Introduction Xicor's NOVRAM (Nonvolatile RAM) devices highspeed SRAMs

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Introduction Xicor's NOVRAM (Nonvolatile RAM) devices highspeed SRAMs

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NOVRAM AUTOSTORE Considerations
Introduction Xicor's NOVRAM (Nonvolatile RAM) devices highspeed SRAMs overlaid bit-for-bit with nonvolatile E2PROM array. AUTOSTORE (AS) feature available these parts automatically saves contents E2PROM during power-down. typically requires some basic holdup circuitry ensure successful completion. Basic Autostore Circuit minimal components necessary achieve capacitor diode which connect NOVRAM shown Figure "hold-up" capacitor must capable supplying maximum current (ICC3 max.) maximum period (TASTO max.) falls level between threshold voltage (VASTH min.) voltage (VASEND min.). "hold-up" capacitor value (CH) calculated using equation: ASTO ASTH ASEND Table NOVRAM AUTOSTORE Device Summary VASTH Part X24C45 X20C16 VASEND TASTO (ms) ICC3 (mA) derived taking integral
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circuit with supply requires that diode have forward voltage drop Schottky diode such 1N5817 (available from Motorola Philips) suitable with maximum 0.32V 100mA. cost component around volume. Power Supply Limitation Xicor specifies NOVRAM operating range between 4.5V 5.5V. diode circuit, however, results voltage drop (VF) between power supply NOVRAM's pin. maximum 0.32V results possible supply voltage 4.62V. reasonable margin safety, suggested circuit should powered using supply that operates above 4.75V. ±5%. power supply would ensuring correct operation.
(µF)
Figure
Figure
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Xicor Pre-AUTOSTORE Data Corruption supply microcontroller interfacing parallel NOVRAM lost while NOVRAM remains powered, inadvertent writes SRAM occur. uncertain state microcontroller control lines during power-down cause fluctuations status which result write condition. Invalid SRAM data transferred nonvolatile E2PROM array these changes occur before These inadvertent write conditions avoided using supervisory available from manufacturers such Linear Technology Maxim. These devices control NOVRAM that below supply threshold voltage, held HIGH NOVRAM placed into standby condition. example such circuit shown Figure
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Conclusion NOVRAMs combine advantages fast access RAMs nonvolatility E2PROMs. AUTOSTORE feature enables data integrity maintained during power-down. most applications additional components diode capacitor) that needed ensure successful completion AUTOSTORE. supervisory also useful protect part from inadvertent writes.
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Introduction Xicor's NOVRAM (Nonvolatile RAM) devices highspeed SRAMs

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