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Two Solutions Based on Memory Device Loss of Power and UPS Circuit Design Ideas of Farad Capacitor
Nand-Flash and eMMC (Nand-Flash with an integrated flash controller) are non-linear memory macrocells that offer a cost-effective solution for solid-state mass storage. These technologies provide large storage capacities and fast data rewriting speeds, making them ideal for applications that require handling vast amounts of data. As a result, they are widely used in embedded systems, smartphones, cloud storage databases, and other modern electronic devices.
Figure 1: Nand-Flash and eMMC chip
Memory Device Lifespan
One of the key challenges when using Nand-Flash is its limited write endurance. The typical block erase life of Nand-Flash is around 100,000 cycles, while eMMC can handle up to 10,000 cycles. This means that repeated writes can eventually lead to wear and failure. In real-world scenarios, unexpected power loss during erase or write operations can cause data corruption or even system crashes. Engineers have often faced situations where critical programs were lost due to sudden power failures, leading to long hours of troubleshooting and potential project delays.
Data Loss and Corruption
When a file system writes data to Nand-Flash, it first reads the existing data from the block, erases it, and then writes the new data back. If the power is interrupted during this process, data may be lost or corrupted. For instance, if the FAT table of a file system is damaged, the entire system might fail to boot, causing serious operational issues.
System Data Protection Strategies
To prevent such issues, both software and hardware measures should be implemented. On the software side, it's recommended to use controlled resets rather than abrupt power-offs. Adding status messages like "System loading completed" or "Data saving completed" can help users understand the system’s state. Implementing wear-leveling algorithms can also extend the lifespan of the Flash by distributing write operations evenly across the memory. Additionally, writing data to a temporary buffer, such as ferroelectric RAM (FRAM), before moving it to the main Flash can reduce wear.
On the hardware side, ensuring stable power supply is crucial. A power-down detection circuit can trigger a safe shutdown when power is lost, preventing data corruption. Adding a UPS (Uninterruptible Power Supply) system, such as one based on supercapacitors, can provide backup power for a short period, allowing the system to save important data and shut down gracefully.
Figure 2: Ferroelectric material non-volatile memory
Designing a reliable UPS circuit involves several considerations. Capacitors must be balanced to avoid overcharging, and a constant current source is needed to ensure full charge. An overvoltage protection circuit helps maintain stability and reduce power consumption. When using high-voltage sources, a boost circuit may be necessary to protect the capacitors from damage.
Figure 3: UPS core circuit based on farad capacitor
During normal operation, the UPS charges through a dedicated charging circuit. In the event of a power failure, the stored energy in the capacitor provides backup power, allowing the system to safely shut down. It's recommended that the UPS can supply at least 10 seconds of power after a shutdown, giving the system enough time to save data and close the file system properly.
Figure 4: Suggests UPS charge and discharge timing
Power-down detection is essential for reliable operation. A comparator circuit can monitor the power supply voltage and trigger a shutdown when it drops below a certain threshold. Using a Zener diode for reference voltage ensures that the comparator continues to function even when external power is lost. This allows the processor to respond in time and manage the shutdown process effectively.
By combining proper software design, robust hardware protection, and intelligent power management, the risks associated with Nand-Flash and eMMC can be significantly reduced, ensuring more reliable and durable storage solutions.