P2-ES psu woes
cheezus
Posts: 295
I've finally come to the point where I need to use an external brick to power my project. This isn't a surprise given the large 5v current (500ma) as well as the 3v3 @150ma. I've got all pin jumpers set to VIO so to use the switching reg. I'm using pins 0-24 so these groups will probably need to stay @ VIO. I haven't moved these jumpers yet since I haven't found a need, haven't had a chance to mess with VGA or anything..
I've been testing things with ~40ma on the 5v rail, not sure the 3v3 draw. But after connecting the larger 5v draw, the P2 no longer responds. I haven't done much troubleshooting yet since I've been surprised things worked so far on the desktop's USB current alone. Like I said I have a 5v brick (phone charger) I plan on using as "supplemental" supply but I'm wondering if there's an edge-case that needs to be prevented?
I'm thinking the power up sequence should be
PC-usb -> P2-usb
and power down is
P2-usb -> PC-usb
but I'm not really sure? Sorry if this has been answered before. Thanks in advance!
I've been testing things with ~40ma on the 5v rail, not sure the 3v3 draw. But after connecting the larger 5v draw, the P2 no longer responds. I haven't done much troubleshooting yet since I've been surprised things worked so far on the desktop's USB current alone. Like I said I have a 5v brick (phone charger) I plan on using as "supplemental" supply but I'm wondering if there's an edge-case that needs to be prevented?
I'm thinking the power up sequence should be
PC-usb -> P2-usb
and power down is
P2-usb -> PC-usb
but I'm not really sure? Sorry if this has been answered before. Thanks in advance!
Comments
Here's sharing some background info...
It shouldn't matter, but there 'might' be an edge case that occurs when the P2-ES has a heavy load attached during the time that the USB port is negotiating. (when plugging in the PC-USB cable and waiting for the PC to signal that 500mA can be consumed). If the negotiation takes too long, there is a body diode in one of the USB switches that might be passing too much current for too long.
It's speculation, and we've designed it out just to be safe on the next Eval board. But it wouldn't hurt to follow your sequence just in case.
Another possible reason for failure of those switches (as was experienced by a couple of forumistas) would be an unexpected short between 5V and VIO on one of the accessory headers. Those pins have also been protected for the next Eval board. Ensuring those two pins don't get shorted on the revA Eval is certainly something to take care of.
Thanks for confirming that. In hindsight I should have designed some solder jumpers that would allow me to isolate different sections. As it is, I have one big power net with multiple possible sources. Great learning experience for the next few board layouts though
I've gone with a mains powered USB hub which has handy per port on-off switches. Eliminates all the replugging.
Evanh is right.
That is what I thought I read in your first post, but somehow must have been standing on my head this morning.
Connect the aux power first (P2-USB). Then hook up the PC-USB connection.
Disconnect in reverse.
I'm still trying to figure out my "tangle" of power. I really wish I had a way to isolate the 5v (and 3v3) from the P2es to my pcb but that would require using lots of jumper wires. Hindsight is 20/20 though and I still don't have a GOOD reason to do another board run.
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glad I didn't hit post before I tried plugging things in
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I'm not sure when, or how but I think I damaged the AUX usb switch U501. Not real sure what happened although I'm pretty sure it's not the high current draw or 5v / vio short. Symptom is when powered from AUX, usb AUX active led lit but no power to 5v common. I'll have to get my meter out later and double check.. So I guess this post is kinda pointless now! My bad...
I have to figure out what the BEST solution is for now, and for permanent. I'm considering powering from 5v common on 2x6 header, from tbd psu.. But to do this I'd need to either not use the PC usb port, reprogram ftdi to ?float? cbus3 or pull U502? I have a couple prop plugs floating around so that seems like an easy solution to programming without using the onboard ftdi. Main issue now I think is finding the right 5v supply.
I've desoldered U501 on my board and bridged across pads from AUX to 5 Volt Common. Has worked well. Be sure to double check soldering is correct as it's a small working area with plenty of nearby surface-mount contacts.
The down side is it permanently disables the other USB switch.
An alternative approach is bridge across F401 near PC-USB connector. This will boost the strength of PC-USB supply a lot if the cable is rated for it. Certainly a lot easier to do than removing U501.
PS: F401 is called a PTC resettable fuse but it's really a thermistor like device. The operating resistance is terrible, so bridging it out makes the supply from PC-USB much stronger.
" Discharge Function The discharge function of the device is active when enable is disabled or de-asserted. The discharge function with the N-MOS power switch implementation is activated and offers a resistive discharge path for the external storage capacitor. This is designed for discharging any residue of the output voltage when either no external output resistance or load resistance is present at the output. "
https://www.diodes.com/assets/Datasheets/AP22802.pdf
To me this presents a direct path from 5v_common to vss through the switch. I'm guessing the discharge function is only activated on a falling edge condition. Seems the edge case here would be "falling edge on 5v_usb_aux, while powered from 5v usb" ?
*added block diagram
It's what I would expect but doesn't seem to be the case. Still need to do some probing to confirm. PC usb switch seems to be okay, and P2 usb switch seems to have failed open.
Right now I'm thinking about bypassing 5v_aux to 5v_common as you have, except I'm going to try a jumper from the unsoldered 2 pin connector to a 5v on 2x6 headers. Looking at the store, the powerpal looks nice right now. Give me an excuse to finally order that WX
Note: When soldering the Vss pin of that 2-pin AUX header it takes a lot of heat before it'll wick right through.
I really wish there were test points for some of the nets. Getting to 5v_USB and USB_PWREN# doesn't look very easy. I guess the bypass is going to be best for now, time to change the tip in my iron. Can't do much of anything until I find a 5v supply that I actually trust and although I don't THINK it had anything to do with the dumb phone brick... Kinda stuck deciding how overkill my 5v supply really needs to be.
#whyengineersdrink
*edit
I'm trying to think this through fully. You COULD power through an accessory header, but if you don't have the bypass (either method should work) then won't there be contention when powered from 5v_usb? The jumper avoids the "permanent" disabling of 5v_usb, but still turns U502 off.
I'm trying to figure out how to SAFELY test this. Willing to sacrifice U502 "for the good of the cause" if I can figure out exactly HOW to isolate and replicate this error. I THINK..
1- plug usb-pc, allow enumerate
2- apply power to AUX, turns off U502
3- U502 turning off enters discharge mode, low resistance path 5v_common to ground
4-???
5- U502 should be blown!
I'm considering removing U501 since it's known faulty to see if latch up condition continues. Either U501 is "leaking" OUT -> IN or U503 is "leaking" somewhere.
Just thought I'd update since I have some actual answers. Now to find a nice 5v regulated supply
again, my (probably less than) 2c. you know, inflation and all...