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DS10CP152 Questions?

Henry Jung
Prodigy 220 points

DEAR. ALL

When a disable high-impedance state?

During operation, how states of when disable ?

  • 0
    TI__Mastermind 29655 points

    Hi Henry,

    I tried out the DS90CP152EVK on a bench and was able to verify the behavior of the DS90CP152 when the input is disabled.

    The receiver inputs of the DS90CP152 do not have internal fail-safe biasing. For point-to-point and multidrop applications with a single source, fail-safe biasing may not be required. When the driver is off, the link is inactive. If fail-safe biasing is required, this can be accomplished with external high value resistors. The IN+ should be pull to Vcc with 10kΩ and the IN− should be pull to Gnd with 10kΩ. This provides a slight positive differential bias, and sets a known HIGH state on the link with a minimum amount of distortion.

    When I tried to measure the resistance from IN+ to VDD or IN- to VSS when the input is open and the device EN = L, the ohmmeter showed a high-Z impedance, and the output voltage is fixed around the  Vcm = 1.2 V. When the input is open and device EN = H, ohmmeter also shows high-Z impedance from IN+/- to VDD/VSS, respectively. The output is in an unknown voltage state.

    Below are scope captures under the following conditions:

    Input Open, EN = L (Disabled)

    Input Open, EN = H (Enabled)

    Input = 200 MHz, 800 mVpp signal, EN = H (Note that scope impedance was measured at 1 MOhm instead of 50 Ohm, so value of differential amplitude is effectively doubled)

    Does this answer your question?

    Thanks,

    Michael

  • 0 in reply to Michael Lu (Santa Clara)
    Prodigy 220 points

    Input = 200 MHz, 800 mVpp signal, EN = L(disable)

     output Status?  high-Z impedance?

  • 0 in reply to Henry Jung
    TI__Mastermind 29655 points

    Hi Henry,

    In this case, the output is held at the common mode offset voltage:

    200 MHz, 800 mVpp signal, EN = L

    Thanks,

    Michael

  • 0 in reply to Henry Jung
    TI__Mastermind 43795 points

    Henry,

    The DS10CPxxx, DS10BRxxx, DS25BRxxx, and DS25CPxxx family of LVDS devices have the following characteristics.

    Input Impedance.

    EN = L or H

    Termination = 100 ohms differential

    For LVDS the output driver sets the input common mode voltage.  So these devices will be Hi-Z to VDD or GND in either case, but there will always be a 100 ohm impedance from IN+ to IN-.

     

    Output Impedance.

    EN = H (output enabled); Termination = 100 ohms differential

    EN = L (output disabled); Termination = Hi-Z

     

    Regards,

    Lee