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LM2673S-5 Eval Board limited to 16V Input

George Ioakimedes
Genius 4950 points
Other Parts Discussed in Thread: LM2673

I pulled out an old eval board for the LM2673 and for some reason once I increase the input voltage to above 16V the output starts to increase above 5V and increase as the input voltages increases (above 6.5V output). For testing right now this is under a no load condition on the bench.

I've changed the input capacitors as well as the output and the condition stays the same. I'm a little puzzled why this magic 16V threshold is happening and thought I'd make this post to see if anyone was watching this thread on a Sunday and could give me some clues.

Right now I have a 22uH inductor on the output coupled with a 100uF tantalum cap on the output. I was hoping to just make something real quick that we can use today but now I'm stuck scratching my head!

  • 0
    TI__Expert 4365 points

    Hello George,

    (Sorry I wasn't watching the forum yesterday.)  This is probably an issue with minimum load for that EVM.  SInce the application circuit is not under load, there is an issue present that as switching cycles occur, there is more energy transferred to the output than required and it results in the output voltage rising. Switching cycles are requred in order to keep the boost capacitor charged.

    Alan Martin    TI- SVA

     

  • 0 in reply to Alan Martin
    Genius 4950 points

    I tried a couple of combinations of inductor and output caps (I think 68uH and 100uH is what I found laying around) but no combination changed this magic 16V threshold which I found rather odd. At one point I did add a 16 ohm resistor on the load but I believe that just dropped the output down to 0V. I didn't get it working and had to leave but it's now bugging me why it wouldn't work.