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SN65C1168E: Replacing the HD29051FP

R.Fukunaga
Expert 2435 points
Part Number: SN65C1168E
Other Parts Discussed in Thread: SN65C1168, SN751178, THVD1500

Tool/software:

Hi all,

To replace the HD29051FP used as the RS-422 driver/receiver

We are considering using the SN65C1168E.

We replaced the SN65C1168E in the same environment as the HD29051FP and measured the waveform, and found the following difference.

We also checked the output waveform with the simulation tool. We confirmed similar overshoot and undershoot when a capacitive load was connected. We did.


1) Is the overshoot and undershoot caused by the capacitive load?
Is it possible that the same occurs with the SN751178NSR instead of the SN65C1168 E?

2) Is the overshoot and undershoot caused by the output current?
The output current of the SN65C1168E is ±20 mA, and the output of the HD29051FP is ±40 mA.
I think the output current of the SN751178NSR is ±60 mA. Does it not occur with the SN751178 NSR?

I would appreciate any comments.

Best Regards,

Ryusuke

  • +1
    Guru 316440 points

    The SN65C1168E is faster than the HD29051FP; it is likely that the overshots are caused by this.

    It appears that your data rate is much lower than 10 Mbps. For such signals, I would recommend a transceiver with slower output edges like the THVD1500, but there is no such integrated device for 2+2 channels. It might be possible to add resistors and/or ferrite beads to slow down the edges; please show the schematic.

  • +1
    TI__Guru 72161 points

    Hi Ryusuke,

    Clemens is correct. If you have a faster driver (rated for high speed) and a lightly loaded bus you are more likely to see overshoots/undershoots.

    The signal itself doesn't look like it has any signal integrity issues so I don't see any immediate concern.

    If you want to slow down the edges, you could also try placing a cap between the differential pins, maybe try 100pF first. You could also try a device that supports slower speeds.

    -Bobby