TPS5420 design review

mitch meiss

Other Parts Discussed in Thread: TPS5420, LM3480

Attached is my schematic. This is an automotive IoT device that will connect to the headers on a raspberry Pi. It will sniff the can bus on Semi Trucks and collect data from the internal controllers and send it via a cell modem to the cloud. Ultimately there will be analysis on this data that will be able to tell a fleet manager that truck 47 will break down due to ____ in 48 hours. The analytics is finished and there are 100's of working prototypes in the field. I am building version 2.0 for my client. I will be implementing a cell modem soon but this shouldn't be needed when looking at the buck converters.

Specifically I am using the TPS5420 to regulate 12V to 5V and the LM3480 to regulate 5V down to 3.3V.

If anyone spots any errors I would love to catch them now.

Thanks for all of the help!

SchematicReview.pdf

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

How did you choose the output filter components for TPS5420? What is the ESR of C5?

0 mitch meiss over 8 years ago in reply to JohnTucker

Prodigy 170 points

Sorry about that, the ESR is < 5 and the filter components were selected using the data sheet under the application circuits header

0 JohnTucker over 8 years ago in reply to mitch meiss

TI__Guru**** 191445 points

Less than 5 mohm...is that a ceramic?

0 mitch meiss over 8 years ago in reply to JohnTucker

Prodigy 170 points

So I used the exact cap from the data sheet. Its Tantalum AVX TPSD107M010R0080. For some reason I thought it was <5 but its actually 80mohm. I just double checked. I also sourced the footprint to make sure it was correct for that cap. Its technically a ceramic.

0 JohnTucker over 8 years ago in reply to mitch meiss

TI__Guru**** 191445 points

Should be good to go with that then.

0 mitch meiss over 8 years ago in reply to JohnTucker

Prodigy 170 points

Perfect, and everything else seems to look okay?

Appreciate it,

Mitch

0 JohnTucker over 8 years ago in reply to mitch meiss

TI__Guru**** 191445 points

I can't really comment on anything else. I only support TPS5420 (and many others not in your schematic).

0 mitch meiss over 8 years ago in reply to JohnTucker

Prodigy 170 points

No problem,

The last question I had is how can I select the inductor part number in order to handle the switching current?

0 JohnTucker over 8 years ago in reply to mitch meiss

TI__Guru**** 191445 points

What specifically is your question? There are in general two factors to consider, saturation current rating and heating (RMS) current rating. Usually I pick the saturation current to be equal to the current limit. For many modern inductors, the saturation is "soft" So you can be above the saturation rating and still have significant inductance. For RMS, it depends on your operating temp. How much increase in inductor temp can you tolerate? Usually I choose RMS > current limit also. Added benefit is higher current rating generally gives lower DCR and better efficiency.

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TPS5420 design review