3 Jul
2008
3 Jul
'08
9:57 a.m.
On Jul 2, 2008, at 1:48 PM, Ethan Dicks wrote:
I've only worked with 41256s design-wise. We used 8207 DRAM
controllers, which were great in terms of functionality, but good
heavens did we have problems with noisy power on those boards. I
never want to go through that again. Those refresh spikes had such
fast rise times (in ca. 1987 terms) that short, low-inductance paths
to the bypass capacitors within the DRAM array turned out to be very
important.
I just mean putting some decent bypassing electrically close to
the board; presumably there are already a reasonable number of bypass
capacitors in the DRAM array. Steven Canning said the supply that's
affected worst by refreshing is +12V...I didn't know that; if that's
the case then you shouldn't have to worry all that much about
bypassing -5V anyway.
Yes... ;) indeed.
:)
-Dave
--
Dave McGuire
Port Charlotte, FL
DRAM chips
tend to draw spikes of current during refresh, as those
little capacitors get charged.
Sure... I'm used to that with +5V-only chips like the 4164 and
up, but I don't have any design experience with the multi-voltage
parts, thus my caution. If you have
adequate low-impedance
bypassing to supply those short-term demands, things should be fine
with the 7660. It's a fairly predictable and dependable chip.
By low-impedance bypassing, you mean monolithic (not electrolytic)
caps,
or do you mean something else? ... I wouldn't be able to get an order from
Digikey for nearly 4
months in any case. I have to use what's on hand.
Good heavens, one would think you're in Antarctica or something.
Oh, wait.. ;)