GTA02 Power Glitch Reason Found
andy at openmoko.com
Mon Feb 18 08:33:26 CET 2008
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Somebody in the thread at some point said:
> Dear all:
>> Did these discussions include NXP opinion in the loop?
>> I found that 1uF (I tried it initially) was enough to make a big
>> difference in HF noise >stability on VB_SYS and to deal with short
>> droops, so 4.7uF doesn't sound >completely crazy to me. But it is
>> quite a difference from 22uF recommended by >NXP.
> The 4.7uF is our verification. I think the NXP will reply that we
> must use the 22uF capacitor and I don't want to ask them.The 4.7uF
> just for A5 PVT.
Well, understood I guess... it's an effective way to avoid hearing bad
NXP have to target the chip's worst case load and noise, you only have
to target the A5 worst case, so I guess it can all work out. But its
our problem then to make sure we can switch the worst things around like
GSM / GPS power with 4.7uF and not make a big spike on VB_SYS.
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