• State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 3 answers
  • Subscribers 65 subscribers
  • Views 188 views
  • Users 0 members are here
Support feedback
Options
Options

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.

TPS3840: TPS3840PL30DBVRQ1

Jose
Intellectual 315 points
Part Number: TPS3840
Other Parts Discussed in Thread: TLV840, TPS3808

Tool/software:

Hi,

We have designed a complex circuit in which we use the TPS3840PL30DBVRQ1.

After testing the circuit, it is fully functional.

In this circuit we use the MR pin to turn the device on and off, so the pin will spend a lot of time at High (device on), but also a lot of time at Low when the device is off.

The device may be switched off for periods of one month or more, meaning that the MR pin will be connected to Gnd via a switch during that time.


The questions are firstly whether this type of operation is suitable for the TPS3840, and secondly whether any additional measures need to be taken to prevent it from being subjected to external interference.

Thanks.

regards

Jose

  • 0
    TI__Expert 7100 points

    Hi Jose,

    Thanks for your question. I understand what you mean by device on and device off but I just want to clarify the MR (Manuel RESET) feature to be on the same page.

    The device needs to be on all the time, when MR is low the RESET will assert ( the RESET output will be low) without checking the VDD voltage level. And if MR is high, the RESET will depend on the VDD voltage level, and it will assert when VDD< Vth (threshold voltage). 

    As long as MR is low, the reset should be low. 

    Can you please provide more information on which application you are planning to use TPS3840. More specifically I'm trying to understand why MR pin will be connected to GND via a switch for months. I would like to understand if I can promote another device. 

    I hope this helps! Please let me know if you have further question.

    Best Regards,

    Sila Atalar

  • 0 in reply to Sila Atalar
    Intellectual 315 points

    Hi Sila,

    Thank you for your answer, and please find below the circuit concept.

    The manual reset will allow us to switch the equipment ON and OFF, and it will remain ON for long periods, and OFF also for long periods.

    The circuit can remain ON for several years, and OFF (switch closed in MR) for up to 6 months.

    The RESET output of the TPS3840 controls the power circuit switching ON and OFF.

    In addition, if the battery drops below the preset voltage, the unit will automatically switch OFF, so as not to discharge the battery.

    We've already added an external 100K pull-up resistor, and a small capacitor to the MR pin in order to avoid possible interferences.

    The circuit has been tested with the TPS3840 and the TLV840 and is fully functional, and we don't want to change it unless there is a very strong reason to do so.

    That's why we'd like your comments before we start manufacturing.


    regards

    Jose

  • 0 in reply to Jose
    TI__Genius 16491 points

    Hello,

    Due to the US holidays, our team will respond back the week of July 7th.

    Thank you for your patience.

  • 0 in reply to Masoud Beheshti61
    TI__Expert 7100 points

    Hi Jose, 

    Sorry for the delayed response and thanks for your patience.

    Your high level schematic seems good and TPS3840 can be a good fit. 

    I understand the purpose of 100k pull up resistor, I just want to highlight there is internal pull up resistor at MR pin. 

    The MR pin is intended to provide our customers the ability to control the output (not depending only on the VDD pin voltage level to assert the reset) ; they have the freedom to choose how they will design and control this pin.

    I hope this helps!

    Best Regards,

    Sila Atalar 

  • 0 in reply to Sila Atalar
    Intellectual 315 points

    Hello Sila,

    From your answer I conclude that there is no problem with having the MR pin forced to GND for very long periods.

    However, in the final phase of testing we found that our circuit has little hysteresis, because the circuit has to keep the battery disconnected when it is below about 11V, and switch the circuit on when the battery voltage rises above 12V.

    We saw that the SLVA360 document suggests a circuit with the TPS3808, but the price of this component is too high for our budget.

    We tried a similar concept with the TPS3840 but the circuit becomes unstable near the reset voltage.

    What other solutions do you suggest?

    regards

    Jose

  • 0 in reply to Jose
    TI__Expert 7100 points

    Hi Jose, I will be reaching out to via email to provide further assistance to you. 

    Best,

    Sila Atalar