DS1284 datasheet(2/3 Pages) DALLAS

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DS1284

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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 (CL) 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.”

VBAT - 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 VBAT. 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 VBAT pin. A diode must

not be placed in series with the battery to the VBAT 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 VCC 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

28-PIN

DIM

MIN

MAX

A IN.

0.300 BSC

7.62

B IN.

0.442

17.68

0.462

11.73

D IN.

0.480

12.2

0.500

12.7

D2 IN.

0.390

9.91

0.430

10.92

E IN.

0.090

2.29

0.120

3.05

E2 IN.

0.390

9.91

0.430

10.92

F IN.

0.015

0.38

0.020

0.518

H IN.

0.100

2.54

0.020

0.518

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