Playing with ICs
This Cisco Router quit on us. We bought a new router since the kids didn’t want to wait and see if I could fix it. I decided to salvage all of the SMD components that I could use. Finding out that the SOP-8 IC is an 18V, 2A, 340 KHz Synchronous Step-Down DC/DC Converter, I decided to play with it on my Breadboard (BB). I soldered some BB wires onto the leads. Please click on the below to visit the datasheet website:
I re-wrapped the SMD 10uH inductor to make a through-hole inductor out of it with 22cm of 28 gauge magnet wire.
The white 10uH inductor that I have is just too big for my small BB, as you can see in one of the pictures.
My circuit is set up like the top schematic on page 2 in the Datasheet. My new 1/4w 1% resistors came in today, so I changed the resistors in the circuit with the 1% resistors, except for the two that are in parallel in front of the inductor. I don’t have a 26.1K 1% resistor, so I’m using one each of 82K & 39K 5% resistors in parallel which measure a tad over 26K – which is within tolerance. I ordered some 26.1K 1% resistors but they may not get here before I publish this article.
It is supposed to output 3.3V according to the schematic with 4.5V input, but it is outputting around 4V. I started changing the resistor values and it didn’t make any difference.
The DC voltage trace looks pretty clean. The bottom trace is from the power supply, and the top trace is the IC output. I believe that this IC is what caused the router to quit. The CPU shut down because it wasn’t getting the proper voltage. I put the circuit back according to the schematic and raised the voltage up to 12V. According to the schematic in the datasheet, it should handle 18V. Pop! Whatever was bad in the IC gave up the ghost when I raised the voltage up.
When I heard the pop and saw the LED go out, I saw the amps max out at 0.5A on my power supply that it was set to, and the volts went to zero. I touched the top of the IC and it was getting hot. So I shut the power supply off.
I guess play time is over! I wanted to get a new IC to check against this one on my BB, but I couldn’t find one. I checked Mouser, Digikey, and a couple others but none of them even had a listing for this IC. Oh well – on to the next project.
This article was written by Robert Calk Jr. He is an Electronics Hobbyist and loves learning electronics and device repair.
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