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TPS62140 EMI failure, PVIN and AVIN pins

Ellen Fissel
Prodigy 10 points
Other Parts Discussed in Thread: TPS62140

Hello,

During RTCA/DO-160E, Section 20 Radio Frequency Susceptibility, Radiated Susceptibility, the unit experienced failures between 230 and 400 MHz during the 0.1-1GHz CWSW 100V/m (category W)]. We isolated the failure to the TPS62140 circuit. 

In our application, Vin=13.5V Vout=3.3V Per Figure 7 in datasheet FSW=Low, L1=2.2uH, Cout=10uF, Cs=4.7nF, instead of Cin=10uF there is a pi filter 10uF, 2.2uH and 47uF which is connected to PVIN and EN pins. There is an additional filter stage 10uF, 100ohm, 0.1uF before the AVIN pin.

Question: Throughout datasheet recommendation is to tie AVIN and PVIN together. What are the differences between the AVIN and PVIN pins? With the RF voltage on 13.5V input, the voltage at PVIN pins may be different than the voltage at AVIN pin, what is the effect of this difference?

  • 0
    TI__Guru**** 151520 points

    It sounds like you are failing radiated.  Do you have any issues with conducted?  Are you ale to post (or send me in a private message) the radiated plot which fails?  What load is this taken at?

    The block diagram in the D/S (Figure 5) should show the difference between AVIN and PVIN.  PVIN is Power VIN and just goes to the power FETs.  AVIN is Analog VIN and goes to the control circuitry.  Splitting them is common on higher current devices to keep the PVIN noise out of AVIN.  This should not affect EMI.

    Could you post your PCB layout?