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

Scanning steven.alan.canning at verizon.net
Wed Jul 2 20:13:22 CDT 2008


Ethan,



According to the Motorola datasheet - " All voltages referenced to Vss ( 0V)
and Vbb ( -5 Volts ) must be applied before and removed after other supply
voltages ".



What exacerbates things is that the current spikes from all the chips are
perfectly lined up during the RAS* cycle, but the biggest hit is on the Vdd
line ( +12 Volts ). If they don't already have a 0.1 uFd across each chip on
the Vdd I'd add one. I agree the 7660 should be okay on the - 5 Volts.



Also, don't think these will run at -63 C ( ha ha ha ).



Stay warm, Best regards, Steven





> On Wed, Jul 02, 2008 at 01:41:21PM -0400, Dave McGuire wrote:
> >   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.. ;)
>
> Yes... ;) indeed.
>
> -ethan
>
> --
> Ethan Dicks, A-333-S     Current South Pole Weather at  2-Jul-2008 at
17:40 Z
> South Pole Station
> PSC 468 Box 400       Temp  -81.9 F (-63.3 C)   Windchill  -121.1 F (-85.1
C)
> APO AP 96598          Wind   10.8 kts Grid 46   Barometer 680.7 mb (10602
ft)
>
> Ethan.Dicks at usap.gov
http://penguincentral.com/penguincentral.html




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