low powering by Idle mode

bertronicom · Posted: Thu Mar 09, 2006 6:16 am

Hello,

I'm struggling to minimize the power in my PIC18f6622 when the PIC hasn't nothing to do.

The normal current consumption of my PIC is 3mAmps withouth Idle mode. When Idle mode is active current consumption down to 2mAmps.

Only 1mAmp?????
I think this is very poor power saving mode. Any suggestion about my code???

Thanks a lot in advance

I did this:

Ttelmah · Guest

How are you measuring the current?. What is connected?.
To get low power, you have to ensure that every output is driving to the state where it draws least power (disabling other circuitry etc.), and that the chip does not itself have to deliver significant power 'into' anything. Also, make sure that inputs to the chip, are not themselves 'floating', but are pulled by external circuitry to the idle state. Remember also, that if you have something like a 5v regulator, _this_ may well draw a couple of mA itself!...
As a 'for instance' of how important the regulator may be, changing from using a 78L05, to a Motorola 78LC05, changed the standby consumption, from 3mA, to 10uA...
On smaller PICs, I'd suggest, taking the PIC out, tying all the pins to the voltages that the PIC is set to hold them, and seeing how much current is drawn. I'd not be suprised if you found most of the current is being drawn in the drives, or other circuitry.

Best Wishes

bertronicom · Posted: Thu Mar 09, 2006 9:49 am

I've meassureed the current with a Fluke multimeter from the external power supply and this current was the whole consumption of my board. The only change in current when I changed to Idle mode was from 4mA down to 3mA.

It seems to me very poor current reduction, isn't it.

All external pull-ups were in the way to not drawn current.
Regulator can't eat 1mA, over 4mA in the board at 3.3v. It could be extremely ineficient.

Ttelmah · Guest

A regulator can _easily_ eat 3mA.
What regulator are you using?.

Best Wishes

Felix Althaus · Posted: Sun Mar 12, 2006 6:33 am

Hello

@ Ttelmah:
About this Motorola 78LC05: I searched Google, some semiconductor catalogues, etc. but I can't find the datasheet or some place to buy a device.
Is this an older part number (RoHS?) or what?

Do you have a link to a datasheet or a similar std. device?

Thanks

Felix

drh · Posted: Sun Mar 12, 2006 10:08 am

Felix Althaus,
the "Motorola" 78LC05 can be found on the on semiconductor web site.
www.onsemi.com
_________________
David

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

I couldn't find the 78LC05 either, but did find the Motorola 78LC50.
I'm not sure this is the same regulator Ttelmah referred to but it is a 3-pin device with a tipycal quiescent current of 1.1uA typical. Only disadvantages to me are that it is SMD only (no TO-220) and has a maximum input voltage of 12V.