RE: Tini400 : ISSI memory power consumption

	Although, as Bruce mentioned, low power and high speed tend to be mutually exclusive, this may become less so in the future. Brillance Semiconductor plans to release a low power SRAM with access times at the 25 ns point. While this is far from the 10-12 ns needed to run the DS80C400 at 75 MHz, it is a step in the right direction. Current low power SRAMs are now typically at 55 to 70 ns.

Mike

-----Original Message-----
From: Bruce Boyes [mailto:[email protected]]
Sent: Thursday, April 29, 2004 11:59 AM
To: Vivian de Meillon; tini-6tN4nzCoH/[email protected]
Subject: Re: [TINI]Tini400 : ISSI memory power consumption


At 11:45 PM 4/28/2004 +0200, Vivian de Meillon wrote:

>I need to confirm something. Can someone assist me.
>
>The SRAM, IS61LV10248 ; 1Mx8 10ns. I use 4 of them. I need to confirm
>the normal operating current, in mA(milli-amps) of this device as well
>as the maximum current needed at full operation. The datasheet say it is
>round a 100mA commercial. It is so high. Can it be? I'm very skeptical
>there and want to make sure what it is! Comparing too other
>manufacturers of SRAM, this memory has the highest operating current of
>them all (according to their datasheets). But this memory is probably
>one of the fastest you can get.

I don't understand your question. If you have a doubt about a vendor 
component, you should ask the vendor. They are the only ones qualified to 
make statements about their specifications.

To partly answer your general question, *all* high speed SRAMs use a lot 
more current than low-speed, low-power SRAMs. Why is this surprising to 
you? If you move charge packets around an IC faster then you must charge 
and discharge capacitance faster. I = C Dv/Dt, right? As Dt becomes 
smaller, what happens to I? It must increase (assuming Dv and C are 
constant and for SRAMs of the same geometry and power supply, they are).

If you compare the same speed of SRAMs you will find them all very close to 
each other, whether you compare similar high- or low- speed SRAMs.

>The one's that is being used on the TINI400 module, HM62W8512B from
>Hitachi, uses 45mA max.

This is not even close to being the same part. Much slower.

You can't battery back high speed SRAM, either. Well, I suppose you could 
if the battery is big enough. Low-power and high speed are impractical to 
achieve in the same device.

If you really need low power devices (which you imply) then you cannot use 
high speed components.

Do you have an experienced hardware engineer near you that you can consult?

Bruce

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