goals of IoT devices. 

IoT designers have a difficult end goal:

To create miniature modules that commonly measure physical conditions (temperature, humidity, vibration, etc.), use low amounts power and exhibit long lifetimes.

Extreme attention is given to the topic of power sources and power consumption. With the correct selection of ICs, IoT modules can exhibit active power consumption levels - in the 6ma range and sleep mode in the 1ua region. These levels of power consumption enable some IoT modules to be capable of operating indefinitely - without a battery or connections to external power but powered by energy harvesters.

This discussion centers on component options designers have in Power, Sensor Input, Output matching and Timing blocks. 

Power

Both tantalum and ceramic capacitors are an excellent choice for the power section of an IoT module.

Tantalum capacitors can provide extremely large values of capacitance in small packages. Values can be so large that Tantalum capacitors can become the energy storage source for energy harvesting powered modules. Specifically, three tantalum capacitor types hold advantages for designers to consider – TAJ, TRJ, TCN series. 

Regardless of the particular series chosen de-rating plays an important role in decreasing the leakage current of Tantalum capacitors in application. 

The figure below shows the reduction of leakage current in Tantalum capacitors as the ratio of applied voltage to rated voltage decreases. Using a part with a higher rated voltage than the application voltage is referred to as “voltage de-rating”. The greater the level of voltage de-rating, the lower the leakage current level in the application. 

A part used at 50% of its rated voltage will have more than 3 times lower leakage levels than one used at 80%. 

Leakage Current vs. Applied Voltage

AVX has three series within its tantalum family that exhibit performance beneficial to IoT designs.

The TAJ Low profile series is a general purpose, low profile Tantalum Capacitor. Although Tantalum capacitors can be purchased in sizes as small as 0201, the high volume use and availability of TAJ devices >/= 0805 capacitors was considered to be important to IoT designs based upon wide spread use, respectable capacitance range and the probability that leakage could be made very low with appropriate de-rating.

AVX TRJ Professional Series Tantalum Capacitors offer reduced DCL performance at case sizes and voltages deemed acceptable to IoT designers.

The TCN – Conductive Polymer “Under Tab” or “Face Down” termination style Capacitors offer a very wide capacitance range with a benign failure mode. The higher levels of leakage of Tantalum Polymer capacitors can be brought within acceptable limits with conservative voltage de-rating. The under tab termination style enables an increase in volumetric efficiency (more capacitance in a given size / voltage rating) than the traditional J-lead termination style.

A comparison of these commonly used Tantalum capacitors is shown in the below table. 

As previously mentioned, Ceramic capacitors – in particular X5R dielectrics have the ability to provide large values in miniature sizes. AVX X5R capacitors are available in case sizes from 01005 to 1812, voltage ratings from 4-100v and values from 100pf to 100uf.

Additional information on AVX X5R capacitors is available at: https://www.arrow.com/en/products/12104d107mat2a/avx

Input Sensor Support

The application environments that Iot devices encounter will vary widely. Therefore, transient and EMI protection are commonly used to ensure that IoT modules will work acceptably across the spectrum on end applications.

Multilayer varistors (MLVs) are an attractive design option for the designer to control both transient voltage threats as well as EMI with the use of a single component. AVXs MLVs - TransGuard® are zinc oxide (ZnO) based ceramic semiconductor device with non-linear voltage-current characteristics (bi-directional) similar to back-to-back zener diodes. They have the added advantage of greater current and energy handling capabilities as well as EMI/RFI attenuation.

MLVs are fabricated by a ceramic sintering process that yields a structure of conductive ZnO grains surrounded by electrically insulating barriers, creating varistor-like behavior. The number of grain-boundary interfaces between conducting electrodes determines “Breakdown Voltage” of the device. High voltage applications such as AC line protection require many grains between electrodes while low voltage requires few grains to establish the appropriate breakdown voltage.

MLVs are manufactured by mixing ceramic powder in an organic binder (slurry) and casting it into thin layers of precision thickness. Metal electrodes are deposited onto the green ceramic layers which are then stacked to form a laminated structure. The metal electrodes are arranged so that their terminations alternate from one end of the varistor to the other. The device becomes a monolithic block during the sintering (firing) cycle providing uniform energy dissipation in a small volume.

The equivalent model for a MLV is shown below. This model shows that MLVs act like an EMI filter capacitor in the off state with the off state capacitance element exhibiting stability characteristics close to an X7R capacitor. Capacitance values range from <<1pf (useful for sensor protection without capacitive loading) to >16nf (useful for low frequency noise attenuation.

MLV Equivalent Model

AVX has created a series of MLVs with ultra-low leakage intended for energy harvesting applications and long life coin cell applications. These devices exhibit a consistent low leakage current across time and temperature at voltages common to IoT applications. An example of the leakage current improvements of this process is shown below.

Output Matching

A wide variety of inductor choices exist for output matching of IoT modules.

The LCWC series of wire wound ceramic inductors includes ultra-compact inductors (case sizes 0402 to 1206) that provide high Q factors, with a high current ranges. LCWC has a tight tolerance (as tight as ±2%) and an operating temperature of -40ºC to +125ºC.

The LCMC is a multilayer ceramic material high frequency chip inductor construction for high frequency applications up to 10GHz. LCMC inductors case sizes range from 0201 to 0603 
These RF chip inductors offer currents up to 1 amp and a value range of 0.3nH to 470uH.

AVX Accu-L Inductors are based on thin-film multilayer technology. The technology provides a miniature part with excellent high frequency performance and rugged construction for reliable automatic assembly. Thin film inductors featuring extreme lot-to-lot repeatability and tight tolerance. The use of very low-loss dielectric materials, silicon dioxide and silicon oxynitride, in conjunction with highly conductive electrode metals results in low ESR and high Q. These high-frequency characteristics change at a slower rate with increasing frequency than for ceramic microwave inductors.

MLO inductors are an 0402 case size low DCR tight tolerance inductor series. They have an ability to withstand high transient voltages without parametric shift, match FR-4 TCE and are low profile.

A series of comparison tables of these inductor technologies is shown below. 

 

Common options for IoT timing follow: