Increasing the reliability of solid state drives (SSDs) by operating through brown outs and retaining all data during black outs is paramount. This level of reliability requires a back-up power system to be present in the SSD. This system must store significant energy, while being able to use (discharge) and replenish (recharge) the energy in the storage system.
Capacitors are usually used to store energy due to their wide availability and higher voltage operation. Since the energy amount stored is proportional to the square of the stored voltage (), the required capacitance is less if the voltage is higher. Storing the energy at a higher voltage presents two design challenges: how do you boost the input power to the higher voltage, and how do you efficiently get the stored energy out of the higher voltage?
You’ll need a higher voltage charge and discharge circuit; by combining these two functions into one device, you’ll save cost and space. TI Design, PMP9761, demonstrates a single integrated circuit (IC) SSD back-up power solution, which uses just 600 µF of capacitance to operate for 4.5 msec at 5 W of output power. The TPS63060 buck-boost converter pairs well with the TPS25940A eFuse to operate bi-directionally, charging and discharging the storage capacitors.
After being pre-charged with a simple resistor and diode, the storage capacitors are charged through the TPS63060, which takes its power from the input bus. Due to leakages, the TPS63060 then refreshes the charge on the capacitor bank during normal SSD operation and is always ready to support a loss of input power. When such a loss occurs, the TPS63060 quickly switches to discharge mode and keeps the input voltage bus sufficiently high to power the system. During this discharge time, the TPS25940A eFuse disconnects the input bus from the system to direct all back-up energy to the SSD. The SSD operates for the back-up time, writing its data to memory, and securing an orderly shutdown.
How can this solution benefit your backup power systems?