Difference between PIC LF and PIC F?

[Mr RB]

Hi, does anyone know the actual difference between a PIC LF and F version?

Say between a 18F452 and 18LF452? The data sheet shows everything pretty much identical except the LF version has a chart showing oscillator zone being ok at lower voltages.

I'm interested in the exact reason one part is F and another is LF? Is the LF manufactured differently, and if so what are the differences?

Or did the LF part just go through an extra test to check it was ok running at lower voltage and then got marked as LF?

The reason is that I need a couple of PICs to run from 3.0v (hobby project) and don't have any LF parts in stock at the moment and they take 14 days to get here and cost me shipping etc.

Also if anyone has real world experience using a F part at 3v Vdd or anything like that it would be nice to hear from you.

 

[Nigel Goodwin]

I've always presumed that the LF series are exactly the same, but are 'perhaps' selected for low voltage working (but perhaps not even that).

I've used numerous F series fed from two AA batteries, and they have always worked perfectly.

 

[Pigskin Tony]

A few seconds of searching. At Microchip found this:

GIn lower pin count devices, such as the PIC18F45J10 (see Figure 2), the “F” designation in the name (i.e., PIC18F45J10) specifies that the internal voltage regulator enable is always tied to VDD and the regulator is always on. The “LF” designation (i.e., PIC18LF45J10) specifies that the voltage regulator enable is always tied to ground and that the regulator will always be disabled.

This was found in Migrating from PIC18F to PIC18FXXJ Flash Devices

Don't know if it applies to all LF devices but it goes to show it's more than clever marketing.
.

 

[Nigel Goodwin]

A few seconds of searching. At Microchip found this:



This was found in Migrating from PIC18F to PIC18FXXJ Flash Devices

Don't know if it applies to all LF devices but it goes to show it's more than clever marketing.
.

I think it's only in that series, the lower end devices don't have regulators.

 

[DirtyLude]

The 16F193x devices I'm working with have regulators as well. I think all the enhanced cores run at low voltage and the F series just has a regulator in them for the core only. They do this with ARM chips as well, since the core runs at 1.8v and the peripherals are at 3.3.

The 16F193x series actually wants a bypass cap on a couple of the input pins specifically for the regulator. You can choose the pins with the fuses.

 

[be80be]

The j chips are a whole new ball game. But say you pick a 18f1230
And you get 10 of them 5 or more will run fine at the Lf voltage
Levels . Always made me wonder if they just checked there chips
in to see if they stay in spec. At lower levels.

PS I've run the 18f1220 with built in Osc and the the 18f452
With a 4 MHz crystal at 3 volts and they ran fine.

 

[Mr RB]

Thanks everyone for the replies! I'm sure the J series (and some new enhanced PICs) are different as their LF models are specced to run at 1.8v.

I had a vague memory from the old days that the F and LF parts were the same silicon, but the LF had passed some additional testing.

This is just a case where I need a couple of standard 40 pin F PICs to run from 3.3v and did not want to have to order some 40 pin LF chips in. Based on Nigel and be80be's results I feel confident enough to just give it a go with the chips I have and see what happens.