TPS62130: Implementation of TI reference design does not work with 4.73V input to create a 4V output. Everything checks out but still doesn't work

Paul Parkinson

Part Number: TPS62130

I have an implementation of the TI reference design for a 5V input to step down to 4V with the TPS62130. TI support says it matches the reference design and the layout follows (duplicates) the suggested layout. However, the design does not work. It did work the first time it was powered up with board 1 so the modem module was added (which is the load) and the board did not have power. A second board without the modem was tested and the power conversion circuit did not work upon the first or subsequence power cycles. Both boards display the same characteristics. FB voltage i 0.5-0.6V, Vout is .25-.27V. The input voltage is 4.73. There is a voltage on the SS/TR pin.

At the suggestion of TI Support, I changed to a higher input voltage. I applied 15V input and the Vout increased to 0.6V but not the expected 4V. Sadly I did not bring out the PG signal as the design was space-constrained and there was no use for the PG signal. Other than debugging so lesson learnt.

Any suggestions would be appreciated.

over 3 years ago

0 Emily Kong1 over 3 years ago

TI__Expert 3350 points

Hi Paul,

Would you be able to provide the schematic and layout details along with waveforms of the FB, Vin, Vout, and SW?

Best,

Emily

0 Paul Parkinson over 3 years ago in reply to Emily Kong1

Prodigy 80 points

Here is the schematic. Right now only the 5V USB or the MB-5VCC is used to power the circuit. I have no waveforms yet.

0 Paul Parkinson over 3 years ago in reply to Paul Parkinson

Prodigy 80 points

I am curious if anyone has experience with this part under no-load conditions? Can this part lock up under no load?

Thanks

Paul

0 Vincent Zhang(BSR) over 3 years ago in reply to Paul Parkinson

TI__Expert 4795 points

Hi Paul Parkinson,

Your schematic didn't upload successfully. Could you upload again? Thanks.

0 Paul Parkinson over 3 years ago in reply to Vincent Zhang(BSR)

Prodigy 80 points

0 Amod Vaze over 3 years ago in reply to Paul Parkinson

TI__Mastermind 24850 points

Hi Paul,

The soft-start cap (C4 470pF) looks really small so it is possible the device is hitting current limit during startup. During startup below 0.5V or so, the internal current limit is reduced to just 1.6A. So, with a smaller C4, and any additional load capacitance and load current, the device could be running into current limit and then the output voltage can foldback to a lower value as the current limit dominates over the voltage regulation loop. Can you try changing to 3.3nF or so and see if that helps the IC regulate? You can capture inductor current, SW, VOUT waveforms during startup to see what is actually happening as well. If possible, please also share the reference design link on ti.com. Hope this helps.

Thanks,

Amod

0 Paul Parkinson over 3 years ago in reply to Amod Vaze

Prodigy 80 points

The 470pF cap is the suggested size from the WEBENCH application. The design does not work in a no-load situation so I do not expect that there is a current limit issue.

I have attached the WeBench schematic.

Thanks

Paul

0 Emily Kong1 over 3 years ago in reply to Paul Parkinson

TI__Expert 3350 points

Hi Paul,

WEBENCH application suggestion aside, 470pF is a small cap to have on the SS/TR pin. Even in a no load condition, this can cause startup issues. Can you provide clear inductor current, SW, and Vout startup waveforms so we can have a better understanding of something occurring beyond this cap?

0 Paul Parkinson over 3 years ago in reply to Emily Kong1

Prodigy 80 points

I have been able to do more testing on the design. If the start-up load is greater than 1.509A the DC-Dc will not startup. At 1.508 and below it will startup. Are there any suggestions on how to improve the start up current capabilities?

If the 470pF is small is there a suggested size?

Thanks

Paul

0 Vincent Zhang(BSR) over 3 years ago in reply to Paul Parkinson

TI__Expert 4795 points

Hi Paul,

Are you testing on 44uF output capacitor or 22uF?

0 Paul Parkinson over 3 years ago in reply to Vincent Zhang(BSR)

Prodigy 80 points

I have tested with both 22uF and 44uF Capacitance. There was no change in the way the circuit functioned. It still fails to start if the load is over 1.5A.

Thanks

Paul

0 Paul Parkinson over 3 years ago in reply to Vincent Zhang(BSR)

Prodigy 80 points

I have tested with both 22uF and 44uF. The circuit acts the same with either amount of capacitance.

Thanks

Paul

0 Vincent Zhang(BSR) over 3 years ago in reply to Paul Parkinson

TI__Expert 4795 points

Hi Paul,

I suggest to send email to e-kong@ti.com for further debug. Thanks.

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TPS62130: Implementation of TI reference design does not work with 4.73V input to create a 4V output. Everything checks out but still doesn't work