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M48Z512A-70PM9 Datasheet(PDF) 11 Page - STMicroelectronics |
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M48Z512A-70PM9 Datasheet(HTML) 11 Page - STMicroelectronics |
11 / 17 page 11/17 M48Z512A, M48Z512AY Figure 11. Supply Voltage Protection AI02169 VCC 0.1 µF DEVICE VCC VSS DATA RETENTION MODE With valid VCC applied, the M48Z512A/512AY op- erates as a conventional BYTEWIDE ™ static RAM. Should the supply voltage decay, the RAM will automatically power-fail deselect, write pro- tecting itself tWP after VCC falls below VPFD.All outputs become high impedance, and all inputs are treated as ”don’t care.” If power fail detection occurs during a valid ac- cess, the memory cycle continues to completion. If the memory cycle fails to terminate within the time tWP, write protection takes place. When VCC drops below VSO, the control circuit switches power to the internal energy source which preserves data. The internal coin cell will maintain data in the M48Z512A/512AY after the initial application of VCC for an accumulated period of at least 10 years when VCC is less than VSO. As system power re- turns and VCC rises above VSO, the battery is dis- connected, and the power supply is switched to external VCC. Write protection continues for tER af- ter VCC reaches VPFD to allow for processor stabi- lization. After tER, normal RAM operation can resume. For more information on Battery Storage Life refer to the Application Note AN1012. POWER SUPPLY DECOUPLING and UNDERSHOOT PROTECTION ICC transients, including those produced by output switching, can produce voltage fluctuations, re- sulting in spikes on the VCC bus. These transients can be reduced if capacitors are used to store en- ergy, 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 by- pass capacitor value of 0.1 µF (as shown in Figure 11) is recommended in order to provide the need- ed filtering. In addition to transients that are caused by normal SRAM operation, power cycling can generate neg- ative voltage spikes on VCC that drive it to values below VSS by as much as one Volt. These nega- tive 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 con- nected to VCC, anode to VSS). Schottky diode 1N5817 is recommended for through hole and MBRS120T3 is recommended for surface mount. |
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