fs6128-01 ETC-unknow, fs6128-01 Datasheet - Page 2

• Manufacturer Part Number: fs6128-01
• Description: Clock Generator With Vcxo
• Manufacturer: ETC-unknow

ISO9001
ISO9001
ISO9001
ISO9001
FS6128-01
FS6128-01
FS6128-01
FS6128-01
PLL Clock Generator IC with VCXO
PLL Clock Generator IC with VCXO
PLL Clock Generator IC with VCXO
PLL Clock Generator IC with VCXO
Table 2: Pin Descriptions
Key: AI = Analog Input; AO = Analog Output; DI = Digital Input; DI
DO = Digital Output; P = Power/Ground; # = Active Low pin
3.0
3.1
The on-chip PLL is a standard frequency- and phase-
locked loop architecture. The PLL multiplies the reference
oscillator to the desired frequency by a ratio of integers.
The frequency multiplication is exact with a zero synthe-
sis error.
3.2
The VCXO provides a tunable, low-jitter frequency refer-
ence for the rest of the FS6128 system components.
Loading capacitance for the crystal is internal to the
FS6128. No external components (other than the reso-
nator itself) are required for operation of the VCXO.
Continuous fine-tuning of the VCXO frequency is accom-
plished by varying the voltage on the XTUNE pin. The
value of this voltage controls the effective capacitance
presented by the VCXO to the crystal.
When using a crystal with a VCXO, it is important that the
crystal load capacitance (as specified in Table 4: Oper-
ating Conditions be matched to the load capacitance as
presented by the VCXO. The crystal must be specified
with the correct load capacitance to obtain the maximum
tuning range.
PIN
1
2
3
4
5
6
7
8
Functional Block Description
Oscillator (VCXO)
Phase-Locked Loop (PLL)
Voltage-Controlled Crystal
TYPE
DO
DO
AO
AI
AI
P
P
-
XTUNE
NAME
XOUT
VDD
VSS
VSS
CLK
XIN
n/c
U
= Input with Internal Pull-Up; DI
VCXO Feedback
Power Supply (+3.3V)
VCXO Tune
Ground
Clock Output
No Connection
Ground
VCXO Drive
2
The oscillator operates the crystal resonator in the paral-
lel-resonant mode. Crystal warping, or the “pulling” of the
crystal oscillation frequency, is accomplished by altering
the effective load capacitance presented to the crystal by
the oscillator circuit. The actual amount that changing the
load capacitance alters the oscillator frequency will be
dependent on the characteristics of the crystal as well as
the oscillator circuit itself.
Specifically, the motional capacitance of the crystal (usu-
ally referred to by crystal manufacturers as C
capacitance of the crystal (C
(C
the crystal in the oscillator circuit.
A simple formula to obtain the warping capability of a
crystal oscillator is:
where C
load capacitance.
EXAMPLE: A crystal with the following parameters is
used. With C
=35pF, the coarse tuning range is
D
= Input with Internal Pull-Down; DIO = Digital Input/Output; DI-3 = Three-Level Digital Input,
L
) of the oscillator determine the warping capability of
L1
f
f
(
and C
ppm
1
DESCRIPTION
0
2
= 0.02pF, C
.
02
)
L2
5
are the two extremes of the applied
2
35
35
C
C
1
AMERICAN MICROSYSTEMS, INC.
13
0
0
= 5pF, C
0
5
), and the load capacitance
C
C
L
10 6
13
2
L
2
C
L1
L
305
1
C
= 13pF, and C
0
10
ppm
C
1
6
), the static
L
April 2000
1
.
4.24.00
L2