TPS63031: Power management forum

Russell Kean

Part Number: TPS63031

Hi,

We recently had manufactured 10 PCBAs from a professional manufacturer which includes a TPS63031 to regulate the voltage from a 4000mA LiPo battery to 3.3v. The schematic and PCB layout are as per TI datasheet (see attached file)

This was not a new run of these boards; we have previously had 20 PCBAs made by the same manufacturer without any problem. This time all the circuits exhibit the same or similar behaviour.

The first time a board is powered up from an external bench supply (lead length 10cm), Vout from the TPS63031 rises to around 0.4v. If the power is cycled, the second time the board is powered up Vout hits 3.3v. In some boards Vout remains at 3.3v for however the bench supply is on, in others it remains at 3.3v for 2 to 3 seconds before dropping back to 0.4v.

Replacing the external bench supply with a 3.7v 4000mA LiPo, Vout remains at 0.4v

Any thoughts?

Regards

RussellTPS63031 schematic.docx

over 5 years ago

0 Milos over 5 years ago

TI__Expert 7925 points

Hi Russel,

Thanks for reaching out. Could you please answer the following questions:

Is the second batch of boards identical as the first one (layout, schematic and parts)?
Could you please send us the PCB layout (just a snippet around the TPS63031 is enough, ideally showing all the layers in separate images).
Could you please send us the scope plots (showing Vin and Vout) during incorrect startup, and if you can also catch the drop back to 0.4 V.
What is the load and is it present during startup?
The failing units (especially those that drop back to 0.4) - can you see anything else, for example are they getting too hot?

Some things that you could try in the meantime:

Inspect the solder joints, especially the thermal pad.
A-B-A swap: Swap the ICs between the working and the failing board, and then check both boards to see if the problem still exists.

Thanks and regards,
Milos

0 Russell Kean over 5 years ago in reply to Milos

Prodigy 30 points

Thanks for your prompt reply Milos.

Answer to your questions.

1. Yes, except for an added pull up in a completely different part of the circuit

2. PCB layout attached.

3. Will forward these if/when I can capture them

4. There is a thermal fuse, an FERMTOSMDC020F-2, with a hold current and trip current of 200mA and 450mA respectively, at the input of the TPS63031. the output of the TPS63031 feeds a SAM21D micro, SD card, I2C temp sensor and a magnetic encoder. In the previous boards, this set up worked perfectly. With all the new boards, the output voltage on the TPS63031 side of the fuse motorboats between 1 and 2 volts at several hundred hertz. Removing the fuse, the output of the TPS63031 functions at described above - Vout =0.4v on the first power up. Powering the unit off, and immediately powering it back up again, Vout = 3.3v on all boards.

The output will stay at 3.3v in some of the boards as long as the external bench supply is on, or drop back to 0.4v in others after second or two. In those boards that remain powered, it appears that the initial current is 100mA before dropping back to 21mA once the micro has booted.

This would suggest that an inrush current is impacting on the operation of the TPS63031. Could this behaviour be explained by a poor thermal pad connection?connection? The solder joints on the pins appear to be ok.

5. On those boards where Vout remains at 3.3v the temperature is at ambient (21dec)

0 Milos over 5 years ago in reply to Russell Kean

TI__Expert 7925 points

Hi Russell,

Sorry, I overlooked your response. You must've accidentally marked the thread as resolved, however the issue still exists, right?

Yes, this looks like an inrush current induced problem, and the device is stuck in UVLO oscillations caused by high input resistance. This could happen if the battery ESR or series resistance (cables, fuses, load switches...) is too high, or if the power ground (thermal pad) is not properly soldered. Please check if the thermal pad is properly soldered. We had a few cases where the solder mask was not removed under the thermal pad.

To solve this, I suggest again:

Please make the scope plots showing VIN and VOUT voltages during the startup. Please do this measurement also for the functioning boards. It might happen that they also oscillate, but they start-up after some time.
There is no PCB layout in the attached docx file, could you please reupload it again?
Please try A-B-A swap: exchange the device on one functioning and one failing unit and cross check the functionality.

Best regards,
Milos

0 Russell Kean over 5 years ago in reply to Russell Kean

Prodigy 30 points

Thanks Milos.

Please find attached the PCB layout which I neglected to attach last time. There's a via beneath the thermal pad. Possible that during the flow soldering process that solder wicked into the via and away from the thermal pad?

Regards

Russell

8078.TI.docx

Regards

Russell

0 Brigitte over 5 years ago in reply to Russell Kean

TI__Guru 65170 points

Hello Russell,

Thank you very much for the layout. When I downloaded the schematic, it seemed to be corrupted. Would you please check it?

Is the GND via new to the second batch? It is possible that the solder get away from the pad if the via is big enough for it to pass. Please ask your manufacturer.

Please check for all other differences, even very tiny ones.

Please try to take the measurements described above to get a better understanding of the issue.

Can you try if slowing down the startup or increasing the startup speed causes a change in the issue? Does a change in the input voltage change the behavior?