0
\$\begingroup\$

I am working on a Buck/Boost converter design which is based on Buck/Boost converter TPS63070RNMT. Below is the schematic design. All the selected components are as per the Section 9 of the datasheet. enter image description here

U6 is powered by either USB (5V) or a rechargeable battery (2.8V-4.2V) as shown in the Schematic below. Expected Output is +3.3V/2A. enter image description here

USB connection is given priority in the design. If both USB & battery are connected to the board, PCB will be powered on by USB while battery gets charged.

The issue I am facing upon powering up is U6 not working as expected. Output is approx 1.2V and there is a lot of humming sound coming out of inductor. U6 is getting heat up very quickly. It is also affecting Original input waveformsand other sections. For example, USB input = 5V DC is superimposed with square wave. VBATT net on U1 also has some distortion in the form of sawtooth signal.

I am suspecting the inductor saturation issue. Did anyone face similar issue earlier?

Below is the layout of 3.3V supply section. It is as per the recommended layout mentioned in datasheet.enter image description here Copper pouring added for VIN, Inductor nets and 3.3V. There is a 3.3V copper plane on Layer 3. On TOP layer, whole section is surrounded by Ground copper.

Need some inputs from the expert.

Thanks in advance.

\$\endgroup\$
4
  • \$\begingroup\$ did you take care of the saturation current rating of L3 \$\endgroup\$
    – Navaro
    Commented May 15, 2019 at 18:30
  • \$\begingroup\$ @Navaro Yeah. L3 rated saturation current is 14A which ia way higher than what datasheet recommends. In boost mode, for Iout=2A with minimum Vin=2.8V, Ipeak comes around 2.68A as per formulae mentioned in Page 18 of datasheet. . It is recommended to choose an inductor with a saturation current 20% higher than that value. \$\endgroup\$
    – Lalit
    Commented May 15, 2019 at 18:46
  • 2
    \$\begingroup\$ For switching supplies, board layout is important. Please don't keep it secret. \$\endgroup\$
    – CL.
    Commented May 15, 2019 at 19:17
  • \$\begingroup\$ @CL. I have added the layout picture. Have a look. \$\endgroup\$
    – Lalit
    Commented May 16, 2019 at 6:52

1 Answer 1

Reset to default
0
\$\begingroup\$

Found the issue and resolved it. GND pins of C14 and C15 must be connected directly to PGND pin of U6 (Pad between L1 & L2) on the top layer. It is important to make a good GND star connection, the inductor lines for L1 and L2 nets are not so critical, they can go to the inductor through vias and another layer.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.