Using an ICL7660 to feed -5VDC to 4116 DRAMs?

Dave McGuire mcguire at neurotica.com
Wed Jul 2 12:41:21 CDT 2008


On Jul 2, 2008, at 11:50 AM, Ethan Dicks wrote:
>> There is some loss, which goes up as you load the device;  ie:  if  
>> you
>> drive it from +5.0V and load it lightly, you will get close to  
>> -5.0V, but
>> as you draw more current it will drop down to almost -4.0V.
>
> Right.  That was what I was a little concerned by - 16 DRAMs do add up
> to some measurable current, even at 100-200uA each.  What I wasn't  
> sure
> about is how quickly the ICL7660 drops off in a real application (vs a
> nice clean curve on a spec sheet).

   DRAM chips tend to draw spikes of current during refresh, as those  
little capacitors get charged.  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.

> I've seen mini-switchers like that in the past, 5 lead T-220 package,
> IIRC, but I don't happen to have any handy, and 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.. ;)

         -Dave

-- 
Dave McGuire
Port Charlotte, FL





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