2 Comprehensive Summary

To understand the occurrence of the sparkle code, empirical data was collected across multiple devices and multiple configurations, using a test solution that maintains the precise input conditions required to elicit sparkle codes. A detailed evaluation of the results is available further in this document, and a high-level overview of the results is provided in this section.

The custom test solution was created for this project, the hardware was defined to be able to drive the input of the ADC, and use a socket to easily change devices. The most sophisticated aspect of the test solution is the closed servo loop controlling the input voltage to the device. This provided the precise input needed to maintain the input at the necessary voltage for the converter output code to be within half an LSB of the required code transition for multiple hours to allow monitoring for sparkle codes. Details on the test solution used is found later in this document.

A frequency of sparkle code occurrence has been observed to be in the order of parts per billion (ppb) across all configurations and temperatures. At ambient room temperature the highest frequency of sparkles occurred at a clock rate of 2MSPS (125kSPS) at 2.17 sparkle codes per billion conversions. The high and low temperature range are set by the specified minimum and maximum temperature range for the device. At high temperature (125°C) the maximum sparkle rate occurred at 0.329 ppb at VA set to 5 V. At low temperature (-55°C) the maximum sparkle rate occurred at 13.318 ppb at VA set to 5 V. These results are detailed later in this document, and are aligned with design expectations.

Different device configurations were also examined for sparkle code variations. One such configuration is continuous conversion mode, where the CS signal is held low throughout conversions instead of changing state. This configuration did not show any different frequency of sparkle occurrence than previously observed. The effect of multiplexing inputs was also considered, and also showed no variation from the expected. Through all data collection, the sparkle value has been fixed for the respective code transition being observed. No sparkle codes were observed to happen consecutively.

The ADC128S102-SP was released in 2008, with over a decade in the industry. It has a long flight history with numerous successful missions and is the most used ADC in the industry to date. The device has been used across multiple applications and a sparkle code has not been observed during normal operation; it has only been observed in rigorous test conditions. Even then, it is an extremely uncommon occurrence with a very precise controlled input condition, resulting in billions of conversions within that stringent set up for a sparkle code to occur. It is also important to note that since the device’s release, there have not been any changes to fabrication or test procedures of the device.

Although a sparkle code is a rare occurrence, it is a real possibility, and mitigation methods can be put in place to protect the system. Sparkle code occurrences resemble single event transient (SET) signatures, which will be safeguarded for applications with existing mitigation methods. This can result in minimum to no modifications in existing firmware. There are various simple mitigation methods that can be implemented depending on the application. Various methods to mitigate the error will be presented in this document. A best two of three approach is explained in this document and a pseudo code created by Texas Instruments is available in section Software Example.