Problem powering OMAP-L137 with a TPS650532

Each ground should be tied together at a single point and with no impedance between them.  Your ferrite bead may have several Ohms of DCR, which is far too much to have between ground connections.  Depending on how much current each ground carries, these Ohms of resistance can equal Volts of voltage which could easily exceed maximum ratings of the ICs.  Do you have a schematic you could attach?

For input current, measure how much current the board draws on each of its rails.  Then, see how much power this is at the 6V input.  200 mA is just 1.2W of input power, which is fairly low I would think.  It shouldn't hurt to set your input current limit higher, unless something is shorted on the board.

Oh well. So I just might have damaged the processor with this simple mistake of putting the bead in? Or just the power chip? I did replace the bead with a jumper (that's the only point connecting to system GND) after realizing it might be a bad thing but of course the damage may have occurred on the first power up...

The rails don't draw much, something like 30-40mA from 1.2V and 3.3V on normal power up when there's nothing running on the processor. The 1.8V rail draws even less than that. That said, 200mA from 6V is way more which is sad news. I don't think there's anything shorted on the board although I haven't used this particular board at all before (the lab supplies are used with another one). Before powering up, I measured the resistances between every rail and GND and they were ok.

The schema is quite big and I'm afraid I'm not allowed to show it because it's part of a big project I'm working on. Maybe I could explain the parts you're interested in? Please ask what you want to know and I'll try to give the details.

It depends on what you had connected to each ground.  The current going into, say, the processor core has to return to the source--input ground.  If this ground is separated by resistance from the processor ground, then there will be a voltage drop across that resistance.  This, added to the 1.2V, could overvoltage that node.

To find out what is shorted, turn on the power and see (with a thermal camera or by touch) what gets hot.

The bead is from MURATA and it's specs are

• Typ Impedance @ 100MHz:120ohm
• Max DC Resistance:0.18ohm
• DC Current Rating:500mA
• Resistance:0.18ohm
• Series:BLM18

Nothing feels hot but the resistance from 1.2V and 3.3V to GND is only several hundreds of ohms which most probably means damage. That's really bad because there's little possibility to replace the processor, don't you think? I can remove the power chip to see if the resistances get back to normal but from what you said, I can be pretty sure it's the processor that's damaged. I don't know where I got the idea of putting a bead there in the first place, probably thinking it could suppress spikes. And in this case, it did just the opposite.

Do you think there's even the slightest possibility that the processor could stand the overvoltages caused by that bead?

An over voltage of the processor is just one possibility.  The power ICs might be over voltaged instead/also.  You need to debug the board and see what is damaged.  One way to do this is pumping a lot of power into the board (increase your current limit) and seeing what gets hot.

Ok, I'll debug it a little more. I'm not going as radical as experimental overheating yet because I just might save some of the components on the board. I'll get back when I know more. Thanks a lot for your help so far!

Best Regards,

   Harri

Yes, that could be a good idea. On the other hand, I've managed to test my power far enough to see that all voltages are spot on. I don't think experimenting with the EVM would shed any light to why I'm having spikes and interferences. Did you mean connecting the EVM to my board just like I'm doing with lab supplies now? One useful thing with a test like that would indeed be to see if I'd have cleaner power lines just because the switcher portion is a bit farther from the system board GND/VCC planes. I'll see if I can get an EVM quickly enough to do that test.

There's one clearly suspicious thing about the board. You see, our PCB guy didn't follow the design instructions and there isn't a completely separate ground plane under the power domain. The power domain is placed to the corner of the PCB but the grounds are (thick) stripes going around the switchers and there's even the system ground plane underneath. Do you think this will cause interference problems that are impossible to cure?

Before the current started to rise and I had to switch off,  I remember seeing high voltage spikes on the power rails which exactly followed the primary DCDC-converter output FET pumping. I'm very concerned about this kind of crosstalk but the ferrite bead was present at that time so it could cause some if not all of it.