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DS1558Y Datasheet(PDF) 6 Page - Dallas Semiconductor |
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DS1558Y Datasheet(HTML) 6 Page - Dallas Semiconductor |
6 / 18 page DS1558 6 of 18 BATTERY LONGIVITY The battery lifetime is dependent on the RAM battery standby current and the DS1558 internal clock oscillator current. The total battery current is IOSC + ICCO. When VCC is above VPF, IBAT current is less than 50nA. The DS1558 has an internal circuit to prevent battery charging. No external protection components are required, and none should be used. The DS1558 has two battery pins that operate independently; the DS1558 selects the higher of the two inputs. If only one battery is used, the battery should be attached to VBAT1, and VBAT2 should be grounded. INTERNAL BATTERY MONITOR The DS1558 constantly monitors the battery voltage of the internal battery. The battery-low flag (BLF) bit of the flags register (B4 of 7FFF0h) is not writable and should always be a 0 when read. If a 1 is ever present, both battery inputs are below 1.8V and both the contents of the RTC and RAM are questionable. POWER-ON RESET A temperature-compensated comparator circuit monitors the level of VCC. When VCC falls to the power- fail trip point, the RST signal (open drain) is pulled low. When VCC returns to nominal levels, the RST signal continues to be pulled low for a period of 40ms to 200ms. The power-on reset function is independent of the RTC oscillator and thus is operational whether or not the oscillator is enabled. |
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