DATASHEET
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
Description
The MK3721 series of devices includes the original
MK3721S and the new MK3721D. The MK3721D is a
drop-in replacement for the MK3721S device. Compared to
the earlier device, the MK3721D offers a wider operating
frequency range and improved power supply noise
rejection.
The MK3721 is a low cost, low-jitter, high-performance 3.3
volt VCXO designed to replace expensive discrete VCXOs
modules. The on-chip Voltage Controlled Crystal Oscillator
accepts a 0 to 3.3 V input voltage to cause the output
clocks to vary by ±100 ppm. Using ICS’ patented VCXO
techniques, the device uses an inexpensive external
pullable crystal in the range of 16.2 to 28 MHz to produce a
VCXO output clock at that same frequency.
ICS manufactures the largest variety of Set-Top Box and
multimedia clock synthesizers for all applications. If more
clock outputs are needed, see the MK3732 or MK377x
family of parts. Consult ICS to eliminate VCXOs, crystals,
and oscillators from your board.
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.
MK3721
Features
•
MK3721D is a drop-in replacement for the earlier
MK3721S device
•
•
•
•
•
•
•
•
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Packaged in 8-pin SOIC
Operational frequency range of 16.2 MHz to 28 MHz
Uses an inexpensive external crystal
On-chip patented VCXO with pull range of 200 ppm
(minimum)
VCXO tuning voltage of 0 to 3.3 V
Operating voltage of 3.3 V
12 mA output drive capability at TTL levels
Advanced, low-power, sub-micron CMOS process
For frequencies between 1 MHz and 8 MHz, use the
MK3713D. For higher than 28 MHz, use the MK3732-05.
•
Available in a lead-free package
MK3721D is recommended for new designs.
Block Diagram
VDD
VIN
X1
16.2 to 28 MHz
Pullable
Crystal X2
Voltage
Controlled
Crystal
Oscillator
16.2 to 28 MHz Clock
(REFOUT)
GND
IDT™ / ICS™
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
1
MK3721
REV E 103003
MK3721
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
VCXO
Pin Assignment
X1
VDD
VIN
GND
1
2
3
4
8
7
6
5
X2
DC
REFOUT
DC
MK3721S
MK3721D
8-Pi n ( 150 mi l ) SOI C
Pin Descriptions
Pin
Number
1
2
3
4
5
6
7
8
Pin
Name
XI
VDD
VIN
GND
DC
REFOUT
DC
X2
Pin
Type
Input
Power
Input
Power
--
Output
--
Input
Pin Description
Crystal connection. Connect to the external pullable crystal.
Connect to +3.3 V (0.01µf decoupling capacitor recommended).
Voltage input to VCXO. Zero to 3.3 V signal which controls the
VCXO frequency.
Connect to ground.
Do not connect to this pin.
VCXO CMOS level clock output matches the nominal frequency of
the crystal.
Do not connect anything to this pin.
Crystal connection. Connect to a pullable 16.2 to 28 MHz crystal.
IDT™ / ICS™
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
2
MK3721
REV E 103003
MK3721
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
VCXO
External Component Selection
The MK3721 requires a minimum number of external
components for proper operation.
as possible and should be on the same side of the PCB as
the MK3721. 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.
Decoupling Capacitors
A decoupling capacitor of 0.01µF should be connected
between VDD and GND on pins 2 and 4 as close to the
MK3721 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.
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.
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 MK3721 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
MK3721 incorporates on-chip variable load capacitors that
“pull” (change) the frequency of the crystal. The crystal
specified for use with the MK3721 is designed to have zero
frequency error when the total of on-chip + stray
capacitance is
14 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
The external crystal must be connected as close to the chip
IDT™ / ICS™
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
3
MK3721
REV E 103003
MK3721
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
VCXO
Absolute Maximum Ratings
Stresses above the ratings listed below can cause permanent damage to the MK3721. 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
+3.15
Typ.
–
Max.
+70
+3.45
Units
°C
V
Refer to page 3
IDT™ / ICS™
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
4
MK3721
REV E 103003
MK3721
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
VCXO
DC Electrical Characteristics
VDD=3.3V ±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.
3.15
2.4
Typ.
Max.
3.45
0.4
Units
V
V
V
V
VDD-0.4
6
±50
0
3.3
mA
mA
V
AC Electrical Characteristics
VDD = 3.3V ±5%,
Ambient Temperature 0 to +70° C, unless stated otherwise
Parameter
Output Frequency
MK3721D
MK3721S
Crystal Pullability
MK3721D
MK3721S
VCXO Gain
MK3721D
MK3721S
Output Rise Time
Output Fall Time
Output Clock Duty Cycle
Maximum Output Jitter,
short term
Symbol
F
O
F
O
F
P
F
P
24 MHz
Conditions
Min.
16.2
Typ.
Max. Units
28
MHz
MHz
ppm
ppm
24
+ 115
+ 100
120
140
1.5
1.5
40
50
110
60
0V< VIN < 3.3 V, Note 1
0V< VIN < 3.3 V, Note 1
VIN = VDD/2 + 1 V, Note 1
VIN = VDD/2 + 1 V, Note 1
ppm/V
ppm/V
ns
ns
%
ps
t
OR
t
OF
t
D
t
J
0.8 to 2.0 V, C
L
=15 pF
2.0 to 0.8 V, C
L
=15 pF
Measured at 1.4V, C
L
=15 pF
C
L
=15 pF
Note 1: External crystal device must conform with Pullable Crystal Specifications listed on page 3.
IDT™ / ICS™
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
5
MK3721
REV E 103003
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