Datasheet

7 Configuring the Board
7.1 Configuration for Programming and Testing (with USB Cable Attached)—Default
Configuring the Board www.ti.com
Table 1. Advanced Control: Software Setting Options (continued)
Section Function
Selects the loop filter C and R values. See screen shotsxx for
Loop Filter
recommended configurations.
When Enable VCO Calibration is selected, the CDCE421A
will use its internal calibration circuit to lock the PLL loop.
VCO Calibration
VCO Calibration Override should not be checked. (TI uses
manual calibration for test modes.)
This setting should be kept at 0000 ibias_100ua. Other
TI Test Use
settings are for TI internal 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. Note:
This setting is the 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 will not need
an external 3.3-V power supply. If this option is not
selected, then a 3.3-V supply and ground connection
must be attached.
• Select Output Enable to provide a clock output. When
not selected, the output will go to a high-Z state.
• Push Write Chronos settings to RAM to download
settings to the CDCE421A onboard volatile SRAM.
These settings will be lost upon power down.
• Push Write Chronos settings to EEPROM NO LOCKING
when ready to store the configuration in the CDCE421A
nonvolatile EEPROM. The settings will be available after
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 will be locked and cannot be
altered at a later time.
A bright red light indicates that USB is not connected or not
USB communication communicating properly. A green light indicates a proper
USB connection.
The CDCE421AEVM can be powered from either the USB power supply or from an external source. The
CDCE421AEVM only requires a USB cable to be attached for programming purposes; however, for test
measurements, it is recommended to also use an external 3.3-V power supply. Test measurements can
also be taken with only the USB-supplied power. However, as a result of USB power variances, results
may degrade. It is also possible to program the CDCE421A and then disconnect the USB cable with minor
board configuration changes. To enable power and programming of any of the four blocks on the
CDCE421AEVM, the respective switch must be turned on, as explained earlier (see Section 2 ).
Configuration
The CDCE421AEVM is configured by default to operate with the USB cable attached and a 3.3-V power
supply added to AUX VDD and GND. In this configuration, the USB microcontroller is powered by the USB
port 5-V supply while the CDCE421A is powered by the 3.3-V external supply. This setup is optimal for
programming the CDCE421A while also taking measurements. This configuration removes the power
variation found in USB power supplies by isolating the CDCE421A from the USB supply.
10.9-MHz to 1.175-GHz, Low Phase Noise Clock Evaluation Board10 SCAU031 – June 2009
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