ICS840-77 Datasheet, PDF (6/9 Pages) Integrated Circuit Systems – 77.76MHZ, LVCMOS/LVTTL OSCILLATOR REPLACEMENT

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS840-77
77.76MHZ, LVCMOS/LVTTL
OSCILLATOR REPLACEMENT
APPLICATION INFORMATION
RECOMMENDATIONS FOR UNUSED INPUT AND OUTPUT PINS
INPUTS:
CRYSTAL INPUT:
For applications not requiring the use of the crystal oscillator
input, both XTAL_IN and XTAL_OUT can be left floating. Though
not required, but for additional protection, a 1kΩ resistor can be
tied from XTAL_IN to ground.
OUTPUTS:
LVCMOS OUTPUT:
All unused LVCMOS output can be left floating. We recommend
that there is no trace attached.
SELECT PINS:
All select pins have internal pull-ups and pull-downs; additional
resistance is not required but can be added for additional
protection. A 1kΩ resistor can be used.
CRYSTAL INPUT INTERFACE
The ICS840-77 has been characterized with 18pF parallel
resonant crystals. The capacitor values, C1 and C2, shown in
Figure 1 below were determined using a 19.44MHz, 18pF paral-
lel resonant crystal and were chosen to minimize the ppm error.
The optimum C1 and C2 values can be slightly adjusted for
different board layouts.
X1
18pF Parallel Cry stal
XTAL_OUT
C1
12p
XTAL_IN
C2
12p
Figure 1. CRYSTAL INPUt INTERFACE
840AG-77
www.icst.com/products/hiperclocks.html
6
REV. A NOVEMBER 7, 2005