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PCB Layout Review

David Vincenzi
Prodigy 30 points
Part Number: TPS62808

Tool/software:

I'd like to use 2 TPS62808's, one at 1.8V and one at 3V, to power my small sensor board. I have a 4-layer board with top 3 layers as GND and the bottom as power and singal. It has a size constraint of 42mm. My primary concern is RF and power performance.




I've selected the following components for the Cin Cout and Inductor.
Cin 4.7µF - https://www.digikey.com/en/products/detail/murata-electronics/GRM035R60J475ME15D/5877393
L 1µH - https://www.digikey.com/en/products/detail/taiyo-yuden/MCEE1005T1R0MHN/10231779
Cout 10µF - https://www.digikey.com/en/products/detail/murata-electronics/GRM155R60J106ME15D/5877401
Rvsel - https://www.digikey.com/en/products/detail/yageo/RC0201FR-07133KL/5280255

My main questions are:
- Am I making any big mistakes in the layout?
- Will the placement of the 2 inductors or both power lines interfere at these distances?
- Is Cin close enough to the TPS62808?
- I saw in the datasheet the forced PWM mode will reduce RF interference but I'd like to know if I can just use the normal operation? Below is a screenshot of the TPS62808 in relation to my antenna keep out area. Not sure if it would be possible to guess on if there would be performance issues just from the screenshot. The TPS62808 is about 7mm away from the antenna.



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  • 0
    TI__Mastermind 22080 points

    Hi David,

    thanks for using E2E.

    I was fully loaded today. I will check and provide feedback tomorrow.

    Best regards,

    Andreas.

  • 0 in reply to Andreas Mueller
    Prodigy 30 points

    Thank you very much Andreas

  • +1
    TI__Mastermind 22080 points

    Hi David,

    I did not see any big mistake in your layout. The main current paths could be further optimized by making them as wide as possible for lowest impedance (see layout example in section 8.5.2 of the datasheet).

    It is hard to say if the inductors interfere at this distance. It depends also on the inductors. It is good that you have chosen shielded inductors and that the inductors are rotated by 90° to each other.

    I think Cin is close enough to the TPS62808.

    The forced PWM mode has the advantage of more or less constant switching frequency for all load conditions, whereas the PFM operation reduces the switching frequency at light load (compare figure 8-20 and 8-22 in the datasheet). The voltage ripple at constant switching frequency is better controllable if necessary, for example by additional filtering. But PFM mode has higher efficiency than forced PWM. I can not guess if the distance to your antenna is enough. If it is a loop antenna, operating in the similar frequency range, then there might be some interference.

    Additionally I would suggest to use some bigger input capacitance (≥10uF) for your battery powered application, as recommended in section 8.2.2.4 of the datasheet.

    Best regards,

    Andreas.

  • 0 in reply to Andreas Mueller
    Prodigy 30 points

    Hi Andreas,

    Thank you so much for you time. I will implement these changes and will do some testing on the rest.