Need recommended / example values for TLE9278 SMPS Buck circuit without Boost

[SRA]

I'm looking for an example set of recommended values for inductor and capacitors on the input side of the SMPS when not using boost on the TLE9278 Multican SBCs.

https://www.infineon.com/dgdl/Infineon-TLE9278BQX-DataSheet-v01_50-EN.pdf?fileId=5546d462689a790c016...

Page 119, Section 14.1 listed a set of example parts that could be used. Unlike the other products in the DC/DC range, the TLE9278's example ONLY show examples with SMPS Boost. The difference is that the L1 / Inductor 1 / input to the Buck circuit is shown as 22-47uH, but that other parts when not using boost recommend a 2.2uH.

The size difference in a 22-47uH inductor is minimum 3mm x 3mm. As where a 2.2uH inductor goes to 0402 and 0603 sized packages. Likewise, recommendations on the capacitors would be helpful.

I suspect it could be closer to the 2.2uH that the other SBC SMPS buck circuits call for. But I'd like a little direction before testing.

[Vishnu_Nambrath]

Hello, 

TLE9278BQX Boost and Buck regulators are working independently. 
If you don't use the Boost, No changes are to be done to the Buck regulator design. 
If you don't use the Boost, Please provide a filter against EMC and diode for the negative pulse and reverse voltage protection. 

Coming to the capacitor case size, depends on several factors. A few examples are given below. 
This makes the capacitor package selection dependent on the application. 

1. Some customer designs need to meet the min pad to pad distance for anything connected between the battery and ground line. 

2. Some customer designs need protection on all devices directly connected on the battery line to the ground. 

3. The ambient temperature and self-heating requirements. The design with T_amb 70C and 140C will have differences. Worst case ESR has to be calculated at 70C for the first one and for the second at 140C.  This will also influence on the self heating of the capacitor. 

4. Special EMC requirements for the applications

Hope is it clear to you. 

If you have any further doubts, please let us know. 

Thank you 

Vishnu Nambrath

[SRA]

Vishnu, that helps, but I'm not entirely there yet.

>If you don't use the Boost, Please provide a filter against EMC and diode for the negative pulse and reverse voltage protection. 

Right, so in this case, the diode is easy, but EMC filtering... That -in some example I won't hold you to- might be something like ... diode, 15uF electrolytic, 100nF ceramic, 2.2uF inductor, 1 to 10uF buck input cap. Does that seem like an example of reasonable EMC filtering for buck input for an application where say only 300mA was being used on 5V and 3V rails combined?

Everything else makes sense.

[Vishnu_Nambrath · Accepted solution]

Hello, 

You can use the same filter without D2 and remove the connection to BSTD. 
Based on the measurements on the board, you can reduce or replace the L1 with a jumper. 
If you can remove the L1, then you can also try to remove the electrolytic cap C1. C2 can-sized based on your micro cut-off requirements. This acts as a buffer cap for the short power supply interruptions. 

Thank you 
Vishnu Nambrath