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TPS63002: Ripples in Supply voltage

Yash Gupte
Prodigy 120 points
Part Number: TPS63002

have a TPS63002 IC and its circuit is designed for an input range of 3.5V-4.2V. The values of input and output capacitors as well as the inductor were calculated using WEBENCH. The circuit works exactly as intended, however, there is a peculiar problem. When observed on the Oscilloscope, the "Input" signal seems to have ripples whereas the "output" waveform is clean as a whistle. (Pic 1-6). The blue signal is the input signal while the yellow is the output. This behavior is consistent with load resistance values of (1k, 100, 50, 30, 20)(ohms).

The supply signal is smooth when the dc-dc converter circuit is removed and only the supply is viewed.

The design values are:

CIN=10uF

COUT=22uF

Ind=3.3uH ,112MOhm

Why does the supply have ripples in it?

Regards,

Yash Gupte

  • 0
    TI__Expert 8420 points
    Hi Yash,

    It looks to me like it is setup related.

    Could you add a big capacitor (in the 100uF range of higher ) at the input of the board and measure, this will act as a energy reservoir for you test setup.

    Could you share your circuit and layout too?
    What is the end application?

    Regards
    Sabrina
  • 0 in reply to Sabrina
    Prodigy 120 points

    I have attached the layout and an image of the PCB that was made.

    The application involves using a Lithium Ion battery and boosts its voltage to 5V to power an actuator with maximum current requirement of 300mA.

  • 0 in reply to Yash Gupte
    TI__Expert 5425 points
    I have never seen this device connected like that. This is not recommended, you can find an example of a recommended layout in the datasheet in section 11 starting on page 15.

    Critical parts for the layout are the connection of the input and the output capacitor. Those capacitors must be connected with low impedance connections. The input capacitor should be connected directly to VIN and PGND and the output capacitor to VOUT and PGND. Any excessive parasitic inductance in those connections will make the device performance worse.

    But this does not completely explain the ripple on the input voltage. Ripple voltages like that at the input can only be measured if you have a supply with a significant source impedance. On the PCB this can be narrow traces and input capacitors with significant series resistance (ESR). Sabrina already recommended to increase the input capacitance to address that.
    The wires and anything built in the supply connection like fuses or switches also contribute to the source impedance the converter will see at its input and finally of course the battery or the power supply used.

    I recommend to check all that and improve it if needed. If further debugging is needed I also recommend to measure the input current with a current probe in addition to the voltages you are already measuring.