DS1689 datasheet(3/32 Pages) DALLAS

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DS1689/DS1693

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VCCO (External SRAM Power Supply Output) - This pin will be internally connected to VCCI when

VCCI is within nominal limits. However, during power fail, VCCO will be internally connected to the VBAT

or VBAUX (whichever is larger). For 5-volt operation, switch over from VCCI to the backup supply occurs

when VCCI drops below the larger of VBAT and VBAUX. For 3-volt operation, switch over from VCCI to the

backup supply occurs at VPF if VPF is less than VBAT and VBAUX. If VPF is greater than VBAT and VBAUX,

the switch from VCCI to the backup supply occurs when VCCI drops below the larger of VBAT and VBAUX.

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 VCC is above VPF. A 32 kHz square wave is also available when

VCC is less than VPF if E32K=1, ABE=1, and voltage is applied to VBAUX.

DS1689 Datasheet(PDF) 3 Page - Dallas Semiconductor