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TRF7960a attached crystal doesn't oscillate

Serge Malouin
Intellectual 280 points
Other Parts Discussed in Thread: TRF7960A, MSP430F5438A, TRF7960

We have a design using a TRF7960a connected to a MSP430F5438a.

We have a problem with the oscillator. We can se on the TRF7960_EVM_revA as soon as the EN pin is raised the oscillator starts to oscillate at 13.560MHz as anyone would expect.

On our design, when we raise the same EN pin, we simply see ~1.8Vdc on each side of our crystal, but it doesn't oscillate.

We use a Abracom 13.560MHz crystal, with a load capacitance of 18pF and an ESR of 80R.

The reference board as a 13.56MHz crystal with a load capacitance of 12pF and an ESR of 30R on it. (http://www.abracon.com/Resonators/ABM8G.pdf)

Can this be enough difference to prohibit our oscillator from operating normaly?

I am attaching our TRF7960a schematic page, just in case you guys notice something out of the ordinary.

  • 0
    TI__Guru* 91206 points

    Serge - 

    maybe the crystal has load cap requirement of something lower (looking on the generic one in the link you sent over i see 10pF listed)

    you might want to try using two 22pF or two 18pF instead of two 27pF? 

  • 0 in reply to Josh Wyatt
    Intellectual 280 points

    Ok... just in case anybody follows the current thread in the future because of a similar problem:

    The problem was that my 13.56MHz crystal a 4 pad rectangular crystal was soldered vertically instead of horizontally like the silkscreen pad indicates (90°off).

    We had 10 prototype units assembled (by our external assembler, with the real deal, pick and place, reflow oven, the whole thing!), and they all arrived like that.

    sigh...

    S.