consumption in sleep mode

Pierre Adamy

Hi everyone,

I have a question concerning consumption in "sleep" mode.· Does the SX consume less with the pin in input or output direction ? (Of course ouput mode is without load)

This question is for a special application who need to have a very very low consumption (1µa). The SX48 can only be wake up with a MIWU pin, and don't have any special feature active.

Thanks
Pierre
Have nice year-end holidays
·

Bean

I suspect it doesn't make much difference, but if you make them inputs make sure you tie them high or low.
I made this mistake and the current goes way up.

P.S. I don't think you can achive 1uA unless you actually have a circuit that disconnects the power from the SX.

Bean.

Post Edited (Bean) : 12/23/2004 2:16:19 PM GMT

Nate

The couple SX28s that I tested did in fact draw lesss than 1 uA when in sleep mode (with pull-ups resistors enabled on all pins set to input).·

nate

Bean

Wow I would have never guessed it was that low.

I wonder what it would be with the watchdog timer enabled. That would allow battery powered apps that "wake-up" every so often then go back to sleep.

Bean.

Nate

The spec. sheet for the SX says it will draw 10 uA (@3.0V) when sleeping with WDT enabled.· Thus far, I have found the spec. data to be accurate.· (That's why when I measured a current draw of 50 uA when the SX was in sleep mode, I suspected I was doing something wrong - i.e. not setting pull-ups).

Oddly, the spec sheet only shows a maximum current draw when sleeping with WDT enabled (of 110 uA) @ 4.5V, and no typical measurement.· Well, I've always been taught that typical values are somewhat meaningless (there's no guarantee on a 'typical' value).

I love the fact that the SX can sleep without WDT and only draw 1 uA.· Applications that use an externally generated wakeup event use essentially no battery resources while sleeping!

nate

Bean

That's great. I'm thinking of some solar power projects right now.
Bean.

Tracy Allen

A side note on this, concerning brownout and solar or battery powered systems.

-- If the watchdog timer is not enabled and the SX is in sleep mode when the power supply voltage drops below the brownout threshold, then it continues drawing a microamp current during SLEEP. However, if the voltage in brownout stays above about 0.6 volts, the SX does not Reset when the voltage rises back above the brownout threshold. This is in contrast to what happens when the chip is in an operating mode--It does a full Reset after a brownout. This may have consequence on the integrity of variables. In short, the SX chip has no way to know that a brownout occured while it was asleep.

-- If the watchdog is enabled and the SX is in sleep mode also brownout, the power current jumps up when the watchdog times out to levels that exacerbate the battery drain problem--10s of milliamps. The chip does not Reset when the voltage comes back up above the brownout voltage, so the chip has no way to know that this occured. It was in some kind of never-never land. The chip simply resumes the SLEEP mode with low current consumption.

Also keep in mind that Reset is not a low power state. The SX chip draws almost full power when MCLR is brought low--so you can not use an external reset chip to assure that the system will stay in a low power state. The best solution is to be sure that your battery never gets low! Or disable or set the brownout detector to its lowest level. Or use a brownout power cutoff.

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Tracy Allen
www.emesystems.com