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AM26LS31: AM26LS31

Ravi Kumar Gaddala
Prodigy 20 points
Part Number: AM26LS31
Other Parts Discussed in Thread: AM26LV31E, AM26C31, AM26LV31, SN74LVC2G66, UCC27517

Tool/software:

Hi TI E2E Team,
Good morning. 
We (R&D Dynamics) are using "AM26LS31-Quadruple Differential Line Driver (PDF attached)" in one of our projects. We would like to know the Typical and Maximum values for "High-level output voltage of AM26LS31."  
Thank you. Looking forward to hearing from you. 
Regards,
RaviDifferential_transceiver.pdf
  • 0
    Guru 275790 points

    Typical values are shown in figure 5-6.

    The maximum is not specified. For a differential protocol, what matters is the differential output voltage; the AM26LS31 is guaranteed to output at least ±2 V over a 100 Ω termination.

    The AM26LS31 is an old, bipolar device supported only for legacy applications. Consider the AM26C31 instead, or the AM26LV31E for a 3.3 V supply.

  • 0
    Prodigy 20 points

    Thank you, Clemens. But we are looking to get a 5V at the output. Could you please suggest any parts? Thank you. 

  • 0 in reply to Ravi Kumar Gaddala
    TI__Guru 57770 points

    Ravi,

    These devices are built around the RS-485/422 standard. The standard states the output driver should be able to generate a voltage of atleast 1.5V across a 54 ohm load. For manufacturers (like TI) we try to build parts with margin to exceed the 1.5V minimum, generally around 2.2V minimum. The part that Clemens suggested (AM26LV31) has an output of 3.1V typical which is very high for an RS-485 device. I don't think theres an rs-485 device on the market that can output 5V with a Vcc=5V because there will always be a voltage drop loss across the schottky diodes. 

    -Bobby

  • 0 in reply to Ravi Kumar Gaddala
    Guru 275790 points

    Any normal CMOS logic device has rail-to-rail outputs, but smaller drive strength. What load current do you require?

    Do you actually need differential outputs, or just a positive output?

  • 0 in reply to BOBBY
    Prodigy 20 points

    Thank you, Bobby for the detailed information. Actually, Gate driver needs 5V signal but the output of differential transceiver is 3.1V (as you stated above). So, can we connect the output of transceiver to the input of gate driver as their voltage levels are mismatched? 

    Clemens: We are using differential transceiver in the interface board and it is low current may be 150 mA max. We need differential outputs.  

    Thanks to both of you. 

  • +1 in reply to Ravi Kumar Gaddala
    Guru 275790 points

    If I understand you correctly, you have two gate drivers, and you want two complementary 5 V signals.

    This can be done with a plain logic buffer and an inverter. You can minimized skew between them by using two gates on the same chip, e.g., SN74LVC2G66.

    Please note that there a gate drivers with complementary inputs (e.g., UCC27517), so you could control two of them with the same signal.