I guess they're companies you might not hear a lot about if you don't deal with designing electronics but if you do they're all over the place. You probably have at least a dozen components made by these companies within one meter of you as you're reading this message.
If you want practical examples of what they do, go to digikey.com, search for the company names and click randomly on one of the thousands of hits.
If you want practical examples of what they do, go to digikey.com, search for the company names and click randomly on one of the thousands of hits.
Here's a microcontroller: https://www.digikey.com/product-detail/en/maxim-integrated/M...
Here's an I2C temperature sensor: https://www.digikey.com/product-detail/en/maxim-integrated/M...
Here's an RF amplifier: https://www.digikey.com/product-detail/en/maxim-integrated/M...
Here's a 3v3 DC-DC: https://www.digikey.com/product-detail/en/linear-technology-...