user67880: 
What is the using purpose of this chip?

user316: There is only one 8-pin SMD IC on the top side of the Arduino Mega 2560.

From the schematic
it appears to be the "LMV358IDGKR" a TI dual op-amp used for two separate functions on the Mega.

Selecting power source - VIN vs USB.
Illuminating the built-in "L" LED (on D13) without loading PB7


67880: <p><a href="https://i.stack.imgur.com/r8b0o.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/r8b0o.jpg" alt="enter image description here" /></a><a href="https://i.stack.imgur.com/GFFvu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GFFvu.png" alt="IC Component" /></a></p>
<p>What is the using purpose of this chip?</p>
 316: <p>There is only one 8-pin SMD IC on the top side of the <a href="https://store.arduino.cc/arduino-mega-2560-rev3" rel="nofollow noreferrer">Arduino Mega 2560</a>.</p>
<p><a href="https://i.stack.imgur.com/y7MS6.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/y7MS6.jpg" alt="Arduino Mega 2560" /></a></p>
<p>From the <a href="https://content.arduino.cc/assets/MEGA2560_Rev3e_sch.pdf" rel="nofollow noreferrer">schematic</a>
it appears to be the &quot;LMV358IDGKR&quot; a TI dual op-amp used for two separate functions on the Mega.</p>
<ul>
<li>Selecting power source - VIN vs USB.</li>
<li>Illuminating the built-in &quot;L&quot; LED (on D13) without loading PB7</li>
</ul>
