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TPS2121: Doubts with the configuration to work as a Power mux for Automatic Seamless Switchover with Priority (XREF) whitout an external precision regulator

ever quinones
Prodigy 30 points
Part Number: TPS2121

Hello.

I am currently working on the development of a device that fulfills a function similar to that of the UPS. The fact is that I have 2 12V power supply and I must have priority over one. I found the TPS2121 chip and it fits perfectly for what I should do. I have reviewed all the available documentation and I have little doubt regarding the configuration in XREF mode.

Since the space of my PCB is limited and thinking of not increasing the cost of BOOM I don't want to add an external 3.3v regulator. I have used the following configuration for my circuit, I place the image below.

I would like to know if the configuration that I have implemented is fine or can present failures when manufacturing the device. On your page I have not found the simulation tool of the TPS2121, I would like to know where I can find it available to perform the simulation.
Is it mandatory that you use an external regulator?
The main POWER SUPPLY is 12V and its minimum voltage in the worst case is 11V.
The secondary source has a voltage of 12V and comes from an AC / DC module which has a variation of + -3%.
In the worst case I have: VPR1 = 2.763V if VIN1 = 11V
VCP2 = 2.81V if VIN2 = 11.7V.

I appreciate any guidance you can give me. Thank you.

  • 0
    TI__Genius 13760 points

    Hi Ever,

    Thank you for reaching out to the E2E forum!

    The TPS2121 simulation tool can be found in the product folder under the Design and Development tab. I would recommend testing the part with the TPS2121 EVM before manufacturing to ensure the functionality.

    As far as the configuration goes the fast switchover can be achieved using the the XREF and XCOMP. The configuration you have is the XCOMP configuration. One thing I noticed is that you don't have anything connected to IN2 in the schematic. I'm assuming VIN2 will be connected to this IN2 pin. In this set up the output will be chosen by PR1 and CP2.

    • PR1 > CP2 : IN1 = Output
    • PR1 < CP2 : IN2 = Output

    One thing to be mindful about would be the size of the output capacitor. Increasing the capacitor does decrease the dip of the output voltage during switchover, but it will also increase the inrush current. Depending on the magnitude of the load current, the added inrush current could potentially cause the device to current limit and shut itself down.

    Let me know if you have any other questions.

    Regards,

    Andy Robles

  • 0 in reply to Andy Robles
    Prodigy 30 points

    Hello Andy.

    Thanks for your answer. 

    I just realized that I had no connection on the IN2 pin so this is a simple error, I have already solved it in my schematic.
    With regard to the configuration modes I have managed to understand them perfectly. According to the configuration that I have so that PR1 is greater than CP2 is there a difference of 0.1V, this would not be a problem? I am thinking of adding the integrated reference so that it gives me a reference voltage of 2.5v on CP2, in one of its evaluation boards the integrated one is powered by 3.3v, but I saw that 5V can be used, I would have no problem doing the VIN = 5V.
    The other point that I did not take into account is that of the condenser, it would be advisable to add 2 or 3 capacitors and that each one is 100uF?
    I await your reply.

  • 0 in reply to ever quinones
    TI__Genius 13760 points

    Hi Ever,

    With the variation range of your input voltages I see where the designed 0.1V difference could cause an undesired switchover.

    By the 5V reference do you mean you would input the 5V directly into CP2?

    The recommended operating range of PR1 and CP2 is 0V-5.5V. Applying 5V directly into CP2 is a possibility as long as the voltage divider to PR1 does not exceed 5.5V.

    For the output capacitor it doesn't matter if its 1 or more capacitors. The EVM was created with several output capacitors to give the users options to build different set ups.

    Regards,

    Andy Robles

  • 0 in reply to Andy Robles
    TI__Genius 13760 points

    Hi Ever,

    I haven't heard from you in few days. I hope I was able to answer your questions on the TPS2121. If you ever have any more questions please reach out.

    Regards,

    Andy Robles