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TPS61178: 50% Efficiency and 20 kHz noise on output

Nick Bianchi
Prodigy 20 points
Part Number: TPS61178

Hi,

I am seeing only 50% efficiency with an input voltage of 12V, output of 16V, and output current of 1.5A. Also, I found there is a 20kHz noise that is coupled to the output, and can even be audibly heard when close to the IC. Are the issues caused by the supplementary passives I have chosen?

The following are the chosen supplementary passives:

L = 4.7uH

Rfreq = 887kOhms

Rlimit = 56.2kOhms

Rcomp = 133kOhms

Ccomp = 470pF

Rup = 1MOhm

Rdown = 80.6kOhm

Cbst = 1uF

Cvcc = 4.7uF

Thanks.

  • 0
    TI__Mastermind 21565 points

    Hi Nick:

    May you share the layout, and the waveform of Vin, Vout, SW pins for me? And what't the value of Cout, what's the current capability of the inductance?

    Besides, may I know the purpose you choose Rfreq = 887kOhms? The current ripple will be large with L=4.7uH, 200Khz.  

  • 0 in reply to Minqiu Xie
    Prodigy 20 points

    Hi Minqiu,

    I am unable to get the waveforms at this time. The value of Cout is approximately 80uF. The current rating of the inductor is 15A with its saturation current being 30A. I have attached a picture of the boost converter portion of the board layout. It is a 4 layer board and the only connection that isn't on the top layer is the a trace connecting Vout to Rup of the feedback network; this connection is shown in blue.

  • 0 in reply to Nick Bianchi
    TI__Mastermind 21565 points

    Hi Nick:

    As no waveform in hand, it's a little difficult to analysis. But I'll suspect the loop is not stable. 

    May I know if you have observed the waveform before? What's the ripple of Vout? Is the Vin stable?

    What's the load details? Is it constant or will it change during the operation?

    And how about try Rcomp = 15kOhms  Ccomp = 6800pF?