• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 62 subscribers
  • Views 635 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2121EVM-023: TPS2121 - Output power drop to 0V

Trong Duong
Prodigy 100 points
Part Number: TPS2121EVM-023
Other Parts Discussed in Thread: TPS2121, , LM5116, TPS61230

Hi TI team, 

I choose TPS2121 as a power switch for my Supercap Power Backup solution. Then, I buy one set TPS2121EVM-023 for testing before releasing the schematic.

On TPS2121EVM-023, I use XCOMP mode with configuration as below:

  • IN1 (Priority): +5V_REG (main power)
  • PR1: 2.475V
  • IN2: +5V_BOOST (backup power)
  • CP2: 2.273V
  • OV1=OV2=6.084V
  • Css = 1uF
  • ILIM = 4.645A (R21 = 21.5k)
  • Cout = 200uF

 

Case 1: No Load

When I unplug the main power supply, Output power (+5V_SYS) normally switch to IN2, but the switching time is 390ms. Is it normal?

 

Case 2: Load 1.2A

Switch from IN1 to IN2 is fine

Problem happen when I plug back Main Power, I detect a drop to 0V on my Output Power which maybe reset my device.

Please show me which I did wrong on my testing and help me to fix this dropout phenomenom.

I am looking forward to hearing from you as soon as possible

Trong.

  • 0
    TI__Mastermind 32650 points

    Hi Trong,

    Can you please describe in detail how you have setup the EVM? There are a lot of jumpers which change the properties of the device. 

    I would suggest drawing circles around the selected pins (jumpers) on the provided schematic (from the user guide) and posting a picture.

    I also have access to an EVM so I can run this use case in the lab with two 5V sources. What is your load? I would recommend using a resistive load instead of a electronic load.

  • 0 in reply to Shreyas Dmello
    Prodigy 100 points

    Hi Shreyas Dmello,

    Thanks for your reply soon.

    Below picture is my present setup on the EVM, please take a look.

    Besides, on the EVM, I have reworked on 3 positions for matching with my schematic:

    1. R10: Change from 10.2k to 12k

    2. R17: Change from 5k to 10k

    => V_CP2 = 5*10/(10+12) = 2.272V

    3. R15: Change from 5k to 10k

    => V_PR1 = 5*10/(10+10.2) = 2.475V

    As theoretical calculation, when IN1 (main power) drops down to 4.589V, TPS2121 will switch to IN2 (backup power)

    I test my setup with the load 500mA on the EVM, TPS2121 works well but the output voltage drop to 4V not approximately 4.5V

    Then, I test with the load 1.2A (simulated by 4 Ohm power resistor), and the dropout-to-0V phenomenon happen.

    Please feel free to discuss about my issue.

    Trong

  • 0 in reply to Trong Duong
    TI__Mastermind 32650 points

    Hi Trong,

    In your scope captures, what is the green waveform? By the way, your calculations are correct and the setup of the board matches the use case you describe correctly.

    I also notice that your supply voltages are not very strong. Could you please run this testing with stable supplies?

    I also noticed that you're dropout is occurring when IN1 comes up. When an input goes from invalid to valid, fast switchover is not possible. 

    The device will pass a deglitch time known as input settling time. If fast switchover is triggered before the settling time is complete, then the inputs will not switch and the device defaults into VCOMP mode followed by soft sart. Fast switchover is meant for situations where both supplies are available and valid. I think this is the cause of the output dropout. Input settling time and soft start are directly proportional to the SS cap used.

    The workaround to this is adding a delay on PR1 with a voltage relay to let input settling time complete and then trigger switchover. https://e2e.ti.com/support/power-management/f/196/p/827475/3061350?tisearch=e2e-sitesearch&keymatch=tps2121%25252525252525252520fast%25252525252525252520switchover#3061350

  • 0 in reply to Shreyas Dmello
    Prodigy 100 points

    Hi Shreyas,

    Thank you very much for your support. I followed your suggestion by changing from adaptors to another strong inputs. Immediately, XCOMP Mode works well.

    After that, I was busy with my Backup System using TPS2121 (XCOMP mode) to prepare for our new design. Then, I was facing with another issue. Let me show you this malfunction.

    • Main Power: 5V/6A (Supplied from LM5116)
    • Backup Power: Supercap -> TPS61230 (for Backup Voltage is kept at 5V until voltage of Supercap reaches 2.4V)

    I test with 5V/1.5A Constant Current Load and this malfunction happens:

    • Channel 1 (Yellow): Main Power
    • Channel 2 (Pink): Backup Power
    • Channel 4 (Green): Output of TPS2121

    Zoom In:

    There is ringing on Backup Power and the output of TPS2121 is unstable. These things make my system reset every time I unplug Main Power.

    As you mentioned about strong input, then I test the TPS61230 and see that it has bad Load Transient Response at 1.5A Load:

    TPS61230 - No Load to Heavy Load

    TPS61230 - Heavy Load to No Load

    As I use XCOMP Mode, output of TPS61230 will supply for CP2 through resistor divider circuit, so V_CP2 = 2.272V (TPS61230 - No Load). When Main Power falls down to approximately 4.5V (V_PR1 = 2.272V), TPS2121 switches to Backup Power, TPS61230 now changes from No Load to Full Load and a drop 450mV happens known as Load Transient Response. This time, I think TPS2121 does comparison again and fall into malfunction.

    I wonder if my explanation is the reason lead to this ringing phenomenon of XCOMP mode? If so, how can I solve the issue without changing any parts?

    I tested with XREF Mode, it works so well. Unfortunately, I formed my design using XCOMP Mode, so if it is the only way - change from XCOMP to XREF, I must do some reworks.

    Please kindly discuss with my about my issue.

    Trong

  • 0 in reply to Shreyas Dmello
    Prodigy 100 points

    Hi Shreyas,

    Thank you very much for your support. I followed your suggestion by changing from adaptors to another strong inputs. Immediately, XCOMP Mode works well.

    After that, I was busy with my Backup System using TPS2121 (XCOMP mode) to prepare for our new design. Then, I was facing with another issue. Let me show you this malfunction.

    • Main Power: 5V/6A (Supplied from LM5116)
    • Backup Power: Supercap -> TPS61230 (for Backup Voltage is kept at 5V until voltage of Supercap reaches 2.4V)

    I test with 5V/1.5A Constant Current Load and this malfunction happens:

    • Channel 1 (Yellow): Main Power
    • Channel 2 (Pink): Backup Power
    • Channel 4 (Green): Output of TPS2121

    Zoom In:

    There is ringing on Backup Power and the output of TPS2121 is unstable. These things make my system reset every time I unplug Main Power.

    As you mentioned about strong input, then I test the TPS61230 and see that it has bad Load Transient Response at 1.5A Load:

    TPS61230 - No Load to Heavy Load

    TPS61230 - Heavy Load to No Load

    As I use XCOMP Mode, output of TPS61230 will supply for CP2 through resistor divider circuit, so V_CP2 = 2.272V (TPS61230 - No Load). When Main Power falls down to approximately 4.5V (V_PR1 = 2.272V), TPS2121 switches to Backup Power, TPS61230 now changes from No Load to Full Load and a drop 450mV happens known as Load Transient Response. This time, I think TPS2121 does comparison again and fall into malfunction.

    I wonder if my explanation is the reason lead to this ringing phenomenon of XCOMP mode? If so, how can I solve the issue without changing any parts?

    I tested with XREF Mode, it works so well. Unfortunately, I formed my design using XCOMP Mode, so if it is the only way - change from XCOMP to XREF, I must do some reworks.

    Please kindly discuss with my about my issue.

    Trong

  • 0 in reply to Trong Duong
    TI__Mastermind 32650 points

    Hi Trong,

    Good to see that your design is moving forward.

    I think your understanding of the situation is correct. Because of the ringing on the second input, the output is being affected. This happens because of the sudden loading on the boost during a fast switchover.

    What is your total input capacitance on IN2? I think you may be able to add  more capacitance to smooth out the waveform. 

    Please retry this fast switching in the XCOMP mode with the boost on IN2.