DS1689 datasheet(5/32 Pages) DALLAS

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DS1689/DS1693

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(Kickstart Input; active low) - When VCC is removed from the DS1689/DS1693, the system can be

powered on in response to an active low transition on the KS pin, as might be generated from a key

closure. VBAUX must be present and Auxiliary Battery Enable bit (ABE) must be set to 1 if the kickstart

function is used, and the KS pin must be pulled up to the VBAUX supply. While VCC is applied, the KS pin

can be used as an interrupt input.

RCLR

(RAM Clear Input; active low) - If enabled by software, taking RCLR low will result in the

clearing of the 114 bytes of user RAM. When enabled, RCLR can be activated whether or not VCC is

present.

VBAUX - Auxiliary battery input required for kickstart and wake-up features. This input also supports

clock/calendar and External NVRAM if VBAT is at lower voltage or is not present. A standard +3-volt

lithium cell or other energy source can be used. Battery voltage must be held between +2.5 and +3.7 volts

for proper operation. If VBAUX is not going to be used it should be grounded and auxiliary battery enable

bit bank 1, register 4BH, should=0.

DS1689 ONLY

X1, X2 - Connections for a standard 32.768 kHz quartz crystal. For greatest accuracy, the DS1689 must

be used with a crystal that has a specified load capacitance of either 6 pF or 12.5 pF. The Crystal Select

(CS) bit in Extended Control Register 4B is used to select operation with a 6 pF or 12.5 pF crystal. The

crystal is attached directly to the X1 and X2 pins. There is no need for external capacitors or resistors.

Note: X1 and X2 are very high impedance nodes. It is recommended that they and the crystal by guard-

ringed with ground and that high frequency signals be kept away from the crystal area.

For more information on crystal selection and crystal layout considerations, please consult Application

Note 58, “Crystal Considerations with Dallas Real Time Clocks.” The DS1689 can also be driven by an

external 32.768 kHz oscillator. In this configuration, the X1 pin is connected to the external oscillator

signal and the X2 pin is floated.

VBAT - Battery input for any standard 3-Volt lithium cell or other energy source. Battery voltage must be

held between 2.5 and 3.7 volts for proper operation.

POWER-DOWN/POWER-UP CONSIDERATIONS

The real-time clock function will continue to operate and all of the RAM, time, calendar, and alarm

memory locations remain nonvolatile regardless of the level of the VCCI input. When VCCI is applied to

the DS1689/DS1693 and reaches a level of greater than VPF (power fail trip point), the device becomes

accessible after tREC, provided that the oscillator is running and the oscillator countdown chain is not in

reset (see Register A). This time period allows the system to stabilize after power is applied.

When PSEL is floating or logic 0, the DS1689 is in autosense mode and 3-volt or 5-volt operation is

determined based on the voltage on VCCI. Selection of 5-volt operation is automatically invoked when

VCCI rises above 4.5 volts for a minimum of tREC. However, 3-volt operation is automatically selected if

VCCI does not rise above the level of 4.25 volts. Selection of the power supply input levels requires

150 ms of input stability before operation can commence.

DS1689 Datasheet(PDF) 5 Page - Dallas Semiconductor