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TPS61099: Avoiding switching noise leakage

Valentinas Pancerovas
Intellectual 410 points
Part Number: TPS61099

Hi,

I will be using TPS610993YFFR and TPS62840YBGR in my design and since its a very tight design i am trying to fit them in properly so they dont induce noise into my circuit.

I have chosen to use MEKK2016H2R2M inductor for both chips, i needed low ESR so i had to go for this fairly large inductor.

I dont know how close i can put other PCB components around these two chips and the inductors in order to have a noise free design. Do you have any specific recommendations? For example do i need 0.5mm clearance? Or maybe 1mm or more ?

Thank you,

Valentinas

  • 0
    TI__Mastermind 21565 points

    Hi Valentinas:

    Thanks for choosing TI parts. The clearance I use usually 6mil for lines and 15 mil for component to IC. The purpose I use 15 mil is because we need to debug in lab some time with manual soldering. If you don't have this need, 10 mil is OK. Actually, it mainly depends on the PCB and soldering production. You could ask them for suggestion. 

    For reduce the noise, there are some application note:

     http://www.ti.com/lit/an/slva790a/slva790a.pdf

    http://www.ti.com/lit/an/slva255/slva255.pdf

  • 0 in reply to Minqiu Xie
    Intellectual 410 points

    Thank you Minqiu,

    These links were helpful even though they are solving problems that occurred in very powerful switching systems compared to mine so hopefully mine dorsnt have such issues. I liked the small close cap idea and rc snubber.

    It would be very interesting if TI made radiation patterns in real picture forms for each of the IC that they sell so we could cherry pick the ones that may look best for sensitive systems. My PCB is less than 3mm in diameter so I try to save all the space I can

  • 0 in reply to Valentinas Pancerovas
    TI__Mastermind 21565 points

    Thanks for your kind words, Valentinas. I will share your views with my team.

    And in my opinion, not all customer need to consider the noise, and some solutions will increase the cost (Ferrite beads) or decrease the efficiency (Snubber) . And the performance is related to the layout closely.

    May I know what your application is and why you so care about the noise?

  • 0 in reply to Minqiu Xie
    Intellectual 410 points

    Hello again Minqiu,

    The application is a wearable device that uses a CR2450 battery and antennas are all around the PCB because we have 3 of them which leads me to having only 25 mm diameter of usable space. The most power consuming chip needs 150mA for very short intervals but the battery cannot supply that much so i have to put big capacitors to be able to feed that current into the chip. Therefore the PCB is very tight in space and these two buck/boost converters need to be taken care of. I have personally not used them before so i have no idea how much they radiate but i am not really too worried about it.

    http://prntscr.com/q2sw1g  I could not upload pictures so i here is a link to the screen shot. As you can see big capacitors are close to the regulators but i tried to separate them by having alot of GND vias, Antenna is peeking out on the right aswell and its quite close to the buck converter but hopefully they dont interfere with each other.

  • 0 in reply to Valentinas Pancerovas
    TI__Mastermind 21565 points

    Hi Valentina:

     For wearable device, the TPS61099 is really a good choice with low Iq and high efficiency. And it has been already used in lot of customers with good performance. 

    Take care about the layout, and make sure the Vout-Cout-GND routing as short as possible to reduce the parasitic parameters. It's a easy way to reduce the noise but very important.