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LMZ16308 Noise GPS (GNSS)

Joan Navarro
Prodigy 20 points
Other Parts Discussed in Thread: LMZ13610, LMZ13608

Hi,

We have done a design using LMZ16308 voltage regulator for powering a cell phone module Cinterion TC 65 inside a small unit that coexist with GPS (GNSS) receiver RTK high precision. The problem we get is interference in the GNSS signals from internal LMZ 16308 freq. harmonics. We have installed all combination capacitors and inductive filters from documentation and also we produce a metal shield by CNCbut we can't fix the noise. Could you tell us if you have any suggest or another voltage regulator for this application. If we remove the voltage regulator and we power the unit using Tektronics laboratory power supply system works correct. Thanks a lot for help.

Joan

  • 0
    TI__Genius 10095 points

    Hi Joan,

    There are other voltage regulators we could recommend, but let me see if I can help you with your current design as it might be a layout issue which could propogate the problem even with another regulator.

    Would  it be  possible to send the relevent schematics and layout for the part of the system where you are seeing problems. 

    Questions: 

    1)  If you wire in the evaluation board for the LMZ13610/08 in the same manner as you do the Tektronics supply, does the problem go away.  I can have one shipped to you if you need.

    2) In the module layout (looking from the top) the left hand side near the Vin pins is the switch node.  Although the module has reduced the size of this trace significantly, you can still pick up noise if a trace is routed close to this area.  Do you have any sensitive traces routed near this side of the module?

    3) What additional combination of capacitors and filters did you try?  Did you filter the output votlage or the input voltage of the module?

     

    Marc

     

  • 0 in reply to Marc Davis-Marsh
    Prodigy 20 points

    Thanks a lot for the answer,

    We have no LMZ13608 evaluation board also not for the LMZ 14201, same unit use both components.

    I attach the top PCB design and the standard Schematics we use, we reduce the noise conducted adding 5 input capacitor 47uf X5r and 100uf and 10 uf used in the evaluation board and schematics from the components, we get better conducted results but GNSS receiver have problems with Glonass L2 and GPS L2 signals.

    We installed a full aluminum shield that covers the LMZs and full electronics from the GNSS antenna but no really good improve.

    EMI absorber also has been added but also problem is not fixed..

    Also we add the inductive in serial as it is in the evaluation board for LMZ 13608 and then the signals in GNSS receiver is more affected and noise in most reception satellites.

    Thanks in advance

    Joan

    5238.POWER_sch.pdf

    8233.POWER_pcb.pdf

  • 0 in reply to Joan Navarro
    TI__Genius 10095 points

    HI Joan,

    I have a couple of questions

     

    1) Do you have any vias underneath the Die attach pad (DAP) of the modules.  I ask because having ceramic capacitors with vias to ground and a ground plane underneath to connect to the DAP of the part will improve the high frequency performance.

    2)The input and output capacitors are all tantalum.  Were the capacitors you added, ceramic? Tantalum have around 1 ohm or ESR.  This will cause alot of ripple on all of the rails.  Ceramic capacitors will be needed to reduce the ripple on all of these rails.

    3)  When you added the filter, did you follow the filter design used on the EVM?