TPS61021A: TPS61021A Large Ripple on the Output

Luke Paul51

Part Number: TPS61021A

Hello,

I have just started doing some verification testing on a new board design, which uses the TPS61021A as a supply to a cellular module. I am seeing really large ripple on the 4V output under no load (215 mVpp at 14Hz) and even larger ripple with a 2Ω load (1.9V @ 300kHz). When transmitting, the peak load is about 1.9A at 4V but that is with the cell module in TX mode. Input is a 3.6V battery. I am hoping to get the help of an FAE to look through the design with me. I wasn't a part of this design, and when I went through the TI Web Bench tool to check the design, it seemed to be off by quite a bit.

Thanks

over 4 years ago

0 Brigitte over 4 years ago

TI__Guru 58215 points

Hello Luke,

You can either post your design here or if you do not want to share it public, please send it to bcs_request_sh@list.ti.com.

0 Jasper Li over 4 years ago

TI__Mastermind 46905 points

Hi Luke,

please share the schematic, BOM and layout image of the tps61021A boost circuit. also the waveform you observed. we need the circuit of TPS61021A portion, which should be not confidential.

0 Helen chen over 4 years ago

TI__Mastermind 40080 points

Hi Luck,

The circuit is unstable. Please post you schematic and pcb of the TPS61021 part.

TPS61021 should be OK for this 3.6Vin/4V/1.9A application. Therefore, we need to check what is the wrong with your schematic and pcb layout.

0 Luke Paul51 over 4 years ago in reply to Helen chen

Prodigy 185 points

Hi Helen Chen,

Sorry for the late response. I never got the email notification that someone responded. Here is the schematic along with the layout. Let me know if you have any questions.

Thanks,

Luke

0 Luke Paul51 over 4 years ago in reply to Luke Paul51

Prodigy 185 points

I forgot to post images of the waveforms I captured. Here they are:

4V output no load (DC and AC measurement)

4V output constant 2Ω load

0 Helen chen over 4 years ago in reply to Luke Paul51

TI__Mastermind 40080 points

Dear Sir,

What is the ESR of C51, could you please post its datasheet for us to check?

You can reduce the output ripple by paralleling a 10uF/10V ceramic cap with C55.

0 Luke Paul51 over 4 years ago in reply to Helen chen

Prodigy 185 points

Hello,

This is the datasheet for the capacitor (PN: UWX1E220MCL1GB). It doesn't look like it specifies the ESR of the cap. I suppose I could do a DC test and measure/calculate its ESR.

e-uwx-1513414.pdf

0 Helen chen over 4 years ago in reply to Luke Paul51

TI__Mastermind 40080 points

Dear Sir,

I didn't found the ESR also. You can add some low ESR ceramic caps at the output side to check whether it could be helpful. The new added ceramic should be as close to the IC as possible.

0 Luke Paul51 over 4 years ago in reply to Helen chen

Prodigy 185 points

I have some caps coming soon. When I try them, I will let you know the result.

Thanks,

Luke

0 Helen chen over 4 years ago in reply to Luke Paul51

TI__Mastermind 40080 points

Waiting for the result. Good Luck!

0 Luke Paul51 over 4 years ago in reply to Helen chen

Prodigy 185 points

Hi Helen,

That certainly helped! Thanks for that idea. I was able to decrease my ripple at 2A to just over 300mV which is acceptable for my application. I used a 10uF Low ESR cap on the output like you suggested.

Thanks,

Luke

0 Helen chen over 4 years ago in reply to Luke Paul51

TI__Mastermind 40080 points

That's great, good luck!

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TPS61021A: TPS61021A Large Ripple on the Output