Hardware question on F vs LF

alan · Joined: 12 Nov 2012 Posts: 357 Location: South Africa

Goodday

I am battling to understand the the difference between 16F and 16LF.

Using PIC16F1829.
According to datasheet the operating voltage on F are 1.8 - 5.5V and LF are 1.8 - 3.6V (Easy to grasp)

The max Frequency on both chips are 32MHz for 2.5V and up to max. (On some PIC's I know the max frequency differs between the F and LF)

So are there any reason why I can't use the PIC16F with a Vdd of 3.6V?
Would there be any drawback?

The only difference I could find between the two are the POR (0.8 and 1.5V) and the RAM Data retention(1.5 and 1.7V) voltage
Have plenty of PIC16F1829 stock but need Vdd of 3.3V.

Sorry for the OT question.

Regards

temtronic · Posted: Tue Jun 19, 2018 4:47 am

I can't see any reason it won't work, makes me wonder why the LF version was designed and made. Though Microchip does make special or specific devices for clients,then makes them available for all to buy.
I usually use the 18F46K22 at 5 volts, but it's quite happy to run at 3. Few years back, I decided to look for a 'Swiss army knife' PIC and chose the 46k22. One of the reasons was the wide range of VDD.Good for old school 5 volt stuff, easy to interface with 3V peripherals.

I'll ask a follow up query.
Why can't the same device header be used for F AND LF versions of PICs? Wanted to play with a PIC16F1829 but the version of the compiler I have only has the PIC16LF1829.h? Found that out after I'd ordered the PICs,DOH !

Jay

alan · Joined: 12 Nov 2012 Posts: 357 Location: South Africa

Ok, I'll byte what doesn't work by compiling with the LF header.

I use a dsPIC33EP128GM304 and a dsPIC33EP128GM604 on the same board, depends on which one are cheaper when I buy.

I compiled with the 604 header and program both versions with the same hex file. Three years later still had no comeback with this arrangement.

Regards

temtronic · Posted: Tue Jun 19, 2018 5:18 am

OK, just tried it again..it does compile BUT I can't download into the PIC ! Sorry, I knew there was a problem and gave up maybe a month ago. Using MPLAB 8v92 / PICkit3. when it didn't work, went onto other projects....
I thought it might have been MPLAB 8v86, downloaded 92, installed it, got upset cause it 'wiped out' reliable 86. I wrongfully assumed I could have both 86 and 92 available...arrgh... so I gave up for a bit.

I know there's a 'stand alone' pgmr code somewhere just haven't had tome to find/install/test...
Jay

alan · Joined: 12 Nov 2012 Posts: 357 Location: South Africa

Aaah. Yes you can't use MPLAB IDE.
I use MPLAB IPE to do the programming with PicKit3, which allow me to specify the chip regardless what the code originally used.

Regards

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

alan · Joined: 12 Nov 2012 Posts: 357 Location: South Africa

Thanks PCM for that clarification. At 1st glance I didn't pick up that there are actually 2 tables combined in one. Must admit it took me about 3 min to see where you got your information from.

I am not critical for current so I can use the F version, but at least now I understand the difference between the two.

Got a 12V 200Ah battery connected, so I am happy with 20.5uA sleep Very Happy

Ttelmah · Joined: 11 Mar 2010 Posts: 19498

Yes it's an interesting 'pair'. In most cases the LF version supports higher clock speeds at the lower voltages. In this case it doesn't. For voltages above 2.5v (which is what you are using), the only downsides visible are the power ones, and (obviously) quicker loss of data on a brownout (2.5v is also the minimum on the F for EEPROM and flash memory operations).
There are similar differences to the one PCM_Programmer pointed out, on the LP & LF oscillator mode power consumption's (36uA versus 9uA). On faster modes the difference drops but is still there (nearly 50% more at 500KHz). The LF in this case is optimised for lower consumption at lower clock rates, and for the basic peripherals (look at the watchdog timer consumption for example - 0.8uA versus 29uA at 3v!...). The FVR draws about 3* as much, The brownout circuit the same, etc. etc..

RogerM · Joined: 07 Jun 2004 Posts: 10

My application has all 3 volt parts, including a LCD and a LoRa radio, I have a voltage regulator on the LiPo battery source. If I have an F PIC it will put 5 volts into the circuit when I do in-circuit programming, it may damage the 3v parts or require additional circuitry to protect them. With a LF PIC that is not a problem.

Roger

Ttelmah · Joined: 11 Mar 2010 Posts: 19498

Why?.

That is down to the voltage programmed to be used by your ICSP system, not the PIC. The F (in the case of the chip being talked about here), still supports full program and erase down to 2.7v. If you select 'unit supplies power', there is no more voltage put into the system than the board's supply generates.

blowtorch · Joined: 11 Jun 2013 Posts: 35 Location: Cape Town

Alan, further to comments regarding the differences above, I have used both F and LF versions and both operate just fine at lower supply voltages. I have several dev boards with the F version and these even start up from sleep powered from 2 tired old AA batteries with the supply coming in via a Schottky.

RogerM · Joined: 07 Jun 2004 Posts: 10

Thanks for the information, I guess it shows I need to read the data sheet better. I remember trying to use a lower voltage quite some years ago on a different PIC and it not working.

So in this case the only advantage would be the lower sleep power.

Roger

Ttelmah · Joined: 11 Mar 2010 Posts: 19498

Yes.
It definitely is a 'read the sheet' one. On a lot of PIC's the LF version supports much faster clock operation at lower voltages. So (for instance), on the 18F45K50, the LF supports 20MHz at 2.7v, while the F only supports 4Mhz at the same voltage!. interestingly on this one, there is no difference in the current consumption between the versions, it is just specified in terms of supply voltage, clock rates, and what modules are enabled.
Then you get a second 'type', where the LF version doesn't have the internal regulator (a lot of the chips with a lower voltage 'core'), and on these the regulator part is shorted out, and putting the LF onto a higher voltage can destroy the chip...
Then you get the third type like this one, where it appears they may have actually used a narrower internal geometry to the die, lowering the maximum voltage that 'can' be used, and the power consumption at the lower voltage. However Vddmin, is the same for both versions.

There is a potential programming issue with both chips. On modern programmers Vpp is programmable. However old devices like the ICD2, have a fixed Vpp, which is above the voltage supported by both types of these chips. So in the data sheet there is a warning: