SD Memory Card Design-in
Swissbit has been one of the leading suppliers of SD Memory Cards for industrial use as well as for the automotive industry for many years.
This TechNote was created from this experience. It focuses on the most common problems that may occur during the integration of an SD Memory interface and is intended to serve as guide to avoid these problems.
Power Failure Testing
A sudden power failure can lead to various problems with flash media, resulting in a total failure, which is the worst case. This can be remedied by storage media that can still write all the data in the cache to the flash, recognizable by the addition PLP (Power Loss Protection).
But how to test the robustness against sudden power failures as part of product qualification? Our latest TechNote gives a detailed insight and provides an instruction for building your own test hardware.
Whether a flash storage medium is suitable for the intended use case can be determined in advance using the data sheet. Depending on the manufacturer, however, different test methods are used, which means that the resulting values are not always easy to compare with products from other manufacturers.
The typical methods, programs and terms that are used for such measurements are explained in this TechNote to provide a way to better compare the characteristics of different SSDs and match them with the intended use.
NAND Flash Endurance Testing
Typical application scenarios for NAND flash memory assume a service life of 3–5 years and in some cases even significantly longer. The flash type to be used (SLC, pSLC, MLC, TLC, QLC) is selected accordingly, which has the necessary endurance, i. e. the lifespan measured in erase and programming cycles.
If the specified endurance is to be checked as part of the qualification of a NAND flash memory for a project, the rate of aging has a significant influence on the result.
The presence of factory bad blocks in NAND flash is as much a technology reason as the occurrence of additional bad blocks during the lifetime.
Both are no (negative) quality indications.
However, with the occurrence of bad blocks during the lifetime, the correct handling of these events by the firmware is critical in order not to lose the new data as well as the already stored data of such blocks.
To compare speed specifications in data sheets of NAND flash memory media, the test conditions must be identical. If the measurement was not started repeatedly or did not cover the entire logical address space, the specified speed can be significantly higher than the real achievable speed.
Unlike hard drives or NOR flash, NAND flash does not have a fixed mapping of logical memory addresses to physical memory addresses.
The assignment takes place via mapping tables, which are managed by the firmware of the storage medium.