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AM26LS32AC: Operation with only single ended PWM

Thomas Heilmeier
Prodigy 10 points
Part Number: AM26LS32AC
Other Parts Discussed in Thread: AM26C32

Hello,

I have a question regarding the AM26LS32AC. What happens if I only put a single ended PWM at PIN 1A, 2A, 3A and leave the PIN 1B, 2B and 3B open? I didn't find the information in the datasheet. Will it output only high level or will it output basically the same signal as the single ended input?

Thank you for your answers.

BR

Thomas

  • 0
    Guru 317370 points

    When you leave both A/B pins open, the output is high. But the behaviour for one open pin is not defined.

    Anyway, a differential receiver is a comparator. Connect the B pin to a reference voltage of half the maximum input voltage to make it behave like a buffer.

    The AM26C32 is a more modern device that uses less power.

  • +1
    TI__Guru 52462 points

    Hi Thomas,

    The behavior would be undefined in that situation. If you want to treat it as a single ended device - as Clemens mentioned, biasing the "B" pin to a set level as the receiver is just a comparator.

    What you set "B" bias voltage to is going to depend on how long the bus is, the resistance of the transmission line, and the frequency of the data signal. Essentially you just want to set "B" so that you can adequately pass 0's and 1's without adding any additional skew to the signals (i.e. if the voltage at the end of the transmission line at the receiver is 1V for a low and 3V for a high you'd want to set "B" pins bias to 2V so that you aren't adding any duty cycle distortion (moreso than just the device alone).

    Please let me know if you have any other questions!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 10 points

    Hi Parker,

    thank you for your reply. So when I generate a 5V PWM signal i can put that on Pin A and for having a 0V low and 5V high output voltage, I need to bias pin B with a constant 2.5V voltage. Is this correct?

    Best,

    Thomas

  • 0 in reply to Thomas Heilmeier
    TI__Guru 52462 points

    Hi Thomas,

    Yes that is correct - if the receiver is receiving 0V for low and 5V for high on "A" then keeping "B" at 2.5V will keep the device as a single ended one.

    Best,

    Parker Dodson