B Reference PRO
The Reference PRO board is used to program the LMX2571EPEVM and at the same time, provide a clean
reference clock to LMX2571EPEVM. The board has several control pins dedicated for control of output format,
output frequency, and output enable control. These control pins are configurable through the jumpers by
strapping the center pin to Vdd position or GND position. Connections from the Vdd position to the device
supply or from the GND position to the ground plane are connected by 1.5-kΩ resistors. By default, the board
is configured for 100-MHz LVPECL output. The power supply to Reference PRO is obtained from the PC that is
connecting to Reference PRO through the USB interface.
B.1 Output Frequency Selection
Jumpers FS1 and FS0 are used to set the output frequency.
Table B-1. Reference PRO Output Frequency Selection
FS1
FS0
OUTPUT FREQUENCY (MHz)
GND
GND
100
GND
NC
312.5
GND
Vdd
125
NC
GND
106.25
NC
NC
156.25
NC
Vdd
212.5
Vdd
GND
62.5
B.2 Output Format Selection
The OE pin is used to enable or disable the output.
The OS pin is used to bias internal drivers and change the output format.
Table B-2. Reference PRO Output Format Selection
OE
OS
OUTPUT FORMAT
GND
Don't Care
Disabled
Vdd
GND
LVPECL
Vdd
NC
LVDS
Vdd
Vdd
HCSL
It is imperative to match the output termination passive components as shown in
Table B-3. Output Termination Configuration
OUTPUT FORMAT
COUPLING
COMPONENT
VALUE
LVPECL
AC (Default configuration)
R15, R28
0 Ω
R26, R29
150 Ω
C24, C25
0.01 µF
R27, R30, R31
DNP
DC
R15, R28, C24, C25
0 Ω
R26, R27, R29, R30, R31
DNP
LVDS
AC
R25, R27, R28, R30
0 Ω
R31
100 Ω
C24, C25
0.01 µF
R26, R29
DNP
DC
R25, R27, R28, R30, C24, C25
0 Ω
R31
100 Ω
R26, R29
DNP
Reference PRO
16
LMX2571EPEVM Evaluation Instructions
SNAU182 – MARCH 2021
Copyright © 2021 Texas Instruments Incorporated
