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ADS54J20EVM: power 3.3V of ADS54J20EVM

suy
Intellectual 995 points
Part Number: ADS54J20EVM
Other Parts Discussed in Thread: LMK04828, TPS82085

Hi Jim,

    I bought the ADS54J20EVM last week,when i debugging i found no AVDD3.3 and 3.3VCLK..After circuit check i found the U12 was no power input and the U11 was not pasted on PCB,there was a ferrite bead instead.So the LMK04828 didn't work until i switching in 4V to the U12,am i doing these is right and why did not paste the U11?

  • 0
    TI__Mastermind 18065 points

    Suy:

    I don't think that what you are seeing on U11 is a ferrite bead...it just looks like one.  The part is a TPS82085 which is a DC-DC module.  The switching supply inductor is on top of the part; the inductor obscures the rest of the IC and it does look like a ferrite bead.

    If there is no 3.7V on the output of U11, then your debug may be correct in that the TPS82085 device is damaged.  All units are tested after assembly but it is certainly possible something was damaged in the shipping process or damaged with an accidental over-voltage or ESD event.  You can also visually inspect the solder connection on the devices around U11 for any damage or insufficient solder; there could be a weak solder joint that opened during shipping.  You may also pursue a return and replace if you want to go down that route.

    Otherwise, you approach to supply an external 3p7V (or thereabouts)  is reasonable.  Generally, I am nervous about tacking the external voltage at the location depicted because the existing device is still in place and may be unintentionally loading down the circuit.  There is not a convenient place to break the circuit there.  Conceivably you can remove U11, R80, and R81 and then safely inject the voltage to both subsequent LDO from there.  Alternatively, you can remove FB13 and FB14 and supply two different external voltages at those nodes.  In short, if your hack works to allow the ADC device to function, then it should be OK.

    --RJH

  • 0 in reply to RJ Hopper
    Intellectual 995 points

    RJH,

        OK,i got it.

         Many thanks for your patient answer!