I have chose PCF8545 LCD driver to drive my LCD Panel of 78 characters each with 14 segments. My LCD has 15 COMMON and 78 segments pins. As PCF8545 has 8 Common and 40 segments pins, I should use 2 PCF8545 to drive my LCD. But I read in datasheet that "320 segments driven allowing: up to 20 14-segment alphanumeric characters". Now, as my LCD has 78 characters, I think 2 is not enough and I must use 4 numbers of PCF8545.

Has anyone used this PCF8545?

Look to see if NXP or some other manufacturer has app notes showing the use of more than 4 backplanes.

I haven't put together an LCD and a driver, but I kinda know what needs to get done.  It looks like that part multiplexes four backplane pins with four segment pins, so if you want eight backplane pins you only get 36 segment pins.

If I were designing for something with a low production volume (less than 1000 a year or so) and that didn't have serious size or power constraints that ruled it out, I'd seriously consider just using four driver chips to make things easy.  It makes sense to spend a lot of engineering time if you can amortize it over lots of units, but at 1000 a year and a 2-year ROI, scraping 2 $1 chips off the board only earns you $4000, and that doesn't pay for much dinking around.