EMBEDDED-FEATURE

How can Embedded Applications Ensure Small Density NOR Flash Product Longevity?

Grant Hulse

Product Marketing Manager, Memory Products Division, Microchip Technology

Typically, most small standalone and embedded systems contain an 8-bit or 16-bit microcontroller (MCU) surrounded by a collection of analog and sensor integrated circuits (ICs), display and communication interface ICs. Garage door openers, electric drills, manufacturing line equipment, medical analysis systems, etc. tend to fall under this category. Sometimes, they might even require, SRAM, EEPROM, and NOR Flash ICs if these are not present in the selected microcontroller (See Figure 1). For end equipment makers, longevity of NOR Flash ICs is a concern. Since larger density NOR Flash family members (256 Mbit to 1 Gbit+) drive the memory vendors’ business decisions, there is a constant push for smaller geometry processes and shorter product life cycles. When a move to a new process node causes an IC supplier to announce an end-of-life (EOL), it becomes necessary to requalify the device. This adds unexpected spend to existing programs since engineering resources often need to be diverted. Microchip Technology has a solution to address the NOR Flash longevity problem.

The Outlook for Small Density Memory

As NOR Flash suppliers focus on bringing the most value and lowest cost points to their customers, they have increasingly been leaving behind their smaller density products in favour of high-margin, high-volume, high-density memory parts. The industry has been evolving towards higher density as lower density products reach EOL. These IC disruptions require that 20-year-product-life embedded system suppliers explore not just new versions of parts, but sometimes new suppliers altogether. One approach to tackle this is to use a 128-Mbit NOR Flash IC to hold 4 Mbits of user programming code, thereby ‘futureproofing’ the system design. However, this can mean inefficient power consumption and higher overall system cost. Another way could be to seek out a non-traditional NOR Flash memory supplier that is equipped to supply the same memory product for 20+ years. This may result in a higher upfront cost but might work out over the course of time when one factors in the cost of requalification and involvement of engineering resources.

Microchip recognized the negative impact of this density trend on business plans and business objectives several years go. In order to remedy this, it emerged as a non-traditional NOR Flash memory IC supplier that offers serial SRAM IC, serial EEPROM IC, analog, and sensor IC products as well. Currently, it only provides for NOR Flash memory up to 64 Mbit densities, where focused memory suppliers will continue to supply product for the next 20 or more years.

Figure 1 represents a microcontroller surrounded by other integrated circuit pieces. This gives the embedded application life and purpose. Here, the touchscreen display output IC shares a few different display images contained within the 8 Mbit NOR Flash [highlighted] as dictated by the program code (embedded in the microcontroller in this case). The key characteristics of this external NOR Flash memory IC are 1) 8 Mbits, 2) standard SPI interface, 3) low standby current, 4) low write current, 5) small area, and 6) available in production for 20 years.

Figure 1. With the microcontroller at the heart of an embedded system, several other IC technologies, including NOR Flash, are required for specific applications.

Table 1 compares a 128 Mbit NOR Flash IC for future proofing versus an 8 Mbit NOR Flash that has long term availability from a non-traditional memory supplier. Clearly, the 8 Mbit NOR Flash IC is best suited to meet the embedded application requirements.

Table 1. A 128 Mbit NOR Flash IC compared to an 8 Mbit NOR Flash IC reveals obvious advantages.

Using Small Density NOR Flash

As discussed, while large NOR Flash suppliers might choose not to focus on low-density NOR Flash from a strategic point of view, it makes sense for an embedded company’s product offerings and full-system-solution strategy. For instance, most homes today include several dozens of embedded systems (kitchen appliances, white goods, tools, etc.) with 8-bit, 16bit or even 32-bit MCUs that do not require a large amount of code. In these system, only small amounts of NOR Flash are needed to provide program code, calibration data, calibration parameters, event logs and more.

There are several situations (such as in Figure 1) where external NOR Flash makes more sense than MCUs that come with built-in flash. For instance, there are cases where the cost tradeoff between total system bill of material (BOM) and offered microcontroller FLASH sizes works in favour of external NOR Flash. Other instances could include microcontroller function mismatch, quicker reflash time for test sets during line manufacturing, and system reflash events for field upgrades.

Small NOR Flash is also used for Application Programming, boot code and execute-in-place (XIP) operation in lower gate count application-specific integrated circuits (ASICs) such as field-programmable gate arrays (FPGAs) and complex programmable logic devices (CPLDs). For XIP applications offering low standby power consumption, NOR Flash memory ICs work well since they are directly accessible using a standard serial interface such as SPI.

NOR Flash memory devices are also very board efficient since they are available in 8-pin packages, such as an 8-lead SOIC and 8-contact WDFN (6mm x 5mm), and small density as well. For applications where limited board space is a challenge, such as an electric toothbrush, a Wafer Level Chip Scale Package (WLCSP) can help achieve significant package space savings (almost 69%) as shown in Figure 2.

Figure 2. Packaging size for an 8 Mbit versus a 128 Mb Wafer Level Chip Scale Package

1000X Faster ReFlash Times

Despite being a nontraditional memory supplier, Microchip ships a large number of microcontrollers with FLASH memory. Flash memory with SuperFlash® technology is designed to provide block erase times 20x faster and full chip erase 1000x faster, proving a significant technical and strategic advantage. While not commonly adopted by large NOR Flash memory suppliers, reflashing a NOR Flash helps lower manufacturing costs and allows for quicker low power field system upgrades. For example, the 8 Mbit NOR Flash (with the SuperFlash enhancement) has a block max erase time of only 25 ms, which is 30 times faster as compared to a 128 Mbit NOR Flash (without SuperFlash technology), which has a typical max block erase time of 0.7 to 1 second. Time savings aside, every block erase for a rewrite cycle also brings in a power difference of ~800 ms * 33 mA.

Embed NOR Flash in New Designs

Microchip Technology has an established practice to ensure availability for as long as customers need replacement products, even if some suppliers may be exiting NOR Flash memory products and even declaring EOLs. By committing to this availability for midsize, small and even large volume applications, Microchip ensures that customers can get what the embedded system needs as long as needed. SuperFlash is a registered trademark of Microchip Technology.