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Original question:

DP83822I: State of Internal Pull-up and Pull-down state

DP83822I: Why are there some difference of SCH between KSZ8041 and DP83822I ?

Eggsy Pang
Expert 4985 points
Part Number: DP83822I

Hi Team,

Compared with KSZ8041 SCH, link https://www.microchip.com/DevelopmentTools/ProductDetails/PartNO/KSZ8041NL-EVAL, I found there some difference of SCH between KSZ8041 and DP83822I.

1. Our DP83822I pin TXP/TXM and RXP/RXM need to pull-up 49.9K to 3.3V, while KSZ8041's pins pull-down 49.9K and 0.1uF to GND. Why cause this difference? What is effect of 0.1uF here?

2. In DP83822I TIDA or EVM SCH, transformer pin CT connect 3.3V with 1uf and 0.1uf cap, while in KSZ8041's SCH, transformer pin CT connect 3.3V with just one 10uf Electrolytic cap. Why cause this difference?

3. In DP83822I TIDA or EVM SCH, transformer pin 10 and pin 15 connect 75Ω with 0.01uf cap to GND, while in KSZ8041's SCH, transformer pin 10 and pin 15 connect 75Ω with 1000pf cap. Why cause this difference? 

4. In DP83822I TIDA or EVM SCH, transformer isolate GND1 and DP83822I GND2 connect with 4700pF cap, while in KSZ8041's SCH, transformer isolate GND1 and KSZ8041 GND2 connect with 1000pF cap. Why cause this difference?

Thanks!

  • 0
    TI__Mastermind 23675 points

    Hi Eggsy,

    I cannot speak for KSZ, but I can for the 822.

    A1) we need 50 ohm to 3.3V because we are using a current mode line driver and those are our termination resistors. They need to be very accurate in impedance to create an accurate voltage swing.

    A2) Center tap is to 3.3V with a few caps to limit supply noise. Cap values are a recommendation, but can change depending on the system.

    A3) We are using a bob smith termination. You can change around the capacitance if you would like.

    A4) The value can be changed around depending on what you see as performing better for your system application.

  • 0 in reply to Ross Pimentel
    TI__Expert 4985 points

    Hi Ross,

    Thanks for your great support!