TPS65220: PMIC Device failing to initiate power

Hi,

Thanks for reaching out. Here are a few observations on the schematic:

• TPS6522053 has the Bucks configured to operate in Quasi-fixed frequency and high bandwidth. This configuration requires a minimum of 30uF output capacitance (after de-rating). 47uF output capacitance per Buck is typically used. 

• If the AM64 RESETSTATz pin is driving the PMIC RESET pin, then the pull-up resistor is not needed. R33 should be uninstalled. The processor starter kit has an external pull-down resistor to keep the pin low during power-up and until the processor is out of reset. 

• Link to the TPS6522053 TRM which explains the PMIC default register settings: https://www.ti.com/lit/pdf/slvucj3

• Could you share a power-up scope capture with a ~4ms time scale showing the following signals:
  • VSYS
  • BUCK2
  • LDO3
  • BUCK3

Thanks,

Brenda

Hi Brenda,

Thanks for the response.

1. Is the capacitor requirement applicable to all the 3 buck converters?

In our case, we have provision for Buck1 - 31uF, Buck2 - 4uF, Buck3 - 19uF as of now. We can increase the Buck1 & Buck3 to 47uF+. But there is no provision for Buck2. Is that ok?

2. We checked the PMIC with RESET pin pulled low as well. There is no improvement in the situation.

3. We have gone through, and the configuration matches the requirements. 

4.  Please find the image (ch1- Vsys-3.3V, Ch2 - Buck2, Ch3- LDO3, Ch4-Buck3)

Please help us debug the issue further ASAP.

Thanks & Regartds,

Nanjunda M

Hi,

Yes, the same output capacitance requirement is applicable to the three Bucks. They all require a minimum of 30uF (after de-rating). 47uF is typical.

Could you isolate the PMIC from the processor and any load?

Thanks,

Brenda

Hi Brenda,

Thanks for the clarification. We will try with parallelling the capacitors for this.

We cannot isolate the PMIC from load since most of them are directly connected. 

Regards,

Nanjunda M

Hi,

We will keep this E2E on hold while you fix the output capacitance and collect the new waveform. 

I strongly recommend isolating the PMIC even it is requires uninstalling the processor and peripherals in one PCB. 

Thanks,

Brenda

Hi Brenda,

We added the capacitors to meet the 47uF output capacitance requirement for Buck converters.

But there is no change in the PMIC behavior. Please find the image (ch1- Vsys-3.3V, Ch2 - Buck2, Ch3- LDO3, Ch4-Buck3)

Meanwhile we are trying to assembly a PCB with independent PMIC IC & related supply. We will let you know once we have the assembled board.

Please let us know if anything else can be checked.

Thanks & regards,

Nanjunda M

Hi,

In the meantime, could you share the layout of the PMIC?

Thanks,

Brenda

Hi Brenda,

Please find the layout images.

Top:

GND1

SIg1

GND2

PWR1

PWR2

GND3

SIG2

GND4

Bottom

Please let me know if any clarifications.

Regards,

Nanjunda M

Could you share the PMIC layout file by private E2E message?

Hi Brenda,

We have 2 observations.

1. In the new board where we mounted only the power circuit and no load

- We checked the output without the capacitors (min 47uF)- output is 0 on all of the PMIC outputs

- After we added additional capacitors, we observed proper voltage outputs

2. In the old board, without isolating the load (processor and other components), we just increased the output capacitors on bucks to around 70uF.

But still, we did not see any output voltage.

Can you please let us know how to proceed further.

Thanks & Regards,

Nanjunda M

Hi Nanjunda,

We will review the information and provide an update within the next 24-48Hrs.

Thanks,

Brenda

Hi Brenda,

Any update on this?

Regards,

Nanjunda M

Hi Nanjunda,

Thanks for your patience. We are reviewing the layout and expecting to provide feedback within the next 24Hrs. 

Thanks,

Brenda

Hi Brenda,

Thanks for the review.

Is there any workaround for this?

Thanks & Regards,

Nanjunda M

Hi Nanjunda,

Layout errors typically require a new PCB revision. This will still be needed not only to fix the items highlighted in the previous message but also to add the 47uF output capacitance per Buck that was highlighted during the schematic review.

Nanjunda M1 said:

1. In the new board where we mounted only the power circuit and no load

- We checked the output without the capacitors (min 47uF)- output is 0 on all of the PMIC outputs

- After we added additional capacitors, we observed proper voltage outputs

What are the differences between the new and old boards? Based on this message, even with the non-optimized layout you are still able to power-up the PMIC with the correct voltages after adding the 47uF output caps are added. Am I understanding this correctly? If the issue happens after connecting the load/processor then I recommend having a full design review from the processor team so they can review the connections to the processor and peripherals. 

Thanks,

Brenda

Hi Brenda,

I understand we need to make new version of the PCB, but that takes some time.

W.r.t other board, which is working, we have not put any loads on the output. It is having only the input supply and TPS65220 and required circuits (inductors, caps, resistors). 

It does not contain the processor or any other related circuits on the board.

What could be the reason for this?

Regards,

Nanjunda M