PRELIMINARY
Integrated
Circuit
Systems, Inc.
ICS840-77
77.76MH
Z
, LVCMOS/LVTTL
O
SCILLATOR
R
EPLACEMENT
A
PPLICATION
I
NFORMATION
R
ECOMMENDATIONS FOR
U
NUSED
I
NPUT
I
NPUTS
:
AND
O
UTPUT
P
INS
O
UTPUTS
:
LVCMOS O
UTPUT
:
All unused LVCMOS output can be left floating. We recommend
that there is no trace attached.
C
RYSTAL
I
NPUT
:
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.
S
ELECT
P
INS
:
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.
C
RYSTAL
I
NPUT
I
NTERFACE
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.
XTAL_OUT
C1
12p
X1
18pF Parallel Cry stal
XTAL_IN
C2
12p
Figure 1. C
RYSTAL
I
NPU
t I
NTERFACE
840AG-77
www.icst.com/products/hiperclocks.html
6
REV. A NOVEMBER 7, 2005
ICS [ INTEGRATED CIRCUIT SYSTEMS ]
