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Original question:

TS3A44159: TS3A44159 leakage from pin 11(NO4) to pin 14 (V+)

TS3A44159: Leakage from NO pin to NC, COM and VCC when board is not powered

Duong Nguyen
Prodigy 70 points
Part Number: TS3A44159
Other Parts Discussed in Thread: TMUX1574

I have the same issue with: https://e2e.ti.com/support/switches-multiplexers-group/switches-multiplexers/f/switches-multiplexers-forum/968039/ts3a44159-ts3a44159-leakage-from-pin-11-no4-to-pin-14-v?tisearch=e2e-sitesearch&keymatch=TS3A44159#

When I plug UART to USB module to the unpowered board. TXD and RXD will come to NO pin of TS3A44159. I measure voltage in NO, NC, COM is around 1.8V and voltage in VCC is around 0.6V.

So I have 2 questions:

1. Why voltage in NO can pass switch and go to both NC and COM ports?

2. I checked in datasheet and I see IK - Analog port diode current only have a negative value -50mA. As my understanding, It means TS3A44159 NC, NO, COM pin only have a ESD diode connect to GND, and do not have ESD diode to VCC. So what is the path of leakage between NO pin and VCC pin ?

  • 0
    TI__Genius 10974 points

    Hi Duong,

    As also mentioned in that post you referenced, the TS3A44159 does not have powered off protection which means that if there is a voltage on the NO/NC/COM pins and it is greater than the VCC by 0.5V, you will forward bias the ESD protection diode between the NO/NC/COM pin to VCC and it will essentially backpower the device. See the app note below reviewing this concept and if you need a 2:1x4 channel device with this feature, you can look at the TMUX1574.

    https://www.ti.com/lit/an/scda015c/scda015c.pdf?ts=1662991766367&ref_url=https%253A%252F%252Fwww.google.com%252F

    Thanks!

    Bryan

  • 0 in reply to Bryan Marshall
    Prodigy 70 points

    Thank Bryan for your response.

    Could you answer question 2? 

    If TS3A44159 have the ESD diode which connects to VCC. I think IK - Analog port diode current should be both positive and negative value?

    Is it correct?

  • 0 in reply to Duong Nguyen
    TI__Genius 10974 points

    Hi Duong,

    I am going to look into this one a bit further and get back to you with an answer within the next day or two.

    Thanks!

    Bryan 

  • +1 in reply to Bryan Marshall
    TI__Genius 10974 points

    Hi Duong,

    Apologies for the delay on this, but wanted to investigate this more to understand what may be happening. You are correct that there is no diode between the I/O and VCC, however,  there is an internal FET that can get inadvertenly turned on due to the architecture of this device when there is a condition of the I/O pin voltage being greater than the VCC voltage by 0.6V (the body diode of one of the transistors gets forward biased). Hence, this will create a path that goes to VCC and then to the adjacent NO/NC/COM pin.

    To be clear, the use case that is demonstrated here violates the datasheet and should not be used in such a manner. You would still want to pick a device that has powered off protection to avoid such situations from occurring if you will not be able to power the device prior to putting a voltage on the input pins.

    Thanks!

    Bryan