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DS90C189-Q1: Pull down resistor and unused pin

yf liao
Expert 1080 points
Part Number: DS90C189-Q1

Hi, I have two questions on DS90C189-Q1:

1. For those pins stated "includes pull down", what's the value of the pull down resistor? 

2. We want to use one board to drive two different LCD where one requires channel A and B LVDS output, another LCD only requires channel A. It looks to me that channel B LVDS output cannot be terminated on our board even when they are not used. This may violate the recommendation in the datasheet, so could you adivse possbile solutions to have a comaptible design on interface these two LCDs?

What's the consequence of leave channel B output open when they are not used?

  • 0
    TI__Guru** 103215 points

    Hello YF,

    We will need a day or two to find the answers and will respond back shortly. Thank you for your patience

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    TI__Intellectual 2930 points

    Hello YF,

          Pulldowns are implemented using active pulldowns. This means pulldown behavior of a Resistor is emulated using transistors. This is a nominal value of 40K but over different parts, voltage and temperature, this could vary between 10K to 80K.

    For the unusued Display, are you using the Mode pin to program it to a single LVDS output port? You could leave the output port floating , but if the device is programmed into Dual mode, the unterminated output would be putting out signals; This could have potential EMI implications at the system level if the board is not well shielded

    Thanks

    Vijay

  • 0 in reply to Vijaya Ceekala
    Expert 1080 points

    Hi Vijay, thanks for your reply. We plan to have pull up and pull down resistor on some pins(such as VODSEL) with DNP configuration on different boards,  It looks like that an external 10Kohm pull up resistor may not be strong enough in the case that the internal resistor is 10Kohm, what value will you suggest?

  • 0 in reply to yf liao
    TI__Intellectual 2930 points

    Hello YF

      Suggest a 2K resistor

    Thanks

    Vijay