SRAM Battery Backup

[beb101]

The question is; do you think this scheme would work with a 20X2,

http://www.edn.com/design/integrated-circuit-design/4335429/Microcontroller-provides-SRAM-battery-backup

And more specifically, powering a 23K256 SRAM from an output pin and retaining the data by switching to power from a CR2032 in the event of power loss.

23K256 datasheet,

http://ww1.microchip.com/downloads/en/DeviceDoc/22100F.pdf

From which,

Supply voltage 2.7V(min) — 3.6V(max)
Operating Current 10mA @ 20MHz (max)
RAM data retention voltage >= 1.2V
Standby current 4µA (/CS = VCC = 3.0V, Inputs tied to VCC or VSS)

A diode-or on V+ and the battery is a standard simple solution and this circuit seems to be the champion,

http://www.picaxeforum.co.uk/showthread.php?8353-Low-Power-Battery-Backup-Reference-Design

On the other hand, the microcontroller scheme requires no extra parts. To forstall the inevitable comment, "why don't you try it?", I managed to kill my last 20X2 and am awaiting parts from Techsupplies. In any event, I am intrigued by the ideas in the cited article, but I know nothing about the innards of the 20X2.

Baxter

 

[MFB]

I would have used FRAM. Can be used like SRAM but is non-volatile. No need to resort to on-board chemistry.

 

[beb101]

Good point ... My brain was locked on to the idea that FRAMs were outrageously expensive, but not so,

http://www.digikey.com/product-search/en/integrated-circuits-ics/memory/2556980?k=fram

The smaller ones are quite reasonable.

Baxter

 

[Buzby]

Hi Baxter,

The smaller ones are cheaper, but they are only in SMD packages.

Can you handle them ?

Cheers,

Buzby

 

[beb101]

Hi busby,

yes, I am trying to transition to SMD parts. I find SOIC pretty easy. I mostly make my own boards to avoid the awful wiring rats nest of breadboarding. The downside of DIY boards is accurate drilling. I've also started skillet reflow soldering which mitigates shaky hands.

Baxter

 

[MFB]

I use the free schematic and layout package from www.expresspcb.com to overcome the 'downside'. Nicely drilled board arrive from US based Express PCB at a reasonable price but there are many European companies that also offer this type of service.

 

[hippy]

The question is; do you think this scheme would work with a 20X2,

http://www.edn.com/design/integrated-circuit-design/4335429/Microcontroller-provides-SRAM-battery-backup

Though we seem to have moved away from that, the answer would be "yes", but it would not generally be recommended and there are caveats and dangers as noted in the article.