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M48Z58Y-70PC1 Datasheet(PDF) 9 Page - STMicroelectronics |
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M48Z58Y-70PC1 Datasheet(HTML) 9 Page - STMicroelectronics |
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9 / 17 page  DATA RETENTION MODE With valid VCC applied, the M48Z58/58Y operates as a conventional BYTEWIDE ™ static RAM. Should the supply voltage decay, the RAM will automatically power-fail deselect, write protecting itself when VCC f alls within the VPFD(max), VPFD(min) window. All outputs become high imped- ance, and all inputs are treated as "don’t care." Note: A power failure during a write cycle may corrupt data at the currently addressed location, but does not jeopardize the rest of the RAM’s content. At voltages below VPFD(min), the user can be assured the memory will be in a write protected state, provided the VCC fall time is not less than tF. The M48Z58/58Y may respond to transient noise spikes on VCC that reach into the deselect window during the time the device is sampling VCC. There- fore, decoupling of the power supply lines is rec- ommended. When VCC drops below VSO, the control circuit switches power to the internal battery which pre- serves data. The internal button cell will maintain data in the M48Z58/58Y for an accumulated period of at least 10 years when VCC is less than VSO. As system power returns and VCC rises above VSO, the battery is disconnected, and the power supply is switched to external VCC. Write protection con- tinues until VCC reaches VPFD(min) plus tREC(min). Normal RAM operation can resume tREC after VCC exceeds VPFD(max). For more information on Battery Storage Life refer to the Application Note AN1012. POWER SUPPLY DECOUPLING and UNDER- SHOOT PROTECTION ICC transients, including those produced by output switching, can produce voltage fluctuations, result- ing in spikes on the VCC bus. These transients can be reduced if capacitors are used to store energy, which stabilizes the VCC bus. The energy stored in the bypass capacitors will be released as low going spikes are generated or energy will be absorbed when overshoots occur. A ceramic bypass capaci- tor value of 0.1 µF (as shown in Figure 9) is recom- mended in order to provide the needed filtering. In addition to transients that are caused by normal SRAM operation, power cycling can generate negative voltage spikes on VCC that drive it to values below VSS by as much as one Volt. These negative spikes can cause data corruption in the SRAM while in battery backup mode. To protect from these voltage spikes, it is recommeded to connect a schottky diode from VCC to VSS (cathode connected to VCC, anode to VSS). Schottky diode 1N5817 is recommended for through hole and MBRS120T3 is recommended for surface mount. AI02169 VCC 0.1 µF DEVICE VCC VSS Figure 9. Supply Voltage Protection 9/17 M48Z58, M48Z58Y |
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