Two quick question...
Is it true that the ATmega328 (DIP) chip can only work with 5V?
And that ATmega328 (QFP) chip can work properly with 3.3V?
I need the second chip (QFP) since based on what I researched, it can work with 3.3V and is perfect for my project (this chip is square and flat).
Can you confirm if what I said is true?
Thanks!!!
Atmega 328P Data Sheet:
https://www.mouser.com/pdfdocs/gravitech_atmega328_datasheet.pdf
Operating Voltage:
1.8 - 5.5V for ATmega48PA/88PA/168PA/328P
Square and flat is just the package.
Read the data sheets for the exact chips you have in mind.
Ron
The DIP will run fine at 3.3V, but not at 16MHz, you will need to drop to 8.
The 328 is available in different packages.
Makes no difference to the functionality.
If you run the 328 on 3.3volt, then you must drop the clock speed to 8Mhz.
16Mhz and 3.3volt is out of specs (undervolting is overclocking), and weird things could happen.
Maybe easier/cheaper to use a 3.3volt ProMini in your project.
Leo..
I have tried Arduino Pro Mini on 3.7V but its doesn't work properly, I have to add a capacitor of 1000uF and it worked like charm.
jackthomson42:
I have tried Arduino Pro Mini on 3.7V but its doesn't work properly, I have to add a capacitor of 1000uF and it worked like charm.
Did you really mean 3.7V or were you using a Lithium battery that could be anywhere between 4.2V and 3.0V ?
Arduino Pro Minis, the 8Mhz ones, are very relaible when run at 3.3V, minimal capacitance required, most Pro Minis olny have 10uF capacitors fitted.
These microcontrollers have a brown-out detector circuit that can be programmed with fuse bits. Standard
Arduino bootloaders set the brown-out voltage as 2.7V so unless you alter the bootloader settings you are limited
to the range 3.0V to 5.5V. A brown-out circuit prevents random behaviour on supply voltage droop, it activates
a hard reset state before the chip misbheaves.
At 16MHz the chip isn't guaranteed to work much below 4V, although many will work at 3.3V (you are pushing
your luck!). The datasheet has a graph of max clock speed v. supply voltage.
The package is TQFP-32 (not QFP), the extra 4 pins break out A6 and A7 as well as two more power/ground pins.
The 3.3V Pro Mini works fine on 2xAA batteries even. The package of the chip itself doesn't matter...
pozole:
I need the second chip (QFP) since based on what I researched, it can work with 3.3V and is perfect for my project (this chip is square and flat).
Sounds like you're trying to design your own PCB.
Don't forget the ISP header as the chip won't come with a bootloader installed, which is needed for programming over the Serial interface, and the other required components (such as the decoupling caps, pull-up resistor on RESET, external crystal if you want).
wvmarle:
Sounds like you're trying to design your own PCB.
Generally silly idea.
Make a PCB by all means, Use a Pro Mini of the appropriate voltage as a daughterboard.
(Unless you want to make thousands and have it fabbed in Wuhan. 
)
I'm building PCBs quite regularly - and stopped using the Pro Mini as daughterboard to save work. It is so much easier and quicker to just drop an TQFP chip on the board and use some hot air than it is to hand solder 30 pins on two sides (the pin header to the board and to the Pro Mini)! Oftentimes using the ATtiny84a, that's a tiny SOIC8 package, but lately trying to move on to the 0 and 1 series ATtiny.
Cost wise it's also not that bad, really. 10 pcs PCB max 100x100 mm plus stencil & shipping costs me about USD 18. Bare chips save a lot of space on the board, and still cost a little less than the Pro Mini itself.
Also sad that there's still no Pro Mini with the ATmega328PB on board: a few more I/O pins, second hardware Serial, more timers, and significantly cheaper even than the ATmega328P... good stuff.