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TMUX154E: TMUX154E

seunghui lee
Prodigy 20 points
Part Number: TMUX154E

Hi TI E2E design support team

While I was choosing appropriate Mux for my system, I got a question regarding powered off protection.

Since SN74LVC1G3157DSF doesn't recommend to apply any signal to input when there's no VCC due to its clamping diode, I was planing to use TMUX154e because of powered off protection function.

However, I couldn't find detailed information or logic about powered off protection anywhere else than its title.

What I only assumed about protection function is that TMUX154e still has parasitic clamping diode but EN pin is doing something with it.

Then, of course, another question comes up to me how EN logic can work when there is no supplying voltage.( maybe that's why it's logic low active pin ?)

Hope I can get elaborated info about Powered off protection and can assure the situation like some signal is applied to input pin when there's no VCC.

If i'm missing anything from the datasheet please let me know.

Thanks

  • 0
    Guru 316690 points

    The absolute maximum ratings allow voltages above VCC at the control inputs at all times, and at the I/O pins when VCC = 0.
    (The control pins do not have positive clamping diodes; the I/O pins deactive them when the power is off.)

    The EN pin does not work without power. When the device is powered off, all switches are off (open).

  • 0
    TI__Genius 10552 points

    Hi Seunghui,

    The team is currently on holiday. Please allow until Monday next week for a response here. 

    Regards,

    Alex

  • 0
    Prodigy 20 points

    Hi, Thank you for the quick reply.

    Just another question following to that, how did IO pins deactive positive clamping diodes?

    have a good holiday! 

    BR,

  • 0
    TI__Genius 10552 points

    Hi Seunghui,

    Thanks for reaching out here! So for starters, I'd like to link an application brief on powered off protection since you mentioned you couldn't find detailed information about it. 

    You're correct that EN logic is functional without a supplied voltage due to it being logic low - though I want to note the pin should still be tied to ground and not left floating. 

    Due to the IP of this feature, you can be assured that the device won't be damaged when a signal is applied to the I/O pins when no VCC is present. 

    Regarding how I/O pins deactivate the clamping diodes - the pins themselves don't deactivate the diodes exactly. When the VCC pin is not powered, the SEL and EN signals have no effect on the MOSFETs, and the I/O pins are disconnected from each other. This is because the MOSFETs have a threshold voltage, which is the minimum voltage required to turn on the switch. If the voltage across the gate and the source of the MOSFET is lower than the threshold voltage, the MOSFET is off and no current can flow.

    Hope this helps!

    Regards,

    Alex

  • 0
    Prodigy 20 points

    Hi Alex Vish,

    Thanks for the reply, It helps me a lot.

    However, there's some explanation that confused me. I guess my question was not clear enough.

    Here are my understandings about powered off case. 

    1) SN74LVC1G3157DSF has parasitic diode between Vin to VCC, so even though MOSFET's channel is disconnected since VCC is below Vth there is current path to VCC from Vin 

    refered : 

    https://e2e.ti.com/support/switches-multiplexers-group/switches-multiplexers/f/switches-multiplexers-forum/1294154/sn74lvc1g3157-sn74lvc1g3157/4910388#4910388 

    2)TMUX154E removed this parasitic diode somehow as Clemens Ladisch said above

    But what confused me was that in the last comment, I/O pins are secured because of the channel disconnection not because of removing or isolating diode.   

    So the questions are that 

    1) is it channel disconnection or removing(isolating) diode that makes Vin pin High Z when there is no VCC?

    2) if it's removing diode, how can it be when the diode is parasitic. 

    3) if it's not removing diode, is it just circuitry function that the protection IP has?

    Best Regards,

  • +1 in reply to seunghui lee
    TI__Genius 10552 points

    Hi Seunghui,

    Sorry for the misunderstanding here! So at a fundamental level, the inner workings of the protection circuity for I/O pins are due to the exact IP you mention. The mechanism of which can't be readily shared. 

    For the first point, maybe I'm misunderstanding the question. Are you wanting to confirm that the device won't be damaged when a signal is applies to either I/O pins or control pins when VCC=0V? If that's the case, then as long as you follow the abs max ratings, the device will be OK. 

    seunghui lee said:
    Hope I can get elaborated info about Powered off protection and can assure the situation like some signal is applied to input pin when there's no VCC.

    Regards,

    Alex

  • 0 in reply to Alex Vish
    Prodigy 20 points

    Hi Alex!

    Thanks for the confirmation and letting me know the current confidential status of the protection IP.

    Now everything is clear to me

    Best Regards,

    SH lee