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FM18L08-70-P データシート(PDF) 4 Page - List of Unclassifed Manufacturers |
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FM18L08-70-P データシート(HTML) 4 Page - List of Unclassifed Manufacturers |
4 / 11 page Ramtron FM18L08 23 March 2001 4/11 access. All memory cycles consist of a memory access and a pre -charge. The pre-charge is user initiated by taking the /CE signal high or inactive. It must remain high for at least the minimum pre-charge timing specification. The user dictates the beginning of this operation since a pre-charge will not begin until /CE rises. However, the device has a maximum /CE low time specification that must be satisfied. Applications As a true nonvolatile RAM, the FM18L08 fits into many diverse applications. Clearly, its monolithic nature and high performance make it superior to battery-backed SRAM in most every application. Unlimited endurance allows the FM18L08 to be used in applications that could not take advantage of the previous generation of RAM products. This applications guide is intended to facilitate the transition from BBSRAM to FRAM. It is divided into two parts. First is a treatment of the advantages of FRAM memory compared with battery-backed SRAM. Second is a design guide, which highlights the simple design considerations that should be reviewed in both retrofit and new design situations. FRAM Advantages Although battery -backed SRAM is a mature and established solution, it has numerous weaknesses. These stem directly or indirectly from the presence of the battery. FRAM uses an inherently nonvolatile storage mechanism that requires no battery. It therefore eliminates these weaknesses. The major considerations in upgrading to FRAM are as follows. Construction Issues 1. Cost The cost of both the component and the manufacturing overhead of battery-backed SRAM is high. FRAM with its monolithic construction is inherently a lower cost solution. In addition, there is no ‘built-in’ rework step required for battery attachment when using surface mount parts. Therefore assembly is streamlined and more cost effective. In the case of DIP battery-backed modules, the user is constrained to through-hole assembly techniques and a board wash using no water. 2. Humidity A typical battery-backed SRAM module is qualified at 60º C, 90% Rh, no bias, and no pressure. This is because the multi-component assemblies are vulnerable to moisture, not to mention dirt. FRAM is qualified using HAST – highly accelerated stress test. This requires 120º C at 85% Rh, 24.4 psia at VDD. 3. System reliability Data integrity must be in question when using a battery-backed SRAM. They are inherently vulnerable to shock and vibration. If the battery contact comes loose, data will be lost. In addition a negative voltage, even a momentary undershoot, on any pin of a battery -backed SRAM can cause data loss. The negative voltage causes current to be drawn directly from the battery. These momentary short circuits can greatly weaken a battery and reduce its capacity over time. In general, there is no way to monitor the lost battery capacity. Should an undershoot occur in a battery backed system during a power down, data can be lost immediately. 4. Space Certain disadvantages of battery -backed SRAM, such as susceptibility to shock, can be reduced by using the old fashioned DIP module. However, this alternative takes up board space, height, and dictates through-hole assembly. FRAM offers a true surface- mount solution that uses 25% of the board space. No multi-piece assemblies, no connectors, and no modules. A real nonvolatile RAM is finally available! Direct Battery Issues 5. Field maintenance Batteries, no matter how mature, are a built-in maintenance problem. They eventually must be replaced. Despite long life projections, it is impossible to know if any individual battery will last considering all of the factors that can degrade them. 6. Environmental Lithium batteries are widely regarded as an environmental problem. They are a potential fire hazard and proper disposal can be a burden. In addition, shipping of lithium batteries may be restricted. 7. Style! Backing up an SRAM with a battery is an old- fashioned approach. In many cases, such modules are the only through-hole component in sight. FRAM is the latest memory technology and it is changing the way systems are designed. |
同様の部品番号 - FM18L08-70-P |
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同様の説明 - FM18L08-70-P |
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