Waveforms throws error when connecting to AD2 via USB Isolator

[s4fq7]

Hello I recently wanted to use a USB isolator with my AD2 in waveforms.

I purchased the same FullSpeed capable (not High-Speed) USB isolator as discussed in this blog post.

https://www.electrobob.com/analog-discovery-usb-isolation/

I made the same modifications he details, an increased power up to 3W, 1A fuse and a 470 uF capacitor.

I connected the AD2 via the USB isolator to computer and it was detected fine however when I try and launch waveforms it throws the following error.

 

```

Device opening failed

DptiIO failed ERC:7 out:16 in:0

Device configuration failed (PLL 2).

USB: 4.81V 73mA AUX: 0.00V 0mA

```

 

I'm a little uncertain what the source of the issue is with my USB isolator.

I'm hoping someone who has access to the WaveForms source can tell me what the error means.

It seems like maybe there is some issue with the available current as it includes 73mA in the error message, but I'm not sure.

I did buy 4 of them and solder them all identically and they all appear to throw the same error.

I wonder if perhaps something has changed that means it isn't possible to modify these FullSpeed USB isolators for use with the AD2...

 

I have one different USB isolator by a different manufacturer which doesn't have the power modifications made so it isn't capable of supplying enough current to the AD2. When I try to connect with WaveForms to an AD2 via this different USB isolator I get a different error which clearly says there isn't enough power.

```

Device opening failed

Device configuration failed (Post AVCC).

The device needs at least 2W/400mA from USB cable. To satisfy this:

- Try to use different USB cable and computer plug.

- Use the USB plug on the back of the PC, not the one on the front panel.

- Use short cable, do not use long cable or cable extender.

- Use powered USB-hub, avoid un-powered hub.

- Use 6V auxiliary power supply.

USB: 4.97 73ma AUX: 0.00V 0mA

```

So since when I am using the modified usb isolator cable of putting out 3W I don't get this power error it seems like it is receiving enough additional power. Also it looks like the original error I was getting isn't related to a power issue perhaps as the power details appear to be included with every error.

Can anyone tell me what is failing when it shows me the following error?

```

DptiIO failed ERC:7 out:16 in:0

Device configuration failed (PLL 2).

```

Update 2:

I just tried connecting a 5V power supply to the unit and it seems that with the 5V power supply connected it allows me to connect.

I wonder if perhaps there is some issue with the 5V DC DC isolation transformers taking too long to respond, or perhaps the 470uF capacitor is insufficient.... It doesn't say there is insufficient power, but the error might indicate the power is not stable perhaps ...

Update 3:

I attached a usb power supply to 3 of the same 5V DC-DC isolators and fed that into the AUX power input on an analog discovery.

The power supplied via the exact same buck converts via the AUX input caused the device to function fine.

It seems there is something about supplying the this same power via the USB cable to the AD2 that is resulting in the issue....

I'm going to try running two wires directly from the USB power lines into the AUX power input to see if that works as well...

Thanks!

Edited September 25, 2022 by s4fq7
extra details

[s4fq7]

So I found the issue.

There is a 6.8uH 0603 inductor located between the two capacitors on VBUS right after the fuse.

This perfectly matches the inductor suggested in the "EMC (Class B) compliance circuit" shown on page 4 of the 5V DCDC isolation transformer datasheet.

https://www.digikey.com/en/products/detail/mornsun-america-llc/B0505S-1WR3/13168098

Unfortunately according to the datasheet this inductor has a maximum rated current of 330mA based on temperature rise.

https://www.digikey.com/en/products/detail/murata-electronics/LQM18DN6R8M70L/12476589

This current limit corresponded to the maximum current I was seeing when using the USB isolator PCB.

For the time being I shorted this inductor out and it is now driving enough current through the 3 5V DCDC isolation transformers to power the AD2.

I'm unsure why the person who wrote the original blog article I was following didn't hit into this issue.

Perhaps the AD (original) used slightly less current than the AD2.