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

Roy J. Tellason rtellason at
Wed Jul 2 11:46:36 CDT 2008

On Wednesday 02 July 2008 05:05, Ethan Dicks wrote:
> The dynamic PET, since it has soldered-in DRAMs, is a bit more complicated.
> Unless I care to remove the DRAM and fit another ROM/RAM board for the SRAM
> or adapt a 62256 in some other way, I need +12V and -5V for Vdd and Vbb on
> the 4116 chips.  My question (after all this background info) is... does
> anyone have enough knowledge of the ICL7660 chip to give an opinion on how
> well it would work for supplying -5VDC?  Looking at datasheets, the max
> draw I can find on Intel uP416s is 200uA @ -5VDC (along with all its other
> needs).  It looks like the ICL7660 will provide up to 10mA @ -5VDC, but at
> some higher amount of inefficiency than at lower draws.  16x0.200 is 3.2mA,
> well under the max draw of the ICL7660, so I think I'm OK, but I wanted to
> ask other folks about this in case I'm overlooking some important detail.

That might be workable in terms of current draw,  but that's not what I'd be 
worried about there.  I'm not real sure about the 4116 chips,  but I seem to 
recall that at least some of that early stuff that needed multiple supplies 
needed to have that Vbb supply present _first_ and going away _last_.  It's 
getting it to come up first that I'd be worried about....

> One memory that's filtering up to the surface is that ISTR some
> order-of-DC-powerup requirement for 4116s, like don't apply -5V
> first or remove it last or some such.  I plan to power the ICL7660
> off of the +5V rail, but if there is a very specific order that
> really matters, I might consider running it off the +12V rail
> (with a 78L05 in-between) instead.

Just what I was thinking,  above.  But it's been so long that I really don't 
remember in detail.  It might not even have been the 4116 I was thinking of, 
as there were a bunch of other chips that used multiple power supplies like 
that,  the 2708 coming to mind as well.

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