schottky diodes as gates, feasibility?

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#1
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Hi all:

I need to know if it is feasible to use schottky diodes (like BAT54) as gates to /CS a sram memory

I'm in a design with an ATXmega128A1 and like to use a dual CA diode with one cathode tied to the /WR signal, the other to the /RD pin, the common anode to the sram /CS and from this node a pullup resistor to VCC, so every time the sram is accessed is also selected
The sram is this
http://www.issi.com/pdf/63LV1024...

The power comsumptiom with the chip deselected is very low, and since this design will have a handheld (and therefore battery powered) variant, I don't like to have the sram selected all the time (/CS to GND) sucking +- 80mA. And also don't like to add a single packaged AND gate to do this work.

Notice that I simulated this circuit and it showed no additional delays, at least not significative delays, which makes this approach attractive. The crystal I'm gonna use is 14.7456MHz

Any experience?

Thanks in advance
Nachus

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How about Fairchild Tinylogic?

http://www.fairchildsemi.com/products/logic/tinylogic/

Diodes used to be used for logic, a long time ago. Amplification was needed, hence diode-transistor logic.

Leon Heller G1HSM

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For low power solutions a schottky diode may not be a wise choice as they can have significant leakage. As Leon suggests, a gate might be a better solution. You need to be careful of power up/down glitches that can wipe the data in the ram, so you might want to use a specific part to manage the power down of the chip - dallas/maxim have such devices. Be sitting down when you see the cost, but they do work well.

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Kartman wrote:
For low power solutions a schottky diode may not be a wise choice as they can have significant leakage. As Leon suggests, a gate might be a better solution. You need to be careful of power up/down glitches that can wipe the data in the ram, so you might want to use a specific part to manage the power down of the chip - dallas/maxim have such devices. Be sitting down when you see the cost, but they do work well.

Actually, the design is not intended to preserve data in SRAM when powered down (only when the controller is powered up, but not accessing the external SRAM, or set to PD or some other low power mode)

The purpose of the diodes is to make the memory "go stand-by" when not accessed for RD or WR

Quote:

How about Fairchild Tinylogic?

http://www.fairchildsemi.com/pro...

Diodes used to be used for logic, a long time ago. Amplification was needed, hence diode-transistor logic.

That's what I wanted to avoid!
But now that you mention it, the prices seems very interesting, at least for reel quantities

Thank you
Nachus

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I would not use diodes there. I would use logic gate.