Xtal speed vs PIC power

[flotulopex]

Hello,

I'm using a PIC 16LF88 because of it's low voltage ability (my circuit is fed by 2x1,5V batteries).

Looking at the Oscillator's Configurations section in the datasheet, I can't find any info about different Xtal speeds according to which PIC 16F88 or 16LF88 is used.

But when I get to the Electrical Characteristics, I can see this and it confuses me.
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=3837&stc=1&d=126198742 0">

Shall I understand that the LF version of this PIC will not support a Xtal higher than 10MHz?

[Melanie]

If you're running from 2 x 1.5v Batteries, even 10MHz is not guaranteed once your Terminal Voltage starts falling... I'd run it at 4MHz.

[flotulopex]

Thanks Melanie.

I'm running the PIC with a 8MHz Xtal anyway.

IMHO, the fact that this PIC does not support an Xtal over 10MHz should be mentionned in the Oscillator Configuration chapter (or maybe I can't see it).

This could save some time searching why things don't work the way you think they should

[BrianT]

I routinely use 18LF4620 parts at 5 volts and get full crystal speeds up to 10 MHz with the internal PLL giving 40 MHz operation. No troubles. I have always regarded the LF tables in the datasheets as showing the MINIMUM voltage limits whereas the MAXIMUM voltages remain the same as the regular 16Fxx or 18Fxxx parts.

HTH
BrianT

[flotulopex]

I'm comparing two versions of PIC16F1827 and 16LF1827.

I can't really find "big" differences but some VDD & VDR levels.

Why would anyone buy a LF model if it is not only for the gain of 0,2V for minimum RAM retention voltage?

[Bruce]

Why would anyone buy a LF model if it is not only for the gain of 0,2V for minimum RAM retention voltage?

Because some LF versions will work at significantly lower operating voltages.

Consider something like a PIC18LF2431 which will work at 2V with up to a 4MHz
oscillator. The non LF version requires 4.2V minimum for any oscillator speed.