Layout Guidance needed: Loop minimization by placing INN3679C beneath transformer
Hi,
We are facing a situation where there is a relatively large loop between the drain pin of the InnoSwitch-3-EP (INN3679C) and the transformer’s switch node. Since the transformer’s switch node is located at the center pin, it’s not possible to minimize this loop effectively with the current placement.
To address this, we are considering a double-sided component placement, where the IC would be placed on the bottom side directly underneath the transformer. This approach is also recommended in the datasheet.
However, our transformer is THT-mounted, and we would like to confirm whether placing the IC directly underneath it could cause any mechanical/thermal issues or any other issues?
When it’s acceptable to place the IC on the bottom side, what factors should we consider?
Can the components connected to the IC be placed close to the transformer pins?
Are there any creepage or clearance requirements that we need to maintain in this case?
Could you please advise if this approach is acceptable? This is an urgent topic, as we need to finalize the design for manufacturing.
Thanks a lot for your support.
Hi Manjesh,
Good day. Thank you for reaching out. Below are some recommendations and clarifications regarding your layout inquiries:
1) As you’ve mentioned, placing the IC directly underneath the transformer on the bottom side is a recommended approach, especially for minimizing the loop area between the DRAIN pin and the transformer’s switch node. This layout is commonly used in our reference designs and does not pose mechanical or thermal issues even having a through-hole transformer on the top side and the IC and other SMD components on the bottom side of the board.
2)There are no major restrictions if you want to place the IC on the bottom side, but a few things to keep in mind.
- Ensure that the transformer leads do not obstruct against the IC.
- Prevent routing traces beneath the IC.
- Maximize and enlarge the copper heatsink area of the SOURCE pin on the InnoSwitch3 device for effective heat dissipation.
3) Yes, placing components connected to the IC close to the transformer pins is advisable. This actually helps minimize parasitic inductance and improves overall performance by reducing loop area and noise susceptibility.
4) If you are asking for the creepage or clearance requirements between the transformer and pins and the IC, just ensure the safety spacing of the primary and secondary components. Please see attached image for the sample layout and design guide, components can be as close as possible to the transformer pins, as long as they don't overlap. Moreover, an important note you have to look into is the creepage and clearance distance, especially between high dv/dt nodes like the DRAIN pin. We usually follow the safety distance between the DRAIN pin and SOURCE pin as the minimum safety clearance throughout related traces and nearby components including the transformer pins.
You may also refer to a more detailed layout recommendations in our design guide for InnoSwithc3 Family. You can also visit our reference design found at the lower part of our website.
AN-72: an-72_innoswitch3_family_design_guide.pdf (power.com)
Thank you, kindly let us know if you have any further questions or clarifications.