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BQ4011MA-70 Datasheet(PDF) 2 Page - Texas Instruments |
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BQ4011MA-70 Datasheet(HTML) 2 Page - Texas Instruments |
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2 / 14 page  Functional Description When power is valid, the bq4013/Y operates as a stan- dard CMOS SRAM. During power-down and power-up cycles, the bq4013/Y acts as a nonvolatile memory, auto- matically protecting and preserving the memory con- tents. Power-down/power-up control circuitry constantly moni- tors the VCC supply for a power-fail-detect threshold VPFD. The bq4013 monitors for VPFD = 4.62V typical for use in systems with 5% supply tolerance. The bq4013Y monitors for VPFD = 4.37V typical for use in systems with 10% supply tolerance. When VCC falls below the VPFD threshold, the SRAM au- tomatically write-protects the data. All outputs become high impedance, and all inputs are treated as “don’t care.” If a valid access is in process at the time of power-fail detection, the memory cycle continues to com- pletion. If the memory cycle fails to terminate within time tWPT, write-protection takes place. As VCC falls past VPFD and approaches 3V, the control circuitry switches to the internal lithium backup supply, which provides data retention until valid VCC is applied. When VCC returns to a level above the internal backup cell voltage, the supply is switched back to VCC. After VCC ramps above the VPFD threshold, write-protection continues for a time tCER (120ms maximum) to allow for processor stabilization. Normal memory operation may resume after this time. The internal coin cell used by the bq4013/Y has an ex- tremely long shelf life and provides data retention for more than 10 years in the absence of system power. As shipped from Unitrode, the integral lithium cell of the MA-type module is electrically isolated from the memory. (Self-discharge in this condition is approxi- mately 0.5% per year.) Following the first application of VCC, this isolation is broken, and the lithium backup cell provides data retention on subsequent power-downs. 2 bq4013/Y OE CE BD-42 WE Power Lithium Cell Power-Fail Control 128K x 8 SRAM Block CECON VCC A0–A16 DQ0–DQ7 Block Diagram |
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