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TCAN1462-Q1: Output Impedance Difference

Mark Philip Felipe
Genius 11160 points
Part Number: TCAN1462-Q1


Hello,

is my understanding correct, that during "power down" (=VCC or VIO is below the threshold) on the bus only the leakage current I_LKG(IOFF) "appears"?

Is my understanding correct, that in "standby" (=VCC and VIO available, STB = VIO) the receivers input resistance R_IN is connected to GND on each bus line?

Is there a way to make the bus lines high impedance other than in "power down"?

  • 0
    TI__Guru 59767 points

    Hi Mark,

    Yes your understanding is correct similar to table 8-2 of the data sheet, showing all the possible conditions for high impedance.

    Hence, similar to the table, you may ensure VIO is high and VCC is low for High-Z, thanks.

    Best Regards,

    Michael

  • 0 in reply to Michael Ikwuyum
    TI__Genius 11160 points

    Hi Michael, some follow-up


    * What exactly does High-Z mean (in the datasheet)? Is this only the I_LKG or also a biasing to GND? A bit more of differentiation between the states (including "protected") in table 8-2 might be necessary according chapter 8.4.3 or table 8-5 (standby with biasing to GND?, unpowered with I_LKG only?).
    * Assuming VCC = STB = GND, VIO = TXD = 3.3V, which output impedance (leakage current) is visible on the bus?
    * Assuming VCC = GND, VIO = TXD = STB = 3.3V, which output impedance (leakage current) is visible on the bus?

    Thank you.

  • 0 in reply to Mark Philip Felipe
    TI__Guru 59767 points

    Hi Mark,

    • High impedance implies the device is not actively driving the bus. Your understanding is correct. The ILKG data sheet spec (5 uA) is for when VCC and VIO = 0 V.
    • Your conditions suggest <UVcc and >VIO. Hence, we can estimate the leakage in the protected mode with VCC/2 and RIN. I.e., for 5 V Vcc for example, 2.5 V / 20 K ~ 125 uA.
    • For standby, the data sheet specs 0.1 V VO_STB (biasing to GND) mainly implies (2.5 V - 0.1 V) / 20 k ~ 125 uA due to other nodes on the network realistically driving the bus to recessive. If no node is driving the bus to recessive, 0.1 V / 20 k ~ 5 uA would be realistic, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 40 points

    Hello Michael,

    I will be taking over the questioning from Mark - thank you Mark for writing the questions here.

    Sorry for asking again, but the differentiation between "high impedance" states according to the datasheet (including table 8-2) is still confusing, as it only mentions a "high impedance", but I ask myself (or want to have it confirmed again) when only the leakage current I_LKG(OFF) according chapter 6.8 is available without the biasing to GND.

    Can you please check and confirm or correct the following table:

    VCC

    VIO

    STB

    Device Mode

    Bus State

    >UVCC

    >UVIO

    GND

    Normal

    per TXD

    VIO

    Standby with Wakeup

    R_IN to GND

    <UVCC

    >UVIO

    GND

    Standby without Wakeup

    R_IN to GND

    VIO

    Standby with Wakeup

    R_IN to GND

    >UVCC

    <UVIO

    Any

    Protected with VCC

    R_IN to GND

    <UVCC

    <UVIO

    Any

    Protected without VCC

    I_LKG(OFF)

     According to your previous answers, there is a difference between the two “protected” states (according to table 8-2, where three “protected” states are mentioned, but they seem to be different according).

    Hope you can help me with that – and in case of an update of the datasheet, a more detailed specification might help the users in the future.

    Thank you and best regards,

    Steffen

  • 0 in reply to Steffen
    TI__Guru 59767 points

    Hi Steffen,

    Your understanding is correct. High impedance implies the leakage would be minimal i.e., 5 uA (higher impedance) or 125 uA for example. 5 uA for when both VCC and VIO at GND as you mentioned and the estimated 125 uA for the other RIN to GND conditions for example. Hence, customers are typically not concerned on how high the impedance is as long as the bus is not actively being driven by the bus, thanks.

    Best Regards,

    Michael.