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TS5A3167: Powered-Off Protection depending on V+

Ryan.Bishop
Expert 3900 points
Part Number: TS5A3167
Other Parts Discussed in Thread: TS5A3166, , TMUX1574

Hello,

I found this E2E post that talks about the TS5A3166: e2e.ti.com/.../660359

The applications engineer mentioned the powered-off protection works properly when V+ is pulled to 0V, but it does not work when V+ is simply removed from power and left floating. We also noticed that "Powered-Off Protection" was removed from the datasheet and the parametric table for TS5A3166. 

However, TS5A3167 still has "Powered-Off Protection" in the datasheet and parametric table. I was wondering if the Normally Closed architecture of this part prevents it from experiencing the same issue that the Normally Open TS5A3166 device has.

Thank you!
Ryan B.

  • 0
    TI__Mastermind 45340 points

    Ryan,

    The datasheet of both devices specify the powered off leakage when Vcc = 0V.  This means it will guarantee high impedance state under this condition.

    Can you describe the concern in your circuit?  Do you have a circuit that will have an issue if it is not isolated when Vcc = something other than 0 V? 

    What are you connecting to the switch? 

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    TI__Expert 3900 points
    Hi Adam,

    The switch would be used on the SPI link between an FPGA and a MCU. The MCU is always powered on but when the FPGA is powered down, it can't have voltage on the SPI lines. Therefore we are using the switch to isolate the FPGA while it's off.

    I'm worried that if power to the switch is just removed, and not actually pulled to 0V, that it could remain conducting.

    Is there a reason that "Powered-Off Protection" was removed from the TS5A3166 datasheet/product folder and not the TS5A3167 datasheet/product folder?

    Thanks for your help Adam!

    Regards,
    Ryan B.
  • 0 in reply to Ryan.Bishop
    TI__Mastermind 45340 points
    Ryan,

    I placed the TS5A3167 on my bench today and confirmed that if Vcc = 0V and 5.5 V is on the COM pin only 0.352 V shows up on the NC pin. This confirms powered off protection for this device.

    I also simulated your concern that if Vcc is removed by pulling the cord out of the power supply and saw that ~5.5 V was still observed on the multimeter connected to NC. This shows that there can be cases where there is no isolation if the Vcc pin is floating.

    The powered off protection spec is under the case when Vcc = 0 V so you can place a weak pull down resistor on Vcc to ensure that it is 0V when the power supply is removed.

    Also, the new TMUX1574 device is popular for SPI multiplexing and has better powered off protection performance.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Expert 3900 points

    Hi Adam,

    I really appreciate you taking the time to verify this on the bench! Those tests provide exactly the information I was hoping to learn.

    I mainly wanted to understand if TS5A3167 would behave the same as TS5A3166 in regards to powered off protection. It appears that they behave identically, so now I can ensure we design with it properly.

    Thanks again,

    Ryan B.