AnsweredAssumed Answered

HMC475ST89 Evaluation PCB 116092 Application Circuit Capacitors

Question asked by HMCTemp on Apr 24, 2015
Latest reply on May 5, 2015 by SMcBride



I wish to use an HMC475ST89 as a low-power RF PA and have a question about the application circuit:

What is the manufacturer part number of the 2.2 uF tantalum capacitor C5?


The parts list in the data sheet only specifies component values and package sizes, but not the part numbers of the actual components used for the evaluation board. The capacitor that I find most troublesome is the 2.2 uF tantalum cap, or "C5".

It would appear that L1 combined with C3, C4, and C5 act as a low-pass LC circuit to prevent RF at pin 3 from entering the DC supply line. But in order for this to work, all components must have resonant frequencies greater than that of the RF output.

I plan on using this IC to amplify a 54-MHZ single-side band AM signal, but can't for the life of me find a 2.2uF capacitor that will work at this frequency.


If someone could tell me the part number of C5, suggest an alternate biasing circuit, or at least explain why C4 and C3 are even relevant, I would greatly appreciate it. I have no trouble finding the smaller capacitors for RF, just the large one. It looks like an AVX part, and I can barely make out a "225E" from the eval board pic online.


Thank you!