Advanced Power Shield

Power Shield

The Power Shield (PS) function activates when the external voltage drops to a critical level, such as from 3.3V to 2.7V. At this point, the voltage detection circuit inside the SSD controller triggers the power protection mechanism.

When the SSD is operating, and data is temporarily stored in the DRAM (powered by the external power supply), the SSD controller plays a key role during a power-off process. Upon receiving a warning command from the host about an imminent power interruption, the SSD controller acknowledges the signal and begins transferring the temporarily stored data from the DRAM cache to the flash memory. This process safeguards the firmware and user data in the flash memory from damage.

For example, in a SATA SSD, the controller loads mapping tables and initialization commands into the DRAM during normal operation (Figure 1-A). If the supply voltage (VCC) drops below 4V (Figure 1-B), the SSD controller activates the power protection function. During this phase, the controller flushes data from the DRAM cache into the flash memory to secure user data within the limited remaining power window. Simultaneously, the controller halts communication with the host (Figure 1-C) to protect the SSD. At this stage, the host cannot recognize the SSD, and the SSD remains inactive until the voltage stabilizes.

If the voltage drops further to below 2.7V (Figure 1-D), the SSD controller issues a flush command to save the mapping table back into the flash memory system block. During this period, the host still cannot recognize or interact with the SSD. Even after power is restored, the SSD will not function normally until the host performs a power cycle (power OFF/ON) to reset the SSD and resume operation.

During normal SSD operations, data is temporarily stored in the DRAM cache to bridge the performance gap between the host interface and the NAND flash memory. However, unexpected power losses—such as disconnecting the power cable, sudden battery failure, or unplugging the device—can interrupt the flushing process, potentially causing serious device failure. The Power Shield design resolves these risks using a firmware-based protection mechanism that ensures data integrity and device reliability.