I only have old USB 2.0 Charger Doctor, so I could only test power requirements at USB 2 data throughput rates.
My cabling was configured like this:
USB 3.0 port on computer->USB 2.0 extension cable->USB 2.0 Charger Doctor->USB 3.0 cable->LimeSDR-USB
Here is the firmware, hardware and gateware versions, because I’m guessing that the power required will vary between versions (hopefully future versions using less power when inactive):
[22:17:21] INFO: Connected Control port: LimeSDR-USB FW:4 HW:4 Protocol:1 GW:2.16 Ref Clk: 30.72 MHz
I ran some of the tests a few times because USB 2.0 can be problematic, and I’d only trust the accuracy of the Charger Doctor to one decimal place if I’m totally honest.
900 mA at 5 Volts (4.5 Watts) is the maximum that a USB 3.0 port should be able to supply, I think you are best to assume that is how much power you will need when the device is fully active and actually processing data. Not just plugged in and idle.
no device connected (checking USB port looks nominal with no load)
[0.00 Amps 5.02 Volts ~= 0 watts]
[0.00 Amps 5.02 Volts ~= 0 watts]
LimeSDR USB plugged in no software running (2 solid green LED’s and 1 flashing red/green LED) - an idle board.
[0.81 Amps 4.59 Volts ~= 3.72 Watts]
[0.80 Amps 4.58 Volts ~= 3.66 Watts]
Running “LimeSuiteGUI_20180406_d6bc28”
Options->ConnectionSettings
Highlighted device and clicked on connect (2 solid green LED’s and 1 flashing red/green LED)
Just connected but not doing anything else
[0.81 Amps 4.59 Volts ~= 3.72 Watts]
[0.81 Amps 4.57 Volts ~= 3.70 Watts]
While connected and clicked on “Default” (2 solid green LED’s and 1 flashing green LED)
[0.79 Amps 4.52 Volts ~= 3.57 Watts]
[0.86 Amps 4.55 Volts ~= 3.91 Watts]
I partially ran through the “Loopback test” (1 solid green LED, 1 solid red LED, 1 flashing green LED)
I set the CLKGEN, Frequency control CLK_H (MHz) to 16, which should work with USB 2.0 (~6.023MB/s)
[1.18 Amps 4.43 Volts ~= 5.23 watts]
I set the CLKGEN, Frequency control CLK_H (MHz) to 24, which should work with USB 2.0 (~9.035MB/s)
[1.19 Amps 4.42 Volts ~= 5.26 watts]
I set the CLKGEN, Frequency control CLK_H (MHz) to 32, which should work with USB 2.0 (~12.047MB/s)
[1.19 Amps 4.42 Volts ~= 5.26 watts]
I set the CLKGEN, Frequency control CLK_H (MHz) to 36, which should work with USB 2.0 (~27.099MB/s)
[1.19 Amps 4.42 Volts ~= 5.26 watts]
I set the CLKGEN, Frequency control CLK_H (MHz) to 40, which may work with USB 2.0 (~30.116MB/s)
[1.20 Amps 4.44 Volts ~= 5.33 watts]
Looking at the above numbers, I’m starting to think that my Charger Doctor needs an upgrade to a more accurate device. One that fully supports USB 3 and/or USB-C. It claims to function from 3.5 to 7 Volts and 0 to 3 Amps, if you assume that it is accurate to +/-20% then the above numbers start to look more reasonable. I bought for 0.99 cents from aliexpress so it is not going to be the most accurate device. But it does give a rough feel for the power levels.