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AM26LV31: about VOD

? ?
Prodigy 10 points
Part Number: AM26LV31

Hello, may I ask a question about AM26LV31.

My backend servo control differential input requires a VT value between 2.5-3.8V,

1) May I ask if the differential output voltage of this chip can meet the requirements. I have confirmed the datasheet, it seems to be only 1.5V?

2) I tested the output of AM26LV31IDR on my test substrate, and the differential voltage measured using a differential probe was actually 3V Is there any difference between the content on the datasheet and what is it? Is my test inaccurate?

3) This chip is powered by 3.3V, and the same AM26LV31E is also 3.3V. I feel that the VOD of the latter is much larger. Why?

thanks

  • 0
    TI__Mastermind 46537 points

    Hi,

    1. No I wouldn't use this part because with how we spec this device the VOD could be as low as 2V so if it doesn't have enough drive strength we'd point to that value in the datasheet. 

    2. The datasheet includes test setups for the tests and if yours don't match then we don't guarantee behavior - also typical measurements aren't guarantees and the min/max values are across the tested range. Depending on how you are loading the outputs - a standard typical measurement with very little load current is going to be closer to VCC. Our test uses a 100 ohm load between differential outputs as that is how a RS-422 bus is supposed to be setup - this is a RS-422 device.  

    3.  It really depends on how you are loading the device - if you are measuring open circuit voltage it may not be crazy to see that level. However if you want to send me a picture of the top of the unit so I can check to see if its legitimate I can - while I don't think there is necessarily an issue it's quick for me to check. 

    Ultimately I wouldn't use this part, or any RS-422/RS-485 device (they will all have the same issue - RS-485 may be slightly better but not enough to guarantee performance), if you need that high of a voltage threshold unless you have some type of line driver near the receiver to boost the voltage to ensure that you are at the correct levels because there is risk that you will drop under the need Vt levels of the application you are pursuing. 

    Best,

    Parker Dodson