TPS54302EVM-716: Voltage Ripple Output is too big

Ramon Sidler

Part Number: TPS54302EVM-716
Other Parts Discussed in Thread: TPS54308EVM-876, TPS54308, TPS54302

Dear TI Team

On our PCBA's we use the TPS54308 Step-Down Converter for our 5V power supply. The PCBA and the Step-Down Converter itself gets powered by 24V. We expected an voltage ripple around 20mVpp. But on our PCBA we had voltage ripple around 100mVpp. We decided to order 2 evaluation boards. The TPS54308EVM-876 for 3.3V and the TPS54302EVM716 for 5V. We powered both of them with 24V and put an resistor on them to pull 300mA. The result on the TPS54308EVM-876 for 3.3V looked like the picture 7 in the datasheet. But on the TPS54302EVM716 for 5V we had a voltage ripple around 100mVpp. While we measured the voltage we checked the current constantly and recalibrated the oscilloscope before we measured. We havent changed anything on the evaluation board and measured in AC mode. Am i missing an information in the datasheet or is there something wrong with the mV/div. scale in the figure 22? The signal looks exactly the same, but the voltage is a lot bigger.

Thank you for answering and have a great week

Ramon Sidler

over 4 years ago

0 Shawn Nie over 4 years ago

TI__Genius 10070 points

Hi Ramon,

TPS54308 work in Force CCM at light load, the output ripple is small, but the efficiency is low.

TPS54302 works in Eco-mode at light load, the efficiency is high by decreasing the switching frequency, so the output ripple is large.

In Eco-mode, the output ripple is related to the output current, the switching frequency increases with the increasing of the output current, and the output ripple would be lower.

Shawn

0 Ramon Sidler over 4 years ago in reply to Shawn Nie

Prodigy 50 points

Hello Shawn,

Thank you for the fast answer. So as i said, we have the TPS54308 on our PCBA. If i understand everything correctly, the Step-Down Converter i have to use is the TPS54308, because we just pull 300mA at max. But in the picture below the text, you can see the voltage ripple of our PCBA. Can you tell me what we are doing wrong? The scematic is also down there.

Ramon

0 Shawn Nie over 4 years ago in reply to Ramon Sidler

TI__Genius 10070 points

Hi Ramon,

There is no issue for the schematic, could you please share the layout? Let's review it.

And it would be better to test the waveform (iL, SW, Vout).

What is the part number of the output capacitors?

Shawn

0 Ramon Sidler over 4 years ago in reply to Shawn Nie

Prodigy 50 points

Hi Shawn,

Before we review the layout i want to know, why our results on TPS54302-EVM716 dont look like the results on your datasheet. We did the measurement on the TPS54308EVM-876 aswell and got the results from the datasheet. But on the TPS54302-EVM716 with the same voltage, the same current. We got a voltage ripple twice the sice of your datasheet result.

Vcc was 24V.

Ramon