MDS 3721 E 1Revision 103003
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
MK3721
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 ea rlier device, the MK3721D of fers 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 exte rnal pullab le 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 cloc k 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-imp edance inpu t, it can be driv en directly
from an PWM RC integrator circuit. Frequency output
increases wit h VIN v oltage input. The usable range of
VIN is 0 to 3.3 V.
Features
•MK3721D is a drop-in replacement for the earlier
MK3721S device
•Packaged in 8-pin SOIC
•Operat ional freque ncy ran ge 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
•F or f requencies bet we en 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
X1
X2
Voltage
Controlled
Crystal
Oscillator
VIN
16.2 to 28 MHz
Pullable
Crystal
16.2 to 28 MHz Clock
(REFOUT)
GND
VDD
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
MDS 3721 E 2Revision 103003
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK3721
Pin Assignment
Pin Descriptions
X1
VDD
VIN
DC
GND
REFOUT
DC
X21
2
3
4
8
7
6
5
MK3721S
MK3721D
8-Pin (150 mil) SOIC
Pin
Number Pin
Name Pin
Type Pin Description
1 XI Input Crystal connection. Connect to the external pullable crystal.
2 VDD Power Connect to +3.3 V (0.01µf decoupling capacitor recommended).
3 VIN Input Voltage input to VCXO. Zero to 3.3 V signal which controls the
VCXO frequency.
4 GND Power Connect to ground.
5 DC -- Do not connect to this pin.
6 REFOUT Output VCXO CMOS le v el cloc k output ma tches the nomina l frequency of
the crystal.
7 DC -- Do not connect anything to this pin.
8 X2 Input Crystal connection. Connect to a pullable 16.2 to 28 MHz crystal.
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
MDS 3721 E 3Revision 103003
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK3721
External Component Selectio n
The MK3721 requires a minimum number of external
components for proper operation.
Decoupling Capacitors
A decoupling capacitor of 0. 01µF should be conne cted
between VDD a nd GND on pins 2 and 4 as close to the
MK3721 as possible. F or optimum de vice performance,
the decouplin g cap a cito r sh ou ld be mo un te d on the
component side of the PCB . Avoid the use of vias in the
decoupling circuit.
Series Termination Resistor
When the PCB tra ce be tween the clock outpu t a nd the
load is over 1 inch, series termination should be used.
To series ter minate 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
possib le. The nominal impe dance of the cloc k output is
20Ω.
Quartz Crystal
The MK3721 VCXO function consist s 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 MK37 21 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±20 ppm
Temperature Stability ±30 ppm
Aging ±20 ppm
Load Capacitance 14 pf
Shunt Capacitance, C0 7 pF Max
C0/C1 Ratio 250 Max
Equivalent Series Resistance 35 Ω Max
The e xternal crystal must be connected as close to the
chip as possib le and should be on th e same side of the
PCB as the MK3721. There should be no via’ s betw een
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 la yout. 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.
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
MDS 3721 E 4Revision 103003
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK3721
Absolute Maximum Ratings
Stresses above the rat ings listed below can cause permanent damage to the MK3721. These ratings,
which are standard v alues f or ICS commercially rated pa rts , are stress ratings on ly. Functional opera tion 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.
Recommended Operation Conditions
Item Rating
Supply Voltage, VDD 7 V
All Inputs and Outputs -0.5 V to VDD+0.5 V
Ambient Operating Temperature 0 to +70°C
Storage Temperature -65 to +150°C
Soldering Temperature 260°C
Parameter Min. Typ. Max. Units
Ambient Operating Temperature 0 – +70 °C
Power Supply Voltage (measured in respect to GND) +3.15 +3.45 V
Reference crystal parameters Refer to pag e 3
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
MDS 3721 E 5Revision 103003
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK3721
DC Electrical Characteristics
VDD=3.3V ±5% , Ambient temperature 0 to +70°C, un less stated otherwise
AC Electrical Characteristics
VDD = 3.3V ±5%, Ambient Temperature 0 to +70° C, unless stated otherwise
Note 1: External crystal device must conform with Pullable Crystal Specifications listed on page 3.
Parameter Symbol Conditions Min. Typ. Max. Units
Operating Voltage VDD 3.15 3.45 V
Output High Voltage VOH IOH = -12 mA 2.4 V
Output Low Voltage VOL IOL = 12 mA 0.4 V
Output High Voltage (CMOS
Level) VOH IOH = -4 mA VDD-0.4 V
Operating Supply Current IDD No load 6 mA
Short Circuit Current IOS ±50 mA
VIN, VCXO Control Voltage VIA 03.3V
Parameter Symbol Conditions Min. Typ. Max. Units
Output Frequency
MK3721D FO16.2 28 MHz
MK3721S FO24 MHz 24 MHz
Crystal Pullability
MK3721D FP0V< VIN < 3.3 V, Note 1 + 115 ppm
MK3721S FP0V< VIN < 3.3 V, Note 1 + 100 ppm
VCXO Gain
MK3721D VIN = VDD/2 + 1 V, Note 1 120 ppm/V
MK3721S VIN = VDD/2 + 1 V, Note 1 140 ppm/V
Output Rise Time tOR 0.8 to 2.0 V, CL=15 pF 1.5 n s
Output Fall Time tOF 2.0 to 0.8 V, CL=15 pF 1.5 ns
Output Clock Duty Cycle tDMeasured at 1.4V, CL=15 pF 40 50 60 %
Maximum Output Jitter,
short te rm tJCL=15 pF 110 ps
LOW COST 16.2 TO 28 MHZ 3.3 VOLT VCXO
MDS 3721 E 6Revision 103003
Integrated Circuit Systems ● 525 Race Street, San Jose, CA 95126 ● tel (408) 297-1201 ● www.icst.com
MK3721
D
EH
c
h x 450
be
Q
A
Pin 1
Index
Area
Package Outline and Package Dimensions (8-pin SOIC)
Package dime nsions are kept current with JEDEC Publication No. 95
Ordering Information
Note 1: MK3721D is recommended for new designs.
While the information presented herein has been check ed for both accuracy and reliability, Integrated Circuit Systems (ICS)
assumes no responsibility for either its use or for the infringement of any patents or other rights of third parties, which would
result from its use. No other circuits, patents, or licenses are implied. This product is intended for use in normal commercial
applications. Any other applications such as those requiring extended temperature range, high reliability, or other extraordinary
environmental requirements are not recommended withou t additional processing by ICS. ICS reserves the right to change any
circuitr y or specifications without notice. ICS does not authorize or warrant any ICS product fo r use in life support devices or
critical medical instruments.
Part / Order Number
(Note 1) Marking Shipping
packaging Package Temperature
MK3721D MK3721D Tubes 8-pin SOIC 0 to +70° C
MK3721DTR MK3721D Tape and Reel 8-pin SOIC 0 to +70° C
MK3721DLF MK3721DL Tubes 8-pin SOIC 0 to +70° C
MK3721DLFTR MK3721DL Tape and Reel 8-pin SOIC 0 to +70° C
MK3721S MK3721S Tubes 8-pin SOIC 0 to +70° C
MK3721STR MK3721S Tape and Reel 8-pin SOIC 0 to +70° C
Millimeters Inches
Symbol Min Max Min Max
A 1.35 1.75 0.0532 0.0688
A1 1.10 0.25 0.0040 0.0098
B 0.33 0.51 0.013 0.020
C 0.19 0.25 0.0075 0.0098
D 4.80 5.00 .1890 .1968
E 3.80 4.00 0.1497 0.1574
e 1.27 Basic 0.050 Basic
H 5.80 6.20 0.2284 0.2440
h 0.25 0.50 0.010 0.020
L 0.40 1.27 0.016 0.050
a0°8°0°8°
