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TPS61089: TPS61089 Output ripple problem

Kevin Chen
Intellectual 390 points
Part Number: TPS61089

Hi,

I use the TPS61089 in a boost circuit，Vin=5V, Vout=8.9V, Iout=2A. But the output ripple is 1.5V peak to peak.  I dont know what is the problem.

The circuit ：

The SW (yellow) + Inductor current (green):  Iout=2A

The Ouput Ripple (yellow) + Inductor current (green):  Iout=2A

The SW (yellow) + Inductor current (green):  Iout=1A

  • 0
    TI__Mastermind 40080 points

    Dear Sir,

    Change C53 to 471(47pF), then check it again.

  • 0 in reply to Helen chen
    Intellectual 390 points

    Hi Helen,

    The C53 is Not Connect in circuit .Then I change it to 471: 

    The SW (yellow) + Inductor current (green):  Iout=1A

    The Ouput Ripple (yellow) + Inductor current (green):  Iout=1A

    Change C53 to 100pf :

    The SW (yellow) + Inductor current (green):  Iout=1A

    The Ouput Ripple (yellow) + Inductor current (green):  Iout=1A

    The output ripple is still 1.3V peak to peak. Is it cause by the ESR of the output capacitors?

    Best Regards,

    Kevin

  • 0 in reply to Kevin Chen
    TI__Mastermind 40080 points

    Hi Kevin,

    The SW waveform looks normal after you let C53=100pF. But the current waveform looks strange. it should be a triangle wave instead of a sine wave.  What kind of probe you used in your application?  By the way, how did you test the output ripple, could u please send a picture to me? the test loop should be very very small, or noise will couple into the probe. What is the ESR of the 100uF cap. Suggest you parallel a 10uF ceramic with the current 0.1uF ceramic, this can help with the ripple voltage if it is caused by the big ESR.

  • 0 in reply to Helen chen
    Intellectual 390 points

    Hi Helen,

    I use the voltage probe with ground spring to test the output ripple. The test point is the two terminals of output capacitor.

    And I parallel two 10uF ceramics with the current 0.1uF ceramic as you say, the output ripple is down to 200mV peak to peak. So I think the problem is cause by the big ESR of 100u.

    Thanks for you help.

    Best Regards,

    Kevin

  • 0 in reply to Kevin Chen
    TI__Mastermind 40080 points

    Great， good luck!