TPS 62150 Layout and noise

Silver Diamond

Other Parts Discussed in Thread: TPS62150

I am looking for layout feedback and other recommendations.

I asked for help for issues with the TPS62150 on http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/t/255949.aspx

Every one came back and told me that most likely it is board layout and provided a recommendation to reduce resistor values. I reduced the voltage divider resistances and the power supply works much better, but still adds noise as shown on below. First is without a load, second is with a load, supply about 150 mA of current. Notice the mean on the fist one is 5.08V as expected, and on the second one is 4.53 - much less then expected. Peak to peak is also rather high. I am working on layout which is also below. Is it probable that layout will fix the issues or will I need to play with filter caps? NOTE, my input is battery, and there is no noise on input line when power supply is not enabled.

YELLOW - INPUT
CYAN - OUTPUT

I reworked the board and would like some help. This is my first time designing Power Supplies using TI chip.

Front

Rear

over 12 years ago

0 Chris Glaser over 12 years ago

TI__Guru**** 150950 points

Thanks for posting your layout and scope shots. I'm glad the smaller FB resistors fixed things for you. It would be good to post your results on the old thread to close that one out.

The layout you posted is very good-almost exactly like the EVM's. Is this the one that gave you trouble?

If so, I think the problem may be in where you measure the output voltage. IR drops across traces take your regulated output voltage and lessen it as it travels across the board. You need to measure the output voltage where the IC senses it (before R7) to see the performance of the IC. Otherwise, you measure the performance of your PCB routing.

Measuring signals at a 20 nsec scale is very difficult. You need to use a low inductance probe as described in this app note: http://www.ti.com/lit/an/slva494a/slva494a.pdf

I doubt those signals are really present and causing issues for you.

0 Silver Diamond over 12 years ago in reply to Chris Glaser

Genius 4010 points

Chris,

I did not make the posted layout yet, I wanted some feedback before making it. Sounds like you agree with it, which gives me confidence to make it. These oscilloscope captures are for the old (bad) layout.

0 Chris Glaser over 12 years ago in reply to Silver Diamond

TI__Guru**** 150950 points

You can also order the EVM to get a known good layout. The gerbers for it are found on the EVM page also. You can download these and use them for your board as well.

0 Silver Diamond over 12 years ago in reply to Chris Glaser

Genius 4010 points

Yes, the issue was the layout. The new board output is pretty stable, works great. I used the following guidelines:

http://www.edn.com/design/components-and-packaging/4390811/PCB-layout-considerations-for-non-isolated-switching-power-supplies

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TPS 62150 Layout and noise