I'm curious about powering Arduino Uno, Raspberry pi 3 b+ and motor driver L298n. I've got 11.1V / 2200 maH li-po battery. Firstly connected battery to motor driver, then feeded arduino from 5V out pin of motor driver. I want to use adjustable regulator to power my rasp from gpio 5v pin. I'm afraid the board will burn. If I feed 5 volts, what is the probability of burning? Are there extra measures to take? Should I give directly 5 volts or by dimming it?
I do not think a typical L298N based motor driver module can supply enough power for the Raspberry Pi.
Its 5V output (derived from its input power) is only designed to provide logic power for the L298N motor driver module itself.
I suggest you buy a UBEC (Ultimate Battery Eliminator Circuit) which will efficiently convert your LIPO 11V to 5V. You could use that to power the Pi and the Arduino. UBECs are not that expensive. For instance look on eBay.
I use a similar set-up with a LIPO connected to a UBEC connected to the Pi's 5V and ground pins.
Arduino Uno has a voltage regulator direct attached to the power jack. It can receive voltages from 5v to 12v volts, recommended more than 6v and less than 13v. So, you can attach the Arduino Uno direct to the LiPo battery.
The Raspiberry Pi 3 b+ has a urge for corrent, it needs at least 1.8A to work, but could easily drag 2.5A depending on what you are doing. As sugested by @joan a UBEC is a good alternative. Or you can use a Step Down voltage regulator. Something like this: https://www.sparkfun.com/products/9370 But before buy it make some calculations of how much power you need.
Motor Driver you didn't specify the type of L298n that you have. There is a bunch of them with different layouts. You need to specify your model and what kind of motor you will drive. Depending on your use it can be connected direct to the battery, to the arduino Uno or even connected to the Raspiberry Pi. It really depends of the motor power consumption and the destination given to the project. It's not a good idea using the 5v pins, from the Arduino or the Raspberry, to power the motor driver. The reason of existence of the Motor Driver is to receive power supply from a battery and receive only signaling from the micro-controller boards. Don't use the Motor Driver as a Step Down ( using the motor driver to power arduino or raspberry).