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TS3A4751: What happens to NO1-4 when Vcc=0V

Go Bravos
Expert 6090 points
Part Number: TS3A4751
Other Parts Discussed in Thread: SN74CBTLV3125

Hi team,

Since the TS3A4751 is a normally open switch, would it be valid to say that when VCC= 0V,  NO1-4  would be disconnected(Hi-Z) from COM1-4?

Thank you.

  • 0
    TI__Mastermind 45495 points

    Go,

    Here is an excerpt from the switches and multiplexers FAQ page regarding that "normally open" doesn't really mean anything for a solid state switch.

    The TS3A4751 device is not defined when Vcc = 0V so it is not valid to say that when VCC= 0V,  NO1-4  would be disconnected(Hi-Z) from COM1-4.

    What are you connecting in your system that you need Hi-Z when Vcc = 0V?

    There are parts that define a Hi-Z state when Vcc=0 V and you can filter for the feature powered off protection on ti.com switch selection tool.  Searching for 4-channel 1:1 switch with this feature provides the SN74CBTLV3125 which is commonly used for SPI and JTAG signal isolation.

    Thank you,

    Adam

     

  • 0 in reply to Adam Torma
    Prodigy 20 points
    1. The control signals (IN1-4) will also be 0V, so there would not be a bias voltage on the gate (VGS < Vth).
    Does this mean the NO1-4 would not be connected to COM1-4?

    2. I want to make sure the one side of the switch is isolated from the other when VCC=0V and IN1-4 = 0V.
    Please confirm that if they are not connected(isolated), this mean that the power from one side (COM1-4 side) of the switch would not power-up the circuitry through these pins on the other side of the part (NO1-4) .

    3. Would the only draw on the powered-up side of the switch be the part leakage?
    Off leakage (ICOM(OFF) = 10na
    ON leakage (Icom(ON) = 3na max)
    Do we know if the part leakage would be the ON or OFF leakage?
  • 0 in reply to Richard Cundiff
    TI__Mastermind 45495 points

    Richard,

    1) Event if the control signals are 0 V the TS3A4751 is not defined to be Hi-Z if Vcc = 0V.  It is possible that with Vcc = 0V and a voltage on the COM or NO pins can backpower the device through the ESD protection diodes and accidently bias the gate of the FET.  More information can be found in this e2e post.

    [FAQ] Do I need powered-off protection? (HI-Z when Vcc = 0V) - Switches & multiplexers forum - Switches...

    e2e.ti.com
    Watch this TI Precision Labs training video to understand how powered-off protection works with your system. This tech note has detailed information on powered

    2) It is not guaranteed that the TS3A4751 can isolate the I/O path with Vcc = 0V.  Devices with this guarantee will have the powered off protection/ ioff/ partial power down feature stated in the datasheet including a spec with the leakage when Vcc = 0V. 

    3) I'm not sure I understand this question.  The off leakage specification in the TS3A4751 is when Vcc is powered up and the control logic pins are set to turn off the FET.  This off leakage will demonstrate how well the part isolates the signal path with the control logic set to turn the switch off.  The on state leakage is when Vcc is powered up and the control logic is set to turn on the FET and there is a low impedance path from COM to NO.  This leakage is measuring how much current doesn't make it from the input to the output.

    As stated above the SN74CBTLV3125 will be able to isolate the signal path with Vcc = 0V.  What signals are you isolating and why do you need to isolate them with out power to the switch?

    Thank you,

    Adam