ALPHA A little bit on type-C power distribution (PD)

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Thu Nov 29, 2018 4:23 am

After trying two USB type-c meter/diagnosis tools (one is a popular UM25C/UM34c) without much a success,
now that a new tool (WEB-U2) just arrived today, I'd like to share my finding...

1. first I have to upgrade WEB-U2's firmware to latest (now ver 4.7, very easy to do) to get a stable tester and probably more features

2.if I cascade other testers or odd ball cables, most cases the type-C protocol negotiation (over CC1 / CC2 leads < -- not D+ D-
leads) will fail. In such case, the power adapter only supplies 5V to Alpha and the Alpha will be as cold as rock. See #5, most likely stuck in BC1.2 DCP 5V 1.5A mode.

3. LPA supplied 45W power adapter with type-C plug, if direct connects to LPA, it will work, certainly. I also tried Apple 61W (seems to be a clone, since in one of WEB-U2's menu, it couldn't detect its S/N), this one has a type-C receptacle. I can use a type-C cable (plugs on both ends) to power LPA no problem.

4. With WEB-U2 added in the loop above, I saw the protocol used is PD 2.0 negotiated to 15V 3A in either Apple 61W or LPA 45W. Its screen show it's in "MTK PE" mode (should be equivalent to PD 2.0 mode.). Very important to note that both D+ and D- are left floating, most likely not connected to each other, and read as 0V. < -- this is critical (see later)

5. Important to note that LPA's 45W unit not only supports PD 2.0 (this is what this power supply arrangement should be), it also supports several others (such as QC2.0 up to 12V, QC3, BC 1.2 DCP 5V 1.5A.) The Apple 61W supports PD 2.0 as well as BC1.2 DCP 5V 1.5A.

6. Now the sequence is important... if I used #2 to trip LPA into "only getting 5V supply" feed, by using #4 method will not recover the LPA into (asking PD2.0 mode as default), i.e., even when using #4 method at this point, it is still getting 5V power feed, not PD 2.0's 15V feed.
Then if I use method #3, LPA is back to asking PD2.0 as the negotiation method and the system is now back to normal.

7. I am guessing somewhere in LPA side, type-C receptacle's D+ and D- still has some voltage and/or D+ D- is in a non-PD source or PD sink mode. This is the challenge a universal type-C (PD source, PD sink, accessory mode/OTG, and video mode) all-in-one design gave to us.

All my guesstimate and few things learned.
I am leaning toward a simpler power adapter (e.g., only support PD2.0 mode, no QC2, QC3, BC1.2 stuff) and probably taking out D+ and D- leads ( not sure, since USB PD is a complex standard) cto the power adapter end may help.

Anyway, I am back to 12V direct power DC plug solution. Easy, clean, and can also supply external devices are all big pluses.

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THW Mark
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Tue Jan 08, 2019 2:58 pm

this is a very interesting read - thanks for this. I'm looking into finding a PD USB C cable car charger for using the Alpha + 7" screen on the road, but there are very few options and i'm afraid they won't work. So maybe providing power to the pins would be better, except that I would probably have to add some circuitry to prevent voltage spikes/drops...

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Tue Jan 08, 2019 3:17 pm

Not USB type-C PD

For 12V automotive application and supplying power thru 4-pin DC PWR IN connector, use LTC3780 based solution
e.g., ... 2947310464
(set the correct output voltage first before hooking up)

I would also recommend adding a 2200uF 25V capacitor on its output end.

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Mon Jan 14, 2019 5:18 am

One thing I notice that happens in few USB type-C PD power adapter is that,
plug in the power adapter to AC first, then connect its USB cable to LP Alpha will work,
while keep the USB type-C cable always plug in to the LP Alpha, then connect the power adapter to AC sometimes would fail.

The main reason is that it takes time to get USB-C power adapter's internal capacitor's voltage level high enough such that USB-C protocol negotiation with LP Alpha can be successful <-- i.e., power adapter will be the supply sending out 15V to the connected device (LP Alpha)

Yes, it is tricky and is the ugly part of USB type-C spec.

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Sun Jan 20, 2019 3:12 am

@ T1g_i
re: Sometimes if I connect my Panda with the USB-C port, it does not start at all. I must connect it several times to power it up. What can that be?

The issue is related to USB-C PD negotiation. Such procedure happens very early, when "a slight bit of power that is sufficient enough" is supplied to LP Alpha.

What happens is that the USB-C power adapter has not reached the steady state ready to start the USB-C PD negotiation. <-- With LP Alpha, in normal state, it will negotiate to supplying 15V to LPA.
Once the negotiation failed, it will not reenter into the negotiation phase and the USB-C power adapter appears to be dead.

What do you do?
method 1: let the USB-C power adapter still connect to the AC socket. Pull it out, wait for 0.5 second, then immediately plug it back in.
< -- Idea is to let USB-C power adapter remain to have sufficient charge stored inside, unplug/replug to reset itself, then the PD-negotiation hopefully will start from a health ground (the charge inside the USB-PD adapter is high enough.)

method 2: unplug USB-C cable on LP Alpha side, plug in USB-C power adapter to AC socket first. then plug the USB-C cable to LP Alpha.
< -- using this method to do a quick test is fine. However, I do not recommend plug/unplug the USB-C cable on LPA side too many times. That requires delicatle operation to avoid damaging parts.

Other option is to use a different brand of USB-C PD power adapter.
These tend to not have integrated/unremovable cable on the power adapter side.
I will then always keep the power adapter plugged in and only connect/disconnec USB-C cable on the power adapter side.

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Tue Feb 05, 2019 2:24 am

Now I received the second Apple 61W USB-C PD power adapter, model A1718.
This time I make sure it is authentic/genuine/OEM and I had verified it is (using Web-U2 USB-C tester to check its S/N and there is one.)

However, there is a bad news. It is not usable for LP Alpha. The authentic one (made only for Apple) is not as versatile as the generic "Apple 61W adapter" you can find in fleaBay for cheap (usually less than $30 shipped.)
The authentic one only supports PD 2.0 in 3 settings: 5V, 9V, and 20V. < -- no 12V and most importantly no 15V support
LP Alpha will negotiate with it to get the power adapter to output 9V. As I had described before, LP Alpha's USB-C power in power sink mode, will not be awaken until the voltage is higher than 10.5V. Thus 9V will not be high enough to get LP Alpha to notice the power feed is available. I.e., as cold as dead.

In another word, buy generic but YMMV. Unfortunately, there are many clones and clone of clones. There is no way to tell if the so called "Apple USB-C 61W" will always supply 15V 3A in its internal offer capability table.
(Or try iClever one I mentioned here )

P.S. LP Alpha will not negotiate the power adapter to supply 20V (voltage is too high beyond spec. thus does not do so.)

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Tue May 07, 2019 9:56 am

It was relatively well documented previously that the apple USB "PD" charger *is not* PD spec compliant, it causes issues with many PD devices even when the supported voltages match.

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Tue May 07, 2019 9:58 am

The same also goes for Hewlett Packard and Huawei PD supplies, both of which apply proprietary extensions to ensure you're only using HP/Huawei products with them.

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Sat Dec 26, 2020 5:06 am

Adding info on using LattePanda Alpha/Delta's USB-C as power output (i.e., "PD Source" mode), when it is on 4-pin DC_IN or 10-pin Li-Pi battery pack as its power supply.

Disclaimer: I don't know the actual design spec and whether or not long term operation characteritics is consistent with what the power-negotiation protocol result is. So YMMV and I am definitely not responsible for any mishaps.

When LP Alpha/Delta's USB-C is supplying power, using a USB-C debugger/analyzer, I found it only support 5V 1.5A output, no other output voltage is supported.
When I use an adapter USB-C to USB 2.0 (type B socket), and use a QC trigger board,
it appears can/may support Apple Fast-charge 5V 2.4A mode.
<-- D+ lead thru 43K to V+, as well as, thru 50K to Gnd (which is 2.7V reference)
; also a separate circuit: D- lead thru 43K to V+, as well as, thru 50K to Gnd (which is 2.7V reference)
<-- Note: this is just protocol negotiation, actual power rating is TBD and I have no way to attest.

If I find a commercial dongle/trgger to do it properly, I'll post here. Currently, it's all DIY experimentation.

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Sun Dec 27, 2020 3:01 am

Re: using LP Alpha/Delta's USB-C port for supplying power

To be honest, using that USB-C port as PD Source mode is a good mental exercise.
However, in reality...
I'd like to ask you to think this way:
the LP Alpha is a $300++ SBC computer with many delicate parts.
The Supplied power adapter is just a 15V 3A power supply and the 4-pin DC_IN (Molex connector) is also not rated for high current flowing thru it.
I also do not think the LP Alpha/Delta itself with its tiny components is designed in a way to be a universal power supply to feed other high current drain devices in a long term, sustainable way.

15V 3A power supply is just a 45W power. LP Alpha/Delta with its devices (say, a high-end fast NVMe plus a large-screen eDP LCD display) on it own, altogether is reaching a comfortable margin of that 45W.
I don't really think it is a good engineering exercise to splice the power to feed another high-drain device (Rasp Pi computer.)

My thought in such case is to buy a good GaN power adapter (some are 65W, 100W, and even 120W), tiny, little heat, and multiple independent power-supplying ports. The pirce has dropped quite a bit in the $25-$45 range.
They are designed to do the work (supplying several loads at the same time) in the most optimized way.
And the best of all, it will not cause the LP Alpha/Delta itself to be a victim, a $300 loss, in a poweer-related mishap happens.

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