Solution for Reliable Interim Power Supply in Solid State Drives (Ssds)

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Murata Supercapacitor Application Note No. C2M1CXS-074B Hand RoHS REACH Soldering Supercapacitor (EDLC) solution for Only Reliable Interim Power supply in Solid State Drives (SSDs)

1. Interim power supply in SSDs large energy requirement because supercapacitor has quite 1.1. Background larger energy per one piece compared with other capacitors (Fig. 2) 1). However it has disadvantages in the life. In general Solid State Drives (SSDs) are growing in the storage supercapacitor has dry out failure and aging degradation. market for both of enterprise and consumer. One of the Murata’s SSD-specific supercapacitor DMT series was reasons is that the processing speed during writing/reading is improved in such supercapacitors disadvantages (see section quite faster than HDDs. Another reason is that the power 2.1). consumption is lower due to no mechanical movement like hard disk. Therefore SSD users can receive benefits of Table 1 Advantage/disadvantage in each solution high-speed and low electricity cost. However when power interruption happens in SSDs or SSD Advantage Disadvantage system is shut down by incorrect way, the system fails to  Quite small energy prepare standby mode or the cache memory disappears. In Al caps  Totally cheap  Large dimensions order to avoid these problems, some high-class or  Limited life (dry out) middle-class SSDs have interim power supply (backup function) in the circuit (Fig. 1).  Need multiple pieces  Larger energy  Short circuit failure Ta caps than Al cap Power interruption  Low safety (ignition)  Good life Power line X Buck/Boost DRAM  Totally expensive  Quite large  Limited life (dry out, Buck Flash Memory Supercaps energy (Fig. 2) aging) Capacitor for interim power supply Buck Controller × 100 ×12 Tantalum capacitor Fig. 1 Interim power supply in SSD 6.3V 1,500uF Aluminum capacitor 7.3 x 6.0 x 2mm 16V 2,200uF (20 mJ) Φ10mmx20mm (160 mJ) DMT334R2S474M3DTA0 DMT334R2S474M3DTA0 1.2. Solutions for interim power supply 4.2V 470mF 4.2V 470mF 14 x 21 x 3.5mm 14 x 21 x 3.5mm (2,000 mJ @ 50˚C 5years) There are some solutions for interim power supply with (2,000 mJ @ 50˚C 5years) using aluminum capacitor, tantalum capacitor and Fig. 2 Quite large energy of Murata’s supercapacitors1) supercapacitor (EDLC). Each solution has both of advantage and disadvantage (Table 1). Aluminum capacitor solution is the cheapest one but the 2. Murata supercapacitor solution for reliable interim energy will be quite small and cannot realize small and slim power supply circuit design. In addition, aluminum capacitor has limited life 2.1. SSD-specific supercapacitor; DMT series due to dry out. Murata’s DMT series is a group of supercapacitors specially Tantalum capacitor solution can gain efficiently larger designed for SSD application (Table 2). Disadvantages and energy than aluminum capacitor solution because it has larger concerns (dry out failure and aging degradation) that energy density because of material technology (good CV conventional supercapacitors have were improved by Murata value by fine powder technology). Moreover it has also good technology. life. However multiple pieces of expensive tantalum capacitor Dry out is caused by electrolyte evaporation from inside to are needed when large energy is required. Therefore total cost outside via sealing part. DMT has high boiling-temperature will be higher. In addition, tantalum capacitor has concerns electrolyte that does not easily evaporate even under high about short circuit failure and ignition. Therefore SSD temperature condition2). And also sealing part of Murata’s designers have to consider use condition more closely. supercapacitors is designed quite small to avoid evaporation2). Supercapacitor solution is the best solution in the case of Dry out failure will not happen even 5 years later at 85°C2).

Aging degradation is caused by moisture from outside. designers may be able to spend such space or cost for other Murata supercapacitors’ quite thin sealing part can also components like DRAM, flash memory and so on. From those prevent moisture from entering inside and reduce aging benefits, DMT is actually used in several enterprise SSDs in compared with conventional supercapacitors (Fig. 3) 2). the market. Murata has acceleration factors in voltage and temperature In addition, Murata can calculate performance of involved with aging speed from several acceleration tests and supercapacitors from acceleration factors in case they are can support calculation of aging degradation in case of various used for long term. conditions2).  Large-energy interim power supply (backup) into  Quite larger energy than Tantalum capacitors small and slim design than other capacitors  Excellent durability to dry out  Reduction in mounting space or cost  Improved aging  Technical support from Murata about  Wealth of reliability test data and predictable performance calculation for long term use performance for long-term use 2.3. Large-energy interim power supply of Murata

Table 2 Murata’s supercapacitor for SSD supercapacitors Operating Rated Cap. ESR L x W t Series Part Number Temp. Voltage [mF] [mohm] [mm] [mm] (°C) Fig. 4 is an example how to use DMT for SSD backup. One 2.2 DMT3N4R2U224M3DTA0 220 300 21 x 14 piece of DMT334R2S474M3DTA0 is used with charged at 4.2 (2.5Max) DMT 4.2V -40 to 85 3.5 V. Buck/boost converter is put between loads (DRAM, flash DMT334R2S474M3DTA0 470 130 21 x 14 (3.8Max) memory or controller) and supercapacitor for providing stable

voltage power because supercapacitor voltage changes with charge and discharge. In case of power interruption, 14 supercapacitor discharges to the loads with constant power

4 21 (**W). Buck/boost converter can work by supercapacitor until supercapacitor voltage reaches the converter’s rated minimum **mm input voltage (**ms). Those power and backup time depends

on available energy of supercapacitor related to capacitance 100% and ESR. 90% 80% The available backup time at 5 years later in several 70% muRata discharge power in the case of Fig. 4 is shown in Table 3. 60% 50% When the circumstance temperature is 50°C, it is calculated to 40% Cylinder be 1,000ms in 1W, 270ms in 3W and 130ms in 5W. It will be 30%

20% 18ms in 5W even at 70°C. Capacitance Capacitance (100mA)ratio 10% When larger energy is required, there are several solutions 0% 0 500 1000 1500 2000 2500 3000 such as high-voltage charge by series connection of multiple Time [hours] DMTs, high capacitance by parallel connection of multiple Fig. 3 Improved aging of Murata’s supercapacitor compared DMTs, derating and so on. Please contact Murata for the best solution in your condition. with conventional supercapacitor (Cylinder type) In the case of using DMT, balance resistances should be 2.2. Customers’ benefits used in order to keep good voltage balance between two Features of Murata’s DMT series are quite larger energy capacitors (DMT has two capacitors in series per one product. than aluminum capacitors or tantalum capacitors. And also it Recommendation value is 1 kΩ/each). has higher power, lower profile and higher reliability than conventional supercapacitors. Therefore SSD designers can receive a benefit of large-energy interim power supply into small and slim design. Such benefit gives possibility to reduce PCB space or cost and

Power **W **ms 4.2V 3.3V line Buck Buck DRAM Boost

1 kΩ

Buck Flash Memory 1 kΩ

DMT334R2S474M3DTA0 (2 series cap in 1 package) Balance Controller Resistance Buck

Fig. 4 Example of use condition

Table 3 Available backup time calculation in several discharge power 5 years later (P/N: DMT334R2S474M3DTA0) Use condition

50°C 5years 60°C 5years 70°C 5years

1W*1,000ms 1W*600ms 1W*250ms

3W*270ms 3W*150ms 3W*50ms 5W*130ms 5W*70ms 5W*18ms

2.4. Technical support for customers Murata can offer technical supports for your electrical design and mechanical design. Especially Murata can support in calculation of capacitance/ ESR change during long term use in your condition (voltage and temperature) and available energy in your power condition (discharge behavior at any wattage).

3. Reference documents 1) C2M1CXS-053 Murata supercapacitor Technical Note 2) C2M1CXS-068 Murata Supercapacitor Reliability Data Book (DMT Series, B) 3) Web site http://www.murata.com/en-global/products/ capacitor/edlc