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TPS65916: All LDOs are ok, but SMPS can't operate fuctionally

jianfeng tsai
Prodigy 30 points
Part Number: TPS65916

Dear all,

TPS65916 is used in my project and some difficult issues happen. An TPS65916EVM is used to check the original design (named as project-A).

In project-A, all LDOs can work well if none of the five smps are used (it means the SMPSX_SW are all disconnected).

The I2C GUI can read and write register. I think the PMIC works normally.

After SMPS5 are connected (inductor, input pin, feedback  pin are connected), the PMIC are down and GUI lose the I2C with the PMIC.

I check the SW pin of SMPS5 and the scope result is post here (the channel 2 ,blue line)

I guess that the PMIC do make SMPS5 to switch for 1ms (in 2.2MHz .. duty 50%) and stop for uncertain reason.

Hope that  someone familiar with this PMIC could give me some tips to solve this issue.

(Sorry for that I may not describe the problem well in English)

  • 0
    TI__Intellectual 950 points
    Hi,
    Your question has been forwarded to the responsibly engineer, thank you for choosing TI
  • 0
    TI__Genius 10000 points
    Jianfeng,

    Hi, thanks for using E2E. Can you re-attach the scope shot you had? I was not able to open it.

    Also, when you are saying that you are adding the SMPS5 connections, is that on the EVM or on your project-A board?

    I2C should work once VCCA, VIO, and VRTC are all high. Can you check these rails?

    Thanks,
    Nastasha
  • 0 in reply to Nastasha
    Prodigy 30 points

    Hi Nastasha,

    Without trying to use SMPS5,  I2C works ok and VBG LDO1 to LDO5 also work well in prohect-A board.

    I can use GUI (jumping I2C pins from EVM MSP430 to project-A pins) to read and write some registers or change GPIOs' function of project-A board.

    While trying to connect SMPS5, I am in trouble (for other SMPSx, it is also  problematic).

    Scope shot if re-attached in jpg format. Thanks for your help.

  • 0 in reply to jianfeng tsai
    TI__Genius 10000 points
    Jianfeng,

    Thanks for further explaining. Can you also tell me what is the load on SMPS5? Also, what is the full part number of the PMIC that you are using?

    If you can attach your schematic (PMIC portions only) that would be helpful in understanding how you have the PMIC setup.

    Thanks,
    Nastasha
  • 0 in reply to Nastasha
    Prodigy 30 points

    Hi Nastasha,

    The full part number is TPS659162RGZR.

    The load on SMPS5 is quite small (below 50mA) since I have used EVM's SMPS5 to drive the load without any issues.

    The original schematic is as follows,

    First, project-A is re-worked (modified-1) as below and it works as the description in fig.

    Then, project-A is re-worked (modified-2) as below and it works as the description in fig.

    Finally, project-A is re-worked (modified-3, disconnect all pins of SMPSx) as below and it works as the description in fig.

    From above, I think some confusion is:

    1. If no SMPSx is used, how to setup these pins correctly to make LDOs and I2C works normally.

    2. If only one SMPS is used, how to setup other pins and make LDOs and I2C works normally.

    3. The scope shot is take in (modify-2). What's mechanism to stop switching and restart switching periodically .

    Thanks again to help me clarify this design. Thank you!

  • 0 in reply to jianfeng tsai
    TI__Genius 10000 points
    Jianfeng,

    Have you seen our schematic of the EVM in our user guide? www.ti.com/.../sliu021.pdf
    Additionally, the datasheet tells you what to do with a pin that is not used in section 3.1.

    in general, here are the important factors:
    1. All SMPSx_IN pins need input caps (4.7uF) placed close to the pin and should be pulled up to the same voltage as VCCA.
    2. All LDOx_IN pins need input capas (2.2uF) placed close to the pin and should be pulled up to the same voltage as VCCA.
    3. LDOx_OUT pins being used need an output capacitor (2.2uf), they can be left floating if unused.
    4. SMPSx_OUT pins being used need 1uH inductor and a 47uF output cap, they can be left floating if unused.
    5. VCCA needs a 10uF cap placed near the pin.

    Also, GPIO5 can be used to turn on the device (with a high signal) or PWRON can work if you have a press button.

    What are you trying to do with the AND gates?
    Are your input caps next to the input pins?
    Please verify if VIO, VRTC, VCCA, and RESET_OUT are all at the correct voltage.

    Thanks,
    Nastasha