GekkoScience BM1384 Project Development Discussion

[goodney]

About the best thing I can think of is it's a layout issue.

Sidehack:

Did you get this figured out? I had a similar problem on one of those TI TPS chips and I never really figured it out. I had to rev the board to fix another problem and on the new rev I did a better job of making the layout match the "suggested layout" in the datasheet. Worked just fine on the new layout... so take that as a my BTC0.02

Good luck!

-a[g

[1714200298]

1714200298

[1714200298]

1714200298

[1714200298]

1714200298

[sidehack]

Well, I can't exactly change the layout on an existing board without getting a new board. And as I said in that post you quoted, immediately after the part you quoted, "If I gotta change the layout in a major way like that it'll mean getting new prototype PCBs which will burn an extra week or two and probably a couple hundred bucks." Since it's been about five days (quite a bit less than two weeks), no I haven't gotten it figured out - or at least, I haven't yet verified that the changes I made to the design actually work yet.

[jstefanop]

Edit: Add to that this rather graphic bit on what can easily happen to an ASIC's power... http://powerelectronics.com/community/why-pdn-measured-using-vna-and-not-oscilloscope?page=1

resistive load step response:

Same load step with just 1 resonant node in the PDN:

Ahh yes I had lots of fun dealing with the transients in my design. At least for the scrypt chip I'm dealing with it was not that bad because the transients occurred at the end of each hash cycle...which for this chip was in the range of 10-20 khz, so even at a 250 kHz switch rate it was manageable and enough spacing to decouple any resonances. Im pretty sure SHA cores have hash cycles in the 100s of kHz, which would be pretty nasty for a 250 kHz buck.