DS1689 Datasheet, PDF (3/32 Pages) Dallas Semiconductor – 3-Volt/5-Volt Serialized Real-Time Clock with NV RAM Control

DS1689/DS1693
V_CCO (External SRAM Power Supply Output) - This pin will be internally connected to V_CCI when
V_CCI is within nominal limits. However, during power fail, V_CCO will be internally connected to the V_BAT
or V_BAUX (whichever is larger). For 5-volt operation, switch over from V_CCI to the backup supply occurs
when V_CCI drops below the larger of V_BAT and V_BAUX. For 3-volt operation, switch over from V_CCI to the
backup supply occurs at V_PF if V_PF is less than V_BAT and V_BAUX. If V_PF is greater than V_BAT and V_BAUX,
the switch from V_CCI to the backup supply occurs when V_CCI drops below the larger of V_BAT and V_BAUX.
DS1689/DS1693 BLOCK DIAGRAM Figure 1
SQW (Square Wave Output) - The SQW pin can output a signal from one of 13 taps provided by the 15
internal divider stages of the real time clock. The frequency of the SQW pin can be changed by
programming Register A as shown in Table 2. The SQW signal can be turned on and off using the SQWE
bit in Register B. A 32 kHz SQW signal is output when SQWE=1, the Enable 32 kHz (E32K) bit in
extended register 04BH is a logic 1, and V_CC is above V_PF. A 32 kHz square wave is also available when
V_CC is less than V_PF if E32K=1, ABE=1, and voltage is applied to V_BAUX.
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