Voltage Controlled Crystal Oscillators are very similar to Crystal Oscillators but they have a VC pin which allows the customer to change or pull the output frequency by a certain number of ppm by changing the voltage supplied to the VC pin. The onsemi VCXOs provide a + or – 100 ppm pulling range. That is, the output frequency can have up to 100 ppm less or up to 100 ppm more than the output frequency specified in the datasheet. To obtain -100 ppm, the voltage on VC must be equal to 0 V. To obtain +100 ppm, the voltage on VC must be equal to Vdd. To get the output frequency specified in the datasheet the voltage on VC must be Vdd divided by 2.