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 IDT's 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. IDT 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 IDT 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 a PWM RC integrator circuit. Frequency output increases with VIN voltage input. The usable range of VIN is 0 to 3.3 V.


  • MK3721D is a drop-in replacement for the earlier MK3721S device
  • 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 lead (Pb) free package

tuneProduct Options

Part Number Part Status Pkg. Type Lead Count (#) Temp. Grade Pb (Lead) Free Carrier Type Buy Sample
Obsolete SOIC 8 C Yes Tube
Obsolete SOIC 8 C Yes Reel


Title language Type Format File Size Date
Datasheets & Errata
star MK3721 Datasheet Datasheet PDF 214 KB
Application Notes & White Papers
AN-841 Pullable Crystal Selection and VCXO Tuning Application Note PDF 334 KB
AN-848 VCXO - Crystal Selection Application Note PDF 222 KB
AN-849 Loop Filter Component Selection for VCXO Based PLLs Application Note PDF 218 KB
AN-847 VCXO - Absolute Pull Range Application Note PDF 155 KB
AN-800 Approved VCXO Crystals Application Note PDF 150 KB
Using IDT's Integrated VCXO Products MAN05 Application Note PDF 231 KB
Ferrite Bead Recommendations Application Note PDF 82 KB
PDN# : CQ-15-05 Market Declined Quarterly PDN Product Discontinuation Notice PDF 623 KB
PCN# : TB1504-01R1 Qty per Reel Standardization for Selective Packages Product Change Notice PDF 95 KB
PCN# : TB1504-01 Qty per Reel Standardization for Selective Packages Product Change Notice PDF 50 KB
PCN# : TB1303-02 Change of Tape & Reel Packing Method for Selective Products Product Change Notice PDF 361 KB
PCN# : A1208-01R1 Gold to Copper Wire Product Change Notice PDF 254 KB