DATASHEET
HIGH PERFORMANCE VCXO
Description
The ICS3726-02 is a low cost, low-jitter,
high-performance VCXO designed to replace
expensive discrete VCXOs modules. The ICS3726-02
offers a wid operating frequency range and high power
supply noise rejection. Using ICS’ patented VCXO
techniques, the device accepts an inexpensive external
pullable crystal in the range of 24 to 36 MHz to produce
a VCXO output clock at the same frequency.
The frequency of the on-chip VCXO is adjusted by an
external control voltage input into pin VIN. Because
VIN is a high-impedance input, it can be driven directly
from an PWM RC integrator circuit. Frequency output
increases with VIN voltage input. The usable range of
VIN is 0 to 3.3 V.
This part is ideal for Set-Top Box, multimedia clock
synthesizers and ADSL/VDSL applications.
ICS3726-02
Features
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•
•
•
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Packaged in 8-pin SOIC
Operational frequency range of 24 MHz to 36 MHz
Uses an inexpensive external pullable crystal
On-chip patented VCXO with pull range of ±115 ppm
VCXO tuning voltage of 0 to 3.3 V
Output Enable control
12 mA output drive capability at TTL levels
Advanced, low-power, sub-micron CMOS process
Available in Pb (lead) free package
Block Diagram
VDD
VIN
X1
24 to 36 MHz
Pullable Crystal
X2
Voltage
Controlled
Crystal
Oscillator
24 to 36 MHz
Clock (REFOUT)
Optional tuning
crystal capacitors
GND
OE
IDT™ / ICS™
HIGH PERFORMANCE VCXO
1
ICS3726-02
REV C 030706
ICS3726-02
HIGH PERFORMANCE VCXO
VCXO
External Component Selection
The ICS3726-02 requires a minimum number of
external components for proper operation.
Decoupling Capacitors
A decoupling capacitor of 0.01
µF
should be connected
between VDD and GND on pins 6 and 4 as close to the
ICS3726-02 as possible. For optimum device
performance, the decoupling capacitor should be
mounted on the component side of the PCB. Avoid the
use of vias in the decoupling circuit.
The external crystal must be connected as close to the
chip as possible and should be on the same side of the
PCB as the ICS3726-02. There should be no via’s
between the crystal pins and the X1 and X2 device pins.
There should be no signal traces underneath or close to
the crystal. See application note MAN05.
Crystal Tuning Load Capacitors
The crystal traces should include pads for small fixed
capacitors, one between X1 and ground, and another
between X2 and ground. Stuffing of these capacitors on
the PCB is optional. The need for these capacitors is
determined at system prototype evaluation, and is
influenced by the particular crystal used (manufacture
and frequency) and by PCB layout. The typical required
capacitor value is 1 to 4 pF. This chip has internal load
capacitors and is designed to work with surface mount
crystals with 10 pF load capacitance.
The procedure for determining the value of these
capacitors can be found in application note MAN05.
Series Termination Resistor
When the PCB trace between the clock output and the
load is over 1 inch, series termination should be used.
To series terminate a 50Ω trace (a commonly used
trace impedance), place a 33Ω resistor in series with
the clock line, as close to the clock output pin as
possible. The nominal impedance of the clock output is
20Ω.
Quartz Crystal
The ICS3726-02 VCXO function consists of the
external crystal and the integrated VCXO oscillator
circuit. To assure the best system performance
(frequency pull range) and reliability, a crystal device
with the recommended parameters (shown below) must
be used, and the layout guidelines discussed in the
following section shown must be followed.
The oscillation frequency of a quartz crystal is
determined by its “cut” and by the load capacitors
connected to it. The ICS3726-02 incorporates on-chip
variable load capacitors that pull (change) the
frequency of the crystal. The crystal specified for use
with the ICS3726-02 is designed to have zero frequency
error when the total of on-chip + stray capacitance is 10
pF.
Recommended Crystal Parameters:
Initial Accuracy at 25
°
C
Temperature Stability
Aging
Load Capacitance
Shunt Capacitance, C0
C0/C1 Ratio
Equivalent Series Resistance
±20 ppm
±30 ppm
±20 ppm
14 pF
7 pF max
250 max
35
Ω
max
IDT™ / ICS™
HIGH PERFORMANCE VCXO
3
ICS3726-02
REV C 030706
ICS3726-02
HIGH PERFORMANCE VCXO
VCXO
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the ICS3726-02. These ratings,
which are standard values for ICS commercially rated parts, are stress ratings only. Functional operation of
the device at these or any other conditions above those indicated in the operational sections of the
specifications is not implied. Exposure to absolute maximum rating conditions for extended periods can
affect product reliability. Electrical parameters are guaranteed only over the recommended operating
temperature range.
Item
Supply Voltage, VDD
All Inputs and Outputs
Ambient Operating Temperature
Storage Temperature
Soldering Temperature
7V
Rating
-0.5 V to VDD+0.5 V
0 to +70°C
-65 to +150°C
260°C
Recommended Operation Conditions
Parameter
Ambient Operating Temperature
Power Supply Voltage (measured in respect to GND)
Reference crystal parameters
Min.
0
+3.135
Typ.
–
Max.
+70
+3.465
Units
°C
V
Refer to page 3
IDT™ / ICS™
HIGH PERFORMANCE VCXO
4
ICS3726-02
REV C 030706
ICS3726-02
HIGH PERFORMANCE VCXO
VCXO
DC Electrical Characteristics
VDD=3.3 V ±5%
, Ambient temperature 0 to +70°C, unless stated otherwise
Parameter
Operating Voltage
Output High Voltage
Output Low Voltage
Output High Voltage (CMOS
Level)
Operating Supply Current
Short Circuit Current
VIN, VCXO Control Voltage
Symbol
VDD
V
OH
V
OL
V
OH
IDD
I
OS
V
IA
Conditions
I
OH
= -12 mA
I
OL
= 12 mA
I
OH
= -4 mA
No load
Min.
3.135
2.4
Typ.
Max.
3.465
0.4
Units
V
V
V
V
VDD-0.4
6
±50
0
3.3
mA
mA
V
AC Electrical Characteristics
VDD = 3.3 V ±5%,
Ambient Temperature 0 to +70° C, unless stated otherwise
Parameter
Output Frequency
Crystal Pullability
VCXO Gain
Output Rise Time
Output Fall Time
Output Clock Duty Cycle
Period Jitter RMS
Period Jitter P- P
Integrated Jitter RMS
Phase Noise relative to
Carrier
Symbol
F
O
F
P
t
OR
t
OF
t
D
t
J
t
J
Conditions
0V< VIN < 3.3 V, Note 1
VIN = VDD/2 + 1 V, Note 1
0.8 to 2.0 V, C
L
=15 pF
2.0 to 0.8 V, C
L
=15 pF
Measured at 1.4 V, C
L
=15 pF
C
L
=15 pF @35.328 MHz
C
L
=15 pF@35.328 MHz
Integrated 12 kHz to 20 MHz
@ 35.328 MHz
@35.328 MHz Carrier
frequency
@10 Hz
@100 Hz
@1 kHz
@10 kHz
@100 kHz
@1 MHz
Min.
24
+ 115
Typ.
Max. Units
36
MHz
ppm
ppm/V
1.5
1.5
60
ns
ns
%
ps
ps
ps
150
0.5
0.6
40
50
8
90
1
-60
-88
-117
-135
-150
-145
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
dBc/Hz
Note 1: External crystal device must conform with Pullable Crystal Specifications listed on page 3.
IDT™ / ICS™
HIGH PERFORMANCE VCXO
5
ICS3726-02
REV C 030706
PCB设计
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