DS17885 Dallas, DS17885 Datasheet - Page 6

• Manufacturer Part Number: DS17885
• Description: (DS17886 / DS17887) 3V/5V Real-Time Clock
• Manufacturer: Dallas

DS17885 ONLY
X1, X2 – Connections for a standard 32.768kHz quartz crystal. For greatest accuracy, the DS17885 must
be used with a crystal that has a specified load capacitance of either 6pF or 12.5pF. The crystal select
(CS) bit in extended-control register 4B is used to select operation with a 6pF or 12.5pF 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 be guard-
ringed with ground and that high frequency signals be kept away from the crystal area.
For more information about crystal selection and crystal layout considerations, refer to Application Note
58, “Crystal Considerations with Dallas Real-Time Clocks.” The DS17885 can also be driven by an
external 32.768kHz oscillator. In this configuration, the X1 pin is connected to the external oscillator
signal and the X2 pin is floated.
V
held between 2.5V and 3.7V for proper operation. UL recognized to ensure against reverse charging
current when used in conjunction with a lithium battery. See “Conditions of Acceptability” at
www.maxim-ic.com/TechSupport/AQ/ntrl.htm.
POWER-DOWN/POWER-UP CONSIDERATIONS
The RTC function continues to operate and all of the RAM, time, calendar, and alarm memory locations
remain nonvolatile regardless of the level of the V
DS17885/DS17887 and reaches a level of greater than V
accessible after t
reset (Register A). This time period allows the system to stabilize after power is applied.
The DS17885/DS17887 is available in either a 3V or a 5V device.
The 5V device is fully accessible and data can be written and read only when V
When V
unaffected by the lower input voltage. As V
timekeeper are switched over to a lithium battery connected either to the V
The 3V device is fully accessible and data can be written or read only when V
When V
power supply is switched from V
below V
supply when V
When V
RCLR
BAT
– Battery input for any standard 3V lithium cell or other energy source. Battery voltage must be
, and SQW pins, all inputs are ignored and all outputs are in a high-impedance state.
PF
CC
CC
CC
. If V
is below 4.5V, read and writes are inhibited. However, the timekeeping function continues
falls below V
falls below V
CC
PF
REC
drops below the larger of V
is greater than V
, provided that the oscillator is running and the oscillator countdown chain is not in
PF
PF
, access to the device is inhibited. If V
, the chip is write-protected. With the possible exception of the
CC
BAT
to the backup supply (the greater of
and V
CC
BAT
BAUX
falls below the greater of V
and V
, the power supply is switched from V
6 of 38
BAUX
PF
.
CC
(power-fail trip point), the device becomes
input. When V
PF
is less than V
VBAT
BAT
BAT
and V
pin or V
and V
CC
CC
CC
BAUX
is greater than 2.7V.
is greater than 4.5V.
BAT
BAUX
is applied to the
BAUX
) when V
CC
and V
, the RAM and
pin.
to the backup
KS
BAUX
CC
,
drops
PWR
, the
,