S i 5 3 4 5 - E V B
8
Rev. 1.1
10.2. Additional Power Supplies
Although additional power (besides the power supplied by the host PC’s USB port) is not needed for most
configurations, two addi5 VDC power supplies (MAIN and AUX) can be connected to J33 and J34 (located
on the bottom of the board, near the USB connector). Refer to the Si5345-EVB schematic for details.
The Si5345-EB comes pre-configured with jumpers installed at JP15 and JP16 (pins 1-2 in both cases) in order to
select “USB”. These jumpers, together with the components installed, configure the evaluation board to obtain all
+5 V power solely through the main USB connector at J37. This setup is the default configuration and should
normally be sufficient.
Figure 8 shows the correct installation of the jumper shunts at JP15 and JP16 for default or standard operation.
Figure 8. JP15-JP16 Standard Jumper Shunt Installation
Errata Note:
Some early versions of the 64-pin Si534x-EVBs may have the silkscreen text at JP15-JP16 reversed regarding
EXT and USB, i.e., USB EXT instead of EXT USB. Regardless, the correct installation of the jumper shunts for
default or standard operation is on the right hand side as read and viewed in Figure 8.
The general guidelines for single USB power supply operation are listed below:
Use either a USB 3.0 or USB 2.0 port. These ports are specified to supply 900 mA and 500 mA
respectively at +5 V.
If you are working with a USB 2.0 port and you are current limited, turn off enough DUT output voltage
regulators to drop the total DUT current
≤
470 mA. (Note: USB 2.0 ports may supply > 500 mA. Provided
the n5 V drops gracefully by less than 10%, the EVB will still work.)
If you are working with a USB 2.0 and you are current limited and need all output clock drivers enabled,
re-configure the EVB to drive the DUT output voltage regulators from an ex5 V power supply as
follows:
Connect ex5 V power supply to terminal block J33 on the back side of the PCB.
Move the jumper at JP15 from pins 1-2 USB to pins 2-3 EXT.
