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M48Z32V Datasheet(PDF) 8 Page - STMicroelectronics |
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M48Z32V Datasheet(HTML) 8 Page - STMicroelectronics |
8 / 16 page M48Z32V 8/16 Data Retention Mode With valid VCC applied, the M48Z32V operates as a conventional BYTEWIDE™ static RAM. Should the supply voltage decay, the RAM will automati- cally power-fail deselect, write protecting itself when VCC falls within the VPFD (max), VPFD (min) window. All outputs become high impedance, 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 con- tent. 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 M48Z32V 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 external battery which pre- serves data. As system power returns and VCC rises above VSO, the battery is disconnected, and the power supply is switched to external VCC. Write protec- tion continues 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. VCC Noise And Negative Going Transients 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 0.1µF (see Figure 8) is rec- ommended in order to provide the needed 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 negative spikes can cause data corruption in the SRAM while in battery backup mode. To protect from these voltage spikes, ST recommends connecting 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). Figure 8. Supply Voltage Protection AI02169 VCC 0.1 µF DEVICE VCC VSS |
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