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TPS63000: Trouble with the operation of a TPS63000 regulator

Part Number: TPS63000

Hi.

I'm having trouble with the operation of a TPS63000 regulator. The output is a 'sawtooth' waveform. See the attached picture.

This data is taken from the 10uF cap directly at the output of the TPS63000. You can see that they sawtooth form has a frequency of ~1.35 kHz, and voltage extremes at 1.52 VDC, and 3.78 VDC. The output should be 3.3 VDC.

The first thing I noticed is the low switching speed. The load on the regulator should only be a few dozen mA. VIN is ~4.7VDC. The PS/SYNC pin is pulled high, as is shown in the Typical Application Schematic The layout does not follow the guidelines exactly, unfortunately. The inductor is 2.2 uH and located directly next to its pins on the IC.

The output caps are directly at the output, however, the input capacitor is a few inches away from the VIN pins. Could this be the problem? Is it getting current-staved somehow?

Also, when I bypass this regulator and apply an external 3.3VDC to the board, things seem to work fine (controller boots, and runs, etc), and current draw is reasonable. So, this issue does appear to be an issue with the regulator.

I appreciate your help. If it would help, I can be reached on the phone at 310-408-0273

Thanks, Steve

  • Hi Steve,

    Can you share your schematic and layout for better check?

    What power supply are you using? If current limit was set too low, similar phenomenon could appear.

    The input capacitor is too far which is not recommended.

    Best Regards,

    Yichen Xu

  • See the attached images.

    As I mentioned, the input capacitor is located elsewhere in the schematic, and on the board (a few inches away). The inductor, L1, is 2.2uH. Also, resistor R3 is now 1.13 M. (the data sheet incorrectly recommends a 1M resistor for 3.3 V generation)

    In the layout image, directly above the IC is the inductor, and the two output caps are shown to the right. The voltage feedback divider is out of frame.

    I have used both a bench-top power supply, as well as the USB interface on the board.

  • Hi Steve,

    The input capacitor is so far so you need to check the waveform of VINA to see if there is spike.(not likely if C1 is not damaged).

    The datasheet says 'TI recommends to keep the value for this resistor in the range of 200 kΩ.' which means R4 should not exceed 200kΩ instead of exactly 200kΩ. Setting R3 as 1MΩ is recommended so the R4 should be 178kΩ. According to your layout, R3 and R4 is too far from TPS63000 and the trace connecting FB pin is long and thin so it is easy to introduce interrupt.

    Although you mentioned the load should be dozens of mA, it is necessary to check current waveform of inductor since you did not mention what load you used. Please disconnect real load and use only resistor or electronic load first, to make sure the device can work alone well. You need to remove inductor and place it vertically first, then using a jump wire to connect one side of inductor to the pad, while soldering another side of inductor right on the other pad. And you can measure the current through the jump wire. 

    Best Regards,

    Yichen Xu

  • Hi Stephen:

    As long time no hear from you, I assume you have solved the issue. If not, just reply below. Thank you!

  • Not yet. Going to try your recommendations tomorrow. Waiting for parts.