USB-CYBERCLOCK - For low-noise VCOs&PLLs （2）

Published:2011/8/10 1:13:00 Author:Phyllis From:SeekIC

By Burkhard Kainka

The CY27EE16 (’One-PLL In-System Programmable Clock Generator with Individual 16K EEPROM’) is particularly interesting for low volume production applications or circuit development. The internal EEPROM does not need a special programmer; it can be programmed via the built-in l2C bus interface. Register contents can also be overwritten ’on the fly’ as above. A default configuration can be programmed into the chip and this will be loaded each time at power up. This facility brings the concept of an individually programmable oscillator one step closer. The internal structure of the chip (Figure 3) shows the possibilities for clock generation using just one PLL. The output dividers can be internally connected to either the VCO output or directly from the reference clock. One frequency can be freely chosen while the other outputs must be derived from the VCO or reference frequency.





Both ICs allow direct connection of a crystal in the range between 8 MHz and 30 MHz. The output frequency is selectable up to 200 MHz.

A range of evaluation boards from Cypress featuring USB connectivity supports the family of clock generator chips. These boards are known as ’Candy Boards’ (presumably because they are simple to use). The ’Peppermint board’ has the CY22393 fitted while the ’Blueberry board’ contains the CY27EE16. Each of these evaluation boards is a versatile stand-alone universal frequency generator and can be used in many applications. Cyber-Clocks (Figure 4) is a free program that greatly simplifies the process of directly programming and controlling the Candy Boards.





Cypress also produces free downloadable software supporting the entire range of clock generators. From the CyberClock start menu select the sub-family then the chip part number. The CY22393 can be found under CyClocksRT while the CY27EE16 is under ISR.

The program displays a window for the selected chip with the programming options. The desired output frequency and the input clock frequency can be entered along with the pinout configuration and the software will calculate the division factors Q, P and N and also all the necessary internal register values. The settings can be saved in a JEDEC format file that is compatible with most hardware programmers. The starter boards also feature a USB interface.

The Peppermint Board

The demo board type CY30701 (Peppermint Board) is fitted with the CY22393 and contains an on-board 10 MHz crystal together with a USB interface. The CyberClccks program can be used to configure the chip once the desired output frequencies are entered.

The example in Figure 5 shows the generation of three different frequencies in the range between 6.55 MHz and 122 MHz. A buffered output clock from the quartz oscillator is also used as an output. With the software in Advanced Mode it is possible to see all the configuration settings. Details of each of the PLL and divider settings as well as all the internal links are shown. Another program feature that proved useful during system development is the Bit-Viewer, this displays the contents of all the internal registers.





When the Peppermint board is first connected to the PC it should be automatically detected and the appropriate Human Interface Device (HID) driver will be loaded by Windows. An on-board status LED will blink to indicate successful USB communication.

The board takes its power directly from the +5 V USB and has an on-board 3.3 V voltage regulator. Programmed settings will be retained on the board as long as it is powered up. Once power is disconnected the settings will revert to their default example values.

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