DS17487-5+ Maxim Integrated Products, DS17487-5+ Datasheet - Page 11

• Manufacturer Part Number: DS17487-5+
• Description: IC RTC 5V 4K NV RAM 24-EDIP
• Manufacturer: Maxim Integrated Products
• Type: Clock/Calendar/NVSRAMr

Specifications of DS17487-5+

• Memory Size: 32K (4K x 8)
• Time Format: HH:MM:SS (12/24 hr)
• Date Format: YY-MM-DD-dd
• Interface: Parallel
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Package / Case: 24-DIP (600 mil) Module
• Function: Clock/Calendar/Alarm
• Rtc Memory Size: 4096 Byte
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 4.5 V
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Rtc Bus Interface: Multiplexed
• Supply Current: 25 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The DS17x85 is a successor to the DS1285 real-time
clock (RTC). The device provides 18 bytes of real-time
clock/calendar, alarm, and control/status registers and
114 bytes of nonvolatile battery-backed RAM. The
device also provides additional extended RAM in either
2k/4k/8kbytes (DS17285/DS17485/DS17885). A time-
of-day alarm, six maskable interrupts with a common
interrupt output, and a programmable square-wave
output are available. It also operates in either 24-hour
or 12-hour format with an AM/PM indicator. A precision
temperature-compensated circuit monitors the status of
V
device automatically switches to a backup supply. The
backup supply input supports a primary battery, such
as a lithium coin cell. The device is accessed by a mul-
tiplexed address/data bus.
The DS17x85 uses an external 32.768kHz crystal. The
oscillator circuit does not require any external resistors
or capacitors to operate. Table 1 specifies several
crystal parameters for the external crystal, and Figure 2
shows a functional schematic of the oscillator circuit.
The oscillator is controlled by an enable bit in the con-
trol register. Oscillator startup times are highly depen-
dent upon crystal characteristics, PC board leakage,
and layout. High ESR and excessive capacitive loads
are the major contributors to long startup times. A cir-
cuit using a crystal with the recommended characteris-
tics and proper layout usually starts within one second.
An external 32.768kHz oscillator can also drive the
DS17x85. In this configuration, the X1 pin is connected
to the external oscillator signal and the X2 pin is left
unconnected.
The accuracy of the clock is dependent upon the accu-
racy of the crystal and the accuracy of the match
between the capacitive load of the oscillator circuit and
the capacitive load for which the crystal was trimmed.
Additional error will be added by crystal frequency drift
caused by temperature shifts. External circuit noise
coupled into the oscillator circuit may result in the clock
running fast. Figure 3 shows a typical PC board layout
for isolation of the crystal and oscillator from noise.
Refer to Application Note 58: Crystal Considerations
with Dallas Real-Time Clocks for detailed information.
The encapsulated DIP (EDIP) modules are trimmed at
the factory to ±1 minute per month accuracy at 25°C.
CC
. If a primary power-supply failure is detected, the
Clock Accuracy (DS17287,
Detailed Description
DS17487, and DS17887)
Oscillator Circuit
Clock Accuracy
____________________________________________________________________
Table 1. Crystal Specifications* (DS17x85
Only)
* The crystal, traces, and crystal input pins should be isolated
from RF generating signals. Refer to Application Note 58:
Crystal Considerations for Dallas Real-Time Clocks for addi-
tional specifications.
Figure 2. Oscillator Circuit Showing Internal Bias Network
Figure 3. Layout Example
Nominal
Series
Resistance
Load
Capacitance
PARAMETER
LOCAL GROUND PLANE (TOP LAYER)
NOTE: AVOID ROUTING SIGNAL LINES
IN THE CROSSHATCHED AREA
(UPPER LEFT QUADRANT) OF
THE PACKAGE UNLESS THERE IS
A GROUND PLANE BETWEEN THE
SIGNAL LINE AND THE DEVICE PACKAGE.
C
L
1
Real-Time Clocks
CRYSTAL
X1
CRYSTAL
SYMBOL
ESR
C
f
O
L
X2
MIN
C
L
2
32.768
DS17285/87
DS17485/87
DS17885/87
TYP
12.5
6 or
RTC REGISTERS
COUNTDOWN
GND
X1
X2
CHAIN
MAX
50
UNITS
kHz
kΩ
pF
11