TPS62173: EMI issues

Hello Marco,

EMI reduction has a lot to do with layout. I recommend you read this very usefull App note: www.ti.com/.../snva638a.pdf

We also have training video that could guide you and help your design: training.ti.com/designing-wide-vin-low-emi-power-converters-any-application

If you have any other questions, please ask.

Thank you very much!

Best Regards,

Dorian

Hello Dorian,

Thank you for the App Note. I've read similar ones but the more the better.

According to the AN, I can apply a couple of improvements to my design. In particular, I'm planning to add a ground plane in the PCB inner layer close to the layer the regulator is mounted on. However, there's nothing blatantly wrong right now (ie. no big current loops) and I'm constrained by mechanic requirements.

So, I'm going to try to redesign the PCB but I'm also checking with you if the IC itself is something I should worry about. For instance, I've noticed that when it operates in Power Save mode there's some ringing when "releasing" the inductor, as visible in the datasheet scope screenshots. The AN also proposes to slow down the high-fet turn on time using a gate resistor or a resistor in series with the bootstrap capacitor, but those components are internal to the IC, so I can't try to do that.

My question was more like "Am I putting myself in the corner by using this specific switching regulator and should look at other TI parts or does it have average characteristics so there would be no particular benefit from choosing another part?".

Hello Marco,

To help you better, can you provide your input Voltage, Output Voltage, Load ? What are your main constraints? You said previously that you had mechanic requirements.
We may recommend you in that case another part.
Did you pick an inductor from the recommended list?

The origin of ringing on the SW pin is that Buck converters have a resonant circuit of inductance L and parasitic cap on high and low-side switches. This has negligible impact in CCM but in DCM a resonance can be observed, inductor current ringing will appear. These ringings can imply an increase of EMI as well as higher losses then a lower efficiency of the converter.

Thank you very much!

Best Regards,
Dorian

Hello Dorian,

Here are my params:
Vin = 11V-15V
Vout = 5V
Iout = 100mA

My constraints are essentially mechanical: the PCB is 25 x 35mm and it's quite dense. I don't have much space for the buck converter and I can't move it much further away from the external connections that seem to act as the antenna.

The inductor is a VLF302512MT, which comes from the recommended list in the datasheet.

Thank you