I have the CW305 set up with an external power supply. The supply is outputting 1V according to the display and my (Fluke) multimeter. When I connect it to the CW305 board and programmed the FPGA the displayed voltage is .85-.900. I double checked with a second set of banana jacks from the board VCC-INT to my multimeter and got a similar reading of .85-.900 Volts.
My question, is this the correct way to verify the voltage? Should I increase the DC supply until my meter reads 1.0V? I am afraid of damaging the board since the unloaded measurement was 1V.
It seems the device is slightly undervolted when I run my AES test, because when I use the USB power supply it works however when I switch to VCC-INT my design produces incorrect outputs (either all zeros or random bytes).
This is strange. I would definitely NOT increase your supply until 1.0V is measured. As you can see the CW305 FPGA does not tolerate very much over-volting; you would risk destroying it. I feel the most likely explanation is that your DC supply is defective and is failing under load. Are you able to test it with another load drawing a similar current?
I can try it with a resistor and breadboard I suppose.
I am surprised if it’s the supply as it’s very new. The seven segment displays on the FPGA also read a .85-.900 voltage. Could it be that the wires I am using are that bad? They are run of the mill banana jack cables.
My DC supply also has remote sense, do you think it would be advisble to try that and tie the sense probes to the vcc-int test points?
@jpthibault
I’ve just tested the following and can replicated it with a new power supply and new CW305:
I turned off the board and plugged in the leads from the DC Power supply to the VCC-INT, and then measured TPVIN and GND with my multimeter. When the board is unpowered, I read the expected 1 volt.
Next, I powered on the board and switched the VCC-INT switch to the position which selects the Internal 1V regulator. The multimeter still shows the expected 1V reading in this configuration.
When I switch the position to select the external power supply, I observe a 150-200mV drop on my multimeter. This is observed even when the board is off (all LEDs off). This reading is consistent with both the multimeter and the seven segment display. However, the DC supply shows 1V.
Again, I replicated similar behavior with a different DC supply and different CW305.
So it seems that there is some voltage drop when using an external supply, when the switch is activated. Any idea what is happening and how to proceed?
So, I realized that the only untested part in the measurement chain are the cables from DC to the board. I switched them out and noticed a different, but much lower voltage drop. So I would conclude it’s the cables. I guess at 1V, cable choice can make a difference if they’re long and thin. We’ve ordered thicker and shorter ones.