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LSF0102: pull up resistor for push-pull and open-drain

Hardy Xue
Expert 3640 points

Part Number: LSF0102

Hi Team,

My customer has some question for our LSF0102. I watched LSF training video and still have some questions as below.

customer's application: interface maximum frequency is 24MHz, 3.3V to 1.8V / 1.8V to 3.3V.

1. For push-pull transmitter, do we need to add pull up resistor on B side (3.3V) to support 48Mbps data rate? Or, LSF0102 can easy to support 200Mbps data rate on push-pull transmitter application?

2. Customer's system can config transmitter and receiver as push-pull or open-drain. Therefore, there are 8 scenarios need to analyze. Could we add 200 ohm pull up resistor for B side and 4.7k ohm pull up resistor for A side? If no, could you please help to correct my comment if I am wrong? Thank you. 

    a. Up translation / Tx_push pull / Rx_push pull: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

    b. Up translation / Tx_push pull / Rx_open drain: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

    a. Up translation / Tx_open drain / Rx_push pull: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

    a. Up translation / Tx_open drain / Rx_open drain: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

    a. Down translation / Tx_push pull / Rx_push pull: B side don't need to add 200 ohm RpuB, LSF0102 still can support 48Mbps data rate. A side need to add 4.7k ohm RpuA to limit maximum sink current.

    a. Down translation / Tx_push pull / Rx_open drain: B side don't need to add 200 ohm RpuB, LSF0102 still can support 48Mbps data rate. A side need to add 4.7k ohm RpuA to limit maximum sink current.

    a. Down translation / Tx_open drain / Rx_push pull: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

    a. Down translation / Tx_open drain / Rx_open drain: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

Best regards,

Hardy

  • 0
    TI__Expert 3640 points

    Sorry for updating question 2:

    2. Customer's system can config transmitter and receiver as push-pull or open-drain. Therefore, there are 8 scenarios need to analyze. Could we add 200 ohm pull up resistor for B side and 4.7k ohm pull up resistor for A side? If no, could you please help to correct my comment if I am wrong? Thank you. 

        a. Up translation / Tx_push pull / Rx_push pull: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

        b. Up translation / Tx_push pull / Rx_open drain: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

        c. Up translation / Tx_open drain / Rx_push pull: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

        d. Up translation / Tx_open drain / Rx_open drain: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

        e. Down translation / Tx_push pull / Rx_push pull: B side don't need to add 200 ohm RpuB, LSF0102 still can support 48Mbps data rate. But add 200 ohm RpuB still okay. A side need to add 4.7k ohm RpuA to limit maximum sink current.

        f. Down translation / Tx_push pull / Rx_open drain: B side don't need to add 200 ohm RpuB, LSF0102 still can support 48Mbps data rate. But add 200 ohm RpuB still okay. A side need to add 4.7k ohm RpuA to limit maximum sink current.

        g. Down translation / Tx_open drain / Rx_push pull: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

        h. Down translation / Tx_open drain / Rx_open drain: B side need to add 200 ohm RpuB to support 48Mbps data rate and A side need to add 4.7k ohm RpuA to limit maximum sink current.

  • 0 in reply to Hardy Xue
    Guru 327650 points

    See the FAQ entry 5.2 in the Voltage-Level Translation With the LSF Family application report.

    You should always use a push/pull transmitter, then you never need a pull-up on the transmit side.

    You should always use a pull-up resistor on the receive side. What resistor value you need to achieve a certain speed depends on the total capacitance of the traces and connected devices.

    A receiver does not output a signal and therefore cannot be configured as push/pull or open-drain. I do not understand what you are referring to.