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TPS61120 Ripple on Boost Output

bd5077
Intellectual 270 points
Other Parts Discussed in Thread: TPS61120

This is the ripple that I am seeing on the Vout of the TPS61120


Vin = 5.0V

Vout = 5.5V

C6 = 2.2uF mono

C4 = 100uF tant

L1 = 10uH

Why is this low frequency ripple there?

  • 0
    TI__Intellectual 1305 points

    Hi Bruce,

    Could you please also share the load condition and schematic?

    Besides, I'm also curious about the first waveform, where the output voltage only changes from 1.17V to 1.88V. So the converter didn't boost to 5.5V as you expected?

    BR

    Gene

  • 0 in reply to Gene Lu
    Intellectual 270 points

    The waveforms are AC coupled and expanded to see the ripple.

    Is this ripple or ringing?

    It is not at the switching frequency.


    Load is about 120mA

  • 0 in reply to bd5077
    TI__Intellectual 1305 points
    Hi Bruce,
    It seems that the converter works in Power save mode so its frequency is low, but with very large output ripple (about 700mV). I need more information to find why it has such a large ripple. Please help me to find out:
    1) What's the actually voltage value of Cursor 1 and Cursor 2 in the first waveform?
    2) Is the load dragging constant 120mA from Boost?
    3) Make sure the tantalum cap doesn't have large ESR.
    4) Adding more load at output and make it works in PWM mode to see if the ripple is still very large. Or connect the SKIPEN pin to ground to see the output ripple.

    BR
    Gene
  • 0 in reply to bd5077
    Intellectual 270 points
    The 100uF is indeed a high ESR (2ohm) device.
    I will replace it with a TPSC107M010R0075 (0.075 ohm)
    The ripple is not causing any noticeable problem but I can concerned with reducing radiated and conducted EMI