Low Phase Noise Clock Evaluation Board User's Guide

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ChronosGUI
Table 1 lists the various menu items in this screen.
Table 1. Software Settings Description
Section Function
VCO Select Selects between VCO1 and VCO2. Only one VCO can be used
during operation. See CDCE421 data sheet for VCO tuning ranges.
Prescalar The prescalar selection is determined in conjunction with VCO and
output divider selection. See the CDCE421 data sheet to determine
the proper setting.
Output Divider The output divider is determined in conjunction with the VCO and
prescalar settings. See the CDCE421 data sheet to determine the
proper setting.
Driver Select Selects between LVPECL or LVDS output.
PECL Config This option should be activated when using LVPECL output. When
selected, the USB controller enables the onboard LVPECL
termination.
Charge Pump Current Selects appropriate charge pump current. See Figure 6 and Figure 7
for recommended configurations.
Loop Filter Bias Select Bias 0 should be used at all times. Bias 1 is a test mode reserved for
factory use.
Loop Filter Selects the loop filter C and R values. See Figure 6 and Figure 7 for
recommended configurations.
VCO Calibration When Enable VCO Calibration is selected, the CDCE421 uses its
internal calibration circuit to lock the PLL loop. VCO Calibration
Override should not be checked. TI uses manual calibration for test
modes.
TI Test Use Setting should be kept at 0000 ibias_100ua. Other settings are for
TI use only.
Chronos IC Config Select Use U13 programming socket for rapid programming of
Chronos-enabled devices.
Select Use U8 DIE/U9 QFN socket if the EVM is using a
direct-mounted die or a QFN-mounted device (typical configuration).
Select Use U12XTAL EVAL if using the optional 6-pin XO mounting
pads (for Chronos-enabled oscillators).
Chronos Control Select Enable Power to run the entire board from the host USB
voltage. In this mode, the EVM does not need an external 3.3V
power supply. If this option is not selected, then an external 3.3V
supply and ground connection must be attached.
Select Output Enable to provide a clock output. When not selected,
the output goes to a high-Z state.
Push Write Chronos settings to RAM to download settings into the
CDCE421 on-chip volatile SRAM. These settings are lost upon
device power-down.
Push Write Chronos settings to EEPROM NO LOCKING when ready
to store the configuration in the CDCE421 nonvolatile EEPROM. The
settings are available after device power-down. The settings can be
changed at a later time.
Push Write Chronos settings to EEPROM LOCKING only if the
settings are permanent and final. After this selection, the
EEPROM is locked and cannot be altered at a later time.
USB Communication A bright red light indicates that USB is not connected or not
communicating properly. A green light indicates that a proper USB
connection exists.
10.9MHz–1175MHz Low Phase Noise Clock Evaluation Board12 SCAU020 – March 2007
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