TPS54202H / TMS320F28377D: Noise on power supply

Dyon Buitenkamp

Part Number: TMS320F28377D
Other Parts Discussed in Thread: TPS54202H

Hi,

I have created a PCB using the TMS320F28377D microcontroller. I have a buck switch regulator stepping down from >8V to 7V, then going to 3 different linear voltage regulators, where one of the outputs goes to the power circuit for the MCU. When I remove the connection between the regulator to the MCU power circuit, the power seems fine. But when I reestablish the connection and power on the MCU, there is suddenly a clear sinusoidal signal at 269kHz on the power lines. It affects everything, before and after the buck regulator as well as the linear regulators.

What might be causing this, and how should I go about fixing it? It affects the output of my op amp circuits on the board.

Thank you,

Dyon

over 3 years ago

0 tlee over 3 years ago

TI__Guru 62975 points

Dyon,

Am I correct in understanding that the buck regulator is not controlled by the F28377D MCU, and that the MCU is simply a load to the regulator? Further, the regulator works properly until you introduce changes in load (by connecting the MCU), at which point it becomes unstable?

If that is the case, I would recommend taking a closer look at the compensator design of the buck converter to make sure that the closed loop system is stable.

-Tommy

0 Dyon Buitenkamp over 3 years ago in reply to tlee

Prodigy 60 points

Tommy,

That is correct. Although, there are multiple regulators.

Here is part of the power circuit design:

I am not too familiar with buck converters. How would I check its stability?

- Dyon

0 tlee over 3 years ago in reply to Dyon Buitenkamp

TI__Guru 62975 points

Dyon,

I assume that you are having trouble with the integrated TPS54202H buck converter so I have moved this thread to the Power management forum for better support.

-Tommy