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

gil smith gil at baudot.net
Wed Jul 2 12:24:22 CDT 2008


At 08:50 AM 7/2/2008, you wrote:
>On Wed, Jul 02, 2008 at 08:14:32AM -0700, gil smith wrote:
> > Hi Ethan:
> >
> > I use the 7660 all the time -- it needs two 100uF caps -- works
> > great!  Can't draw a lot of current, but if the spec fits it is a great
> > solution.
>
>Right.  I've used them before, but mostly for negative LCD bias voltage
>for HD44780-type LCDs - they don't need much current at all (I think I
>was using 10uF caps, but 100uF is no problem to find).

Yeah, it probably uses 10uF in the spec, but we standardize on a minimal 
number of component values, and 100u works just fine, so less unique parts 
to deal with for us -- whatever you have on hand should work for 
you.  Likewise, the 2674 specs a .01 uf feedback cap, but .1 works just fine.

I think one of the 7660's caps sees +/-5V switching for 10V total, IIRC, so 
don't put a 6V part in there.

Also, I think the standard 7660 is good up to about 10V input.  There is a 
higher-volt part that I believe is a 7660S -- should work fine at 5 or 6V 
input too, if that is what you scrounge up from your parts box.


 > Another was to go is to use a real switcher like an LM2674M-5.0, but
> > configured for -5 instead of +5 -- I use this chip all the time too for
> > both pos and neg 5V -- very efficient.  Drive from unreg volage (eg: 
> +12 to
> > +20 or so); you also need a 100uH inductor, a schottky diode, and a few
> > caps.  Pricier, but can efficiently source up to an amp.
>
>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.

The 2674 is an 8-pin dip or soic.  Nice part.  Are you really at the South 
Pole?  4 months to get stuff from digikey?  Must be UPS (underwater parcel 
service).

gil

Ethan Dicks, A-333-S     Current South Pole Weather at  2-Jul-2008 at 15:30 Z
>South Pole Station
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>
>Ethan.Dicks at usap.gov            http://penguincentral.com/penguincentral.html



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