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DS90LV047A: And other LVDS/RS232 components (DS90LV047, DS90LT012, TRSF3232)

Peter Osucha
Prodigy 20 points
Part Number: DS90LV047A
Other Parts Discussed in Thread: TRSF3232, TRS3227E,

I am using the parts mentioned above to provide LVDS signaling over a long length of Cat5E cable (4 signals total).  The LVDS segment seems to work well.  Two of the signals originate from a laptop using a standard serial port - RS232.  I believe to accurately get the RS232 signals to a format for using the LVDS circuit, I need a component like your TRSF3232 part.  I've included a schematic showing the connections of the 3 parts mentioned.  Connector J1 is the db9 header that connects to my laptop serial port.  Then the RS232 interface chip, then you can see the LV047 and LT012 chips.  Connector J2 over on the right is an RJ45 connector that has the LVDS outputs.

Before I make the test PCB to try this, I wanted to confirm (or at least get your opinion) that the circuit I have shown is what is expected for RS232/LVDS interfacing.

Sincerely,

Peter

  • 0
    Guru 281410 points

    Looks OK.

    You are not using two channels, so the TRS3227E might be more appropriate.

  • 0
    TI__Guru 59470 points

    Hi Peter,

    Going from RS232 into LVDS is a little unusual since the LVDS portion will be limited by the RS232 bandwidth (seems like this isn't a concern for you). In most cases I see, usually if LVDS is chosen, it is LVDS from the sender to receiver to take advantage of the faster bit rate, lower power consumption, and lower EMI. In your case, you will be mixing single ended signaling with differential.

    From the LVDS device's point of view, it does not care what is connected to the singled ended side (DIN of DS90LV047A) as long as the signal input is within the recommended operating conditions defined in the datasheet. The RS232 device's Rout pin looks like it should meet the requirements to drive within the recommended operating conditions. The DS90LV047A will easily support the RS232 bitrate (you would be limiting yourself to 1Mbits here since the RS232 driver is the slower of the two).

    One minor note is for PCB trace, the LVDS trace impedance is generally 100 ohms and you should try to impedance match both traces (+ and -). 

    As Clemen's pointed out, you do have unused channels and may want to switch the RS232 part out with a lower channel count one.

    -Bobby