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DS1744 Datasheet(PDF) 7 Page - Maxim Integrated Products |
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DS1744 Datasheet(HTML) 7 Page - Maxim Integrated Products |
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7 / 16 page  DS1744/DS1744P Y2K-Compliant, Nonvolatile Timekeeping RAMs 7 of 16 DATA-RETENTION MODE The 5V device is fully accessible and data can be written or read only when VCC is greater than VPF. However, when VCC is below the power-fail point, VPF (point at which write protection occurs), the internal clock registers and SRAM are blocked from any access. At this time the power-fail reset-output signal ( RST ) is driven active and remains active until VCC returns to nominal levels. When VCC falls below the battery switch point VSO (battery supply level), device power is switched from the VCC pin to the backup battery. RTC operation and SRAM data are maintained from the battery until VCC is returned to nominal levels. The 3.3V device is fully accessible, and data can be written or read only when VCC is greater than VPF. When VCC falls below VPF access to the device is inhibited. At this time the power-fail reset-output signal ( RST ) is driven active and remains active until VCC returns to nominal levels. If VPF is less than VSO, the device power is switched from VCC to the backup supply (VBAT) when VCC drops below VPF. If VPF is greater than VSO, the device power is switched from VCC to the backup supply (VBAT) when VCC drops below VSO. RTC operation and SRAM data are maintained from the battery until VCC is returned to nominal levels. The RST signal is an open-drain output and requires a pullup. Except for the RST , all control, data, and address signals must be powered down when VCC is powered down. BATTERY LONGEVITY The DS1744 has a lithium power source that is designed to provide energy for clock activity and clock and RAM data retention when the VCC supply is not present. The capability of this internal power supply is sufficient to power the DS1744 continuously for the life of the equipment in which it is installed. For specification purposes, the life expectancy is 10 years at +25 C with the internal clock oscillator running in the absence of VCC power. Each DS1744 is shipped from Maxim with its lithium energy source disconnected, guaranteeing full energy capacity. When VCC is first applied at a level greater than VPF, the lithium energy source is enabled for battery-backup operation. Actual life expectancy of the DS1744 is much longer than 10 years since no lithium battery energy is consumed when VCC is present. BATTERY MONITOR The DS1744 constantly monitors the battery voltage of the internal battery. The battery flag bit (bit 7) of the day register is used to indicate the voltage-level range of the battery. This bit is not writable and should always be a 1 when read. If a 0 is ever present, an exhausted lithium energy source is indicated, and both the contents of the RTC and RAM are questionable. |
Similar Part No. - DS1744_10 |
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Similar Description - DS1744_10 |
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