DS1284 Datasheet, PDF (2/3 Pages) Dallas Semiconductor – Watchdog Timekeeper Chip

DS1284
PIN DESCRIPTION
X1, X2 - Connections for a standard 32.768 kHz quartz crystal. The internal oscillator circuitry is
designed for operation with a crystal having a specified load capacitance (C_L) of 6 pF. The crystal is
connected directly to the X1 and X2 pins. There is no need for external capacitors or resistors. For more
information on crystal selection and crystal layout considerations, please consult Application Note 58,
“Crystal Considerations with Dallas Real Time Clocks.”
V_BAT - Battery input for any standard 3-volt lithium cell or other energy source. Battery voltage must be
held between 2.4 and 3.7 volts for proper operation. The nominal write-protect trip point voltage at which
access to registers containing time, watchdog, alarm, and RAM information is denied is set by internal
circuitry as 1.26 x V_BAT. A maximum load of 0.5 µA at 25°C in the absence of power should be used to
size the external energy source. The battery should be connected directly to the V_BAT pin. A diode must
not be placed in series with the battery to the V_BAT pin. Furthermore, a diode is not necessary because
reverse charging current protection circuitry is provided internal to the device and has passed the
requirements of Underwriters Laboratories for UL listing. An optional ground pin is provided for
connection to battery negative. This pin should be grounded but can be left floating.
RCLR - The RCLR pin is used to clear (set to logic 1) all 50 bytes of user NV RAM but does not affect
the registers involved with time, alarm, and watchdog functions. In order to clear the RAM, RCLR must
be forced to an input logic 0 (-0. 3 to +0.8 volts) during battery back-up mode when V_CC is not applied.
The RCLR function is designed to be used via human interface (shorting to ground or by switch) and not
be driven with external buffers. This pin is internally pulled up and should be left floating when not in
use.
DS1284Q 28-PIN PLCC WATCHDOG TIMEKEEPER
PKG
DIM
A IN.
MM
B IN.
MM
D IN.
MM
D2 IN.
MM
E IN.
MM
E2 IN.
MM
F IN.
MM
H IN.
MM
28-PIN
MIN MAX
0.300 BSC
7.62
0.442
17.68
0.462
11.73
0.480
12.2
0.500
12.7
0.390
9.91
0.430
10.92
0.090
2.29
0.120
3.05
0.390
9.91
0.430
10.92
0.015
0.38
0.020
0.518
0.100
2.54
0.020
0.518
2 of 3