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Original question:

TMUX1209: Muxes keep breaking without warning

TMUX1209: Component randomly stop working from one measure and another

Gabriele Vegetali
Prodigy 10 points
Part Number: TMUX1209
Other Parts Discussed in Thread: TMUX6209, TMUX7309F

Tool/software:

Hi, i developed a measurement circuiti in which the TMUX1209 is used to change the reference resistance of the circuit and so also to change the current flowing in the sensing resistance in order to let the voltage across it be always in a good position regarding the ADC dynamics and so increasing resolution.

Sometimes the TMUX1209 just stop working from one measure to another (i turn off the power supply of the entire circuit and then turn it on again between two consecutives experimental measure protocols), and also the strange thing is that sometimes it stops connecting the input  Dx to the 4 outputs (S1x, S2x, S3x, S4x) independently on the selectors configuration even if the enable pin is set to 3.3V so high voltage level,that means the MUX should work properly; while other times it connects the input Dx to all the pins simultaneously, so without considering the selectors configuration.

I let the schematic of the entire circuit below here in this post in order to let you understand and debug it from hardware point-of-view:

as you can see, in top left, there is the power supply part, then in the bottom let, there are two BME280 readout and communication circuits, while the entire circuit on the right is the one in which the TMUX1209 is inserted and provides the already explained function together with an opamp

if you have any idea on what is leading us to change continuously a TMUX1209 and provide us a solution to reduce the problem and try to avoidi it in future, i will be very grateful

if you need more details just ask freely, thank you very much for your availability and for your support

Kindly regards

Gabriele

  • 0
    TI__Mastermind 24430 points

    Hi Gabriele,

    Happy to help here on the debug.

    The first thing I wanted to see is if there is a possibly of voltages being present on the io pins when the MUX is 0V.

    This device doesn't have a feature called  powered off protection that can potentially lead to damage when voltage is on the io pin when VCC=0V.

    Please let me know what you think of this idea and I can look into this more.

    Regards,

    Kameron

  • 0
    Prodigy 10 points

    Hi Kameron,

    in this moment i do not have the device setup near to me, so i am not able to provide you the exact values of voltages present on the io pins when the MUX is 0V (not power supplied), but i did these tests and verifications many times before asking on this forum as i saw on the internet that this one could be a serious problem for this device; this tests certified that the votlages are very near to 0V (not more than 5mv).

    Before purchasing it, i read the datasheet and chose this specific mux (TMUX1209) also because in a section, it mentioned about a fail-safe logic circuity that is properly used to avoid these problems and issues about voltages higher than Vcc pin when MUX is off (0V), as i develop personally the PCB and it is still an experimental version, i wanted to be sure to buy a device able to survive to any situation that would have happened in the circuit (like the one that is solved by the fail-safe logic unit).

    i am still trying to find a solution, even if it would be to reproject the circuit or purchase another type of MUX; if you could help me understand better the situation, i would be very grateful, so i can solve the fact of continuously substitute the component in the PCB.

    thank you, i wait for your response to clear all the situation.

    kind regards

    Gabriele

  • +1 in reply to Gabriele Vegetali
    TI__Mastermind 24430 points

    Hi Gabriele,

    Thank you for this additional information.

    What I now think is going on is something in the design is causing the TMUX1209 to have a latch up event.

    This could be the reason why the switching of the TMUX1209 stops working in your design and for example all of the s pins connect to d pin at the same time.

    During a latch-up event a multiplexer internal switch transistors can get stuck in a conducting state and therefore we can lose the ability to switch between the inputs with controller logic.

    Here is a application note I think will do a better job of explaining this topic but a good multiplexer to test in your redesign might be the TMUX6209 which is latch up immune and shouldn't have the same issues as the TMUX1209 with latch up.

    Also just so I can try to have more information is there a possibility that your input signal is ramping faster than your supply?

    Gabriele Vegetali said:
    (i turn off the power supply of the entire circuit and then turn it on again between two consecutives experimental measure protocols)

    Please let me know what you think and we can discuss this further.

    Regards,

    Kameron

  • 0 in reply to Kameron Hill
    Prodigy 10 points

    Hi Kameron,

    Thank you for the fast response you gave me.

    I understood what can be the cause of the TMUX1209 stop working, in particular it seems your idea really fit my problem regarding the non-possibility to change configuration of the mux input-output connection through selectors.

    Thank you for the material and for the suggestions in order to change directly the component involved in the PCB.

    For what concern the last point and your request, i can not provide you sure informations and data about it (for example by means of oscilloscope analysis), but i think that all the signals are quite synchronous to each other; one thing i want to ask you is: if the signals instead are not so synchronized (so maybe some input ramp faster than the power supply Vcc pin, even with very small voltage difference), is there a possibility that also the TMUX6209 would stop working at a certain point?

    I ask you this, so I know if just substituting the component can be a final solution to all these issues, or instead I have to also re-project the circuit in order to be sure about it and improve its reliability.

    thank you very much for your availability and i wait your response

    have a good day

    Gabriele 

  • 0 in reply to Gabriele Vegetali
    TI__Mastermind 24430 points

    Hi Gabriele,

    Gabriele Vegetali said:
    one thing i want to ask you is: if the signals instead are not so synchronized (so maybe some input ramp faster than the power supply Vcc pin, even with very small voltage difference), is there a possibility that also the TMUX6209 would stop working at a certain point?

    So because the TMUX6209 has latch up immunity it should not stop working like the TMUX1209 is. That is it cannot get latched up like the TMUX1209.

    However the different ramp rates in your system could cause issues/potential damage with the TMUX6209 and it is best to make sure you do not violate the recommended operating conditions of the datasheet.

    The latch up immunity feature should help prevent issue in your application here but we cannot say definitively  as we don't know the exact voltage that will be present on the io pins and the supply with the asynchronous ramp rates as excessive overvoltage could mess damage the multiplexer 

    The best multiplexer our team has to help you reduce the possibility of issues in your design is the  TMUX7309F, which has overvoltage and power off protection which could eliminate the need to worry about power sequencing in your application.

    However in my opinion if the voltages difference between the io pins and supply is  small like 5mv- during power up  then TMUX6209 should be fine in as it should not get damaged and it has latch up immunity.

    Please let me know if this helps and if evaluating both the TMUX6209 and TMUX7309F is a option for you 

    Regards,

    Kameron

  • 0 in reply to Kameron Hill
    Prodigy 10 points

    Hi Kameron,

    thank you for your response and for clarification, also provided by a new possible solution.

    Kameron Hill said:
    However the different ramp rates in your system could cause issues/potential damage with the TMUX6209 and it is best to make sure you do not violate the recommended operating conditions of the datasheet.

    I will surely navigate with attention the datasheet in order to find some restrictions of the TMUX6209 that can arise possible issues when operating in my PCB.

    Kameron Hill said:
    The latch up immunity feature should help prevent issue in your application here but we cannot say definitively  as we don't know the exact voltage that will be present on the io pins and the supply with the asynchronous ramp rates as excessive overvoltage could mess damage the multiplexer 

    ok, I keep thinking that the difference between the ramp of the i/o pins is very slightly higher than the supply one, so i hope there is no problem for this point-of-view; furthermore, I read fastly the TMUX7309F datasheet and i noticed that the single supply limits are from 8V to 44V, unfortunately my circuit works at 5V, so i think the TMUX6209 would be a better choice for the power supply operating conditions (and also considering the update of the latch-up immunity with respect to the TMUX1209), please let me know what you think about it.

    finally, i thank you for all the advise you gave me in this chat and i will surely consider the evaluation and successive implementation of the TMUX6209 in order to solve latch-up events of the multiplexer.

    Waiting for your last idea about it, i wish you a good day!!

    Regars,

    Gabriele   

  • +1 in reply to Gabriele Vegetali
    TI__Mastermind 24430 points

    Hi Gabriele,

    Understood and yes for your application the TMUX6209 at 5V supply is likely the best solution here.

    Please let me know if you need any further assistance in the future as I can take a look into any future request you have about this topic.

    Thanks and Regards,

    Kameron

  • 0 in reply to Kameron Hill
    Prodigy 10 points

    Hi Kameron,

    thank you very much for all your support during this chat and for the numerous clarifications about this topic; these will surely enhance my knowledge in electronic devices and posible issues when developing and producing an home-made PCB.

    yes i am going to purchase some TMUX6209 and test them to understand if this is the solution to my problem.

    in any case, i will send you updates to let you know if it is all good or not.

    Regards,

    Gabriele