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TS5A23157: Behavior when unpowered

Austin Allen
Intellectual 2355 points
Part Number: TS5A23157
Other Parts Discussed in Thread: TS5A23159

Tool/software:

We have a question about the behavior of the part when it is unpowered i.e. Vdd=0V and the following scenarios:

  1. Can In1, In2 be driven by another GPIO when device is unpowered
  2. In1, In2 is connected to 0V, nc1,2 is floating and no1,2 is at 1.8V. What is the voltage and current and COM1,2
  3. In1,In2 is at 3.3V, no1,no2 is floating and nc1,nc2 has 1.8V
  • 0
    Guru 272990 points

    1. Yes; see [FAQ] Can the input voltage (Vi) to my logic device be higher than the supply voltage (Vcc)?

    2./3. A closed switch behaves like a resistor. COMx will also be floating.

  • 0
    TI__Expert 7365 points

    Hello Austin,

    I don't recommend applying voltage on the device, while it is unpowered. It may damage it or cause it to behave unpredictably. 

    I can't predict device behavior that exceeds its operating conditions. 

    What is the application here? What are you trying to accomplish? 

    Thanks,

    Nir 

  • 0 in reply to Nir Gilgur
    TI__Intellectual 2355 points

    Hi Nil,

    How does your comment here reconcile with the FAQ that Clemens shared above? It sounded like there was a "Partial Power Down Protection" in this case?

    I will connect with you offline with more details.

    What about if the supply is off?

    There is one more possibility for the input being a higher voltage than the supply, which is the case where the supply is off (Vcc = 0V) and the input is operating at some voltage higher than 0V.  This case is covered partially by the above information, but also has a special feature associated with it called "Ioff - Partial Power Down Protection."

    If a device is rated for operation with Vcc = 0V, the Electrical Characteristics table will include the value of Ioff, which is the leakage current into any input or output pin of the device when the supply is forced to 0V. Note that this spec is _only_ valid under the case that the supply is at 0V, and not just if the supply is disconnected (floating) or off (unknown voltage). Some supplies can still provide enough voltage to operate a device even though they are disabled -- for example, many boost converter circuits have a direct connection from the input voltage to the output through only a diode.

  • 0 in reply to Austin Allen
    TI__Expert 7365 points

    Hello Austin,

    The TS5A23157 doesn't have Ioff circuitry and partial power down protection, it is not indicated in the datasheet. A device with partial power down feature will have it mentioned in the features section in the datasheet. 

    This an example from the SN74CBT338C datasheet. 

    I might be able to recommend a device that will fit your application, if you can please elaborate on what the specifications are.

    Thanks,

    Nir

  • 0 in reply to Nir Gilgur
    Guru 272990 points

    Sorry, I was overlooking that the device is unpowered. Without power, the switch is not closed. There are clamping diodes to VDD, so the 1.8 V at the I/O pins can damage the device.

    If you want to be able to apply I/O voltages to an unpowered switch, use a device with the "powered-off protection" feature like the TS5A23159. When unpowered, the I/Os are floating.