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TPS566242: Large output ripple/noise with or without load

Part Number: TPS566242

We have a design with TPS566242 that regulates 12V to 3.3V. However, we measured large output ripple/noise at TP6 either with or without load. We also measured the 12V input alone, and the input is clean. The ripple Vpp is up to 1.26V, and the noise is 2-100 MHz. How can we reduce ripple to within 100mV and noise?

Schematic

12V input

3.3V output, no load

  • Hi Jeff,

    Thanks for reaching to us!

    Some comments on your schematic:

    1. The Cout you used is quite large. Please change Cout according to datasheet recommended LC range. Then test Vout ripple to check whether issue still happens.

    2. The EN voltage you set is ~7.2V, beyond EN-pin absolute voltage 6V, so EN-pin has damage risks. Please correct it.

    Let me know your further test progress.

  • Hello Miranda,

    Thanks for your review. I removed 3 of the 220uF capacitors and only left one 220uF on the board. The ripple still exists:

    I'm trying to correct the EN pin voltage. Any further suggestions are welcomed. Thanks.

  • Hi Jeff,

    1. Please cut the loading trace to avoid loading effects. Did this issue only occur at light load? Could you change the loading current (use external load) and figure out a clear issue condition?

    2. Please use 20MHz bandwidth scope setting to eliminate high-frequency noises (measurement error), also use ground spring method to measure Vout waveform across output cap.

    3. Please measure SW & IL as well and share with us.

  • Hello Miranda,

    I changed EN pin voltage to 2.15V (with one 220uF). This is the output graph with no load (load is not connected). Previously the ripple happens either with load or no load. Is it possible the previous high EN pin voltage damaged the IC?

    For #2, I set to 20M bandwidth limit. Sorry I don't have a ground spring probe, but I also used this probe to measure another TPS model's output voltage on the board, and that output is clean. Here's the SW graph:

    About the input voltage, the noise is sent back to the DC input. The 12V input alone does not have noise.

  • Hi Jeff,

    The second SW waveform looks normal, while the first and third Vout waveforms are quite abnormal.

    Please solder a new IC on the issue board, let's firstly confirm whether the IC damaged or not.

  • Hello Miranda,

    Thanks for your suggestion. I think I have another board that's never powered on or connected to 12V. I'll fix the EN pin resistor on that board and get back to you later. If that does not work, I'll try to replace the IC.

  • Hello Miranda,

    I tested on another board with no load. I find that the ripple rarely shows when 20MHz bandwidth limit is enabled.

    No bandwidth limit:

    20MHz bandwidth limit and single trigger mode: sometimes there is larger Vpp

  • Hi Jeff,

    Thanks for your updates. So this issue looks like the measurement error. Generally we will use 20Mhz BW scope when measuring Vout ripple to avoid high-frequency measurement noises.

    Let me know if you have further questions. Otherwise I will close this thread.

  • Hello Miranda,

    Thanks for your help. I measured more with 20Mhz BW. How can I reduce this 800mV Vpp ripple that happens at least once per second?

  • Hi Jeff,

    Per we talked firstly, please use ground spring method to measure Vout waveform across output cap.

  • Hello Miranda,

    Thanks for your help. This is the measurement with the ground spring method on the output cap:

    I also used the ground spring method to measure another TPS model's output cap, and that one has no obvious noise.

  • Hi Jeff,

    Thanks for your updates.

    1. The IC is the new one, right? You've confirmed the IC didn't damage due to EN overvoltage, haven't you?

    2. What's the loading condition? Could you change output current (0A/0.1A/1A) to check the Vout and SW waveforms?

    3. You may send me the layout file, I would review your layout design.