Dec 27, 2020

Tiny transformer inside: Decapping an isolated power transfer chip

Posted by in category: computing

I saw an ad for a tiny chip 1 that provides 5 volts 2 of isolated power: You feed 5 volts in one side, and get 5 volts out the other side. What makes this remarkable is that the two sides can have up to 5000 volts between them. This chip contains a DC-DC converter and a tiny isolation transformer so there’s no direct electrical connection from one side to the other. I was amazed that they could fit all this into a package smaller than your fingernail, so I decided to take a look inside.

I obtained a sample chip from Texas Instruments. Robert Baruch of project5474 decapped this chip for me by boiling it in sulfuric acid at 210 °C. This dissolved the epoxy package, leaving a pile of tiny components, shown below with a penny for scale. At the top are two tiny silicon dies, one for the primary circuitry and one for the secondary. Below the dies are two magnetized ferrite plates from the transformer. To the right is one of five pieces of woven glass fiber. At the bottom is a copper heat sink, partially dissolved by the decapping process. 3.

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