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THVD2410: THVD2410

Mike Simmons
Prodigy 10 points
Part Number: THVD2410

Tool/software:

I intend to use the THVD2410 as a RS422 Receiver only. I have external termination resistors configured to have a default "Low" input. My external resistor configuration is 120 Ohms between Inputs A and B, 715 Ohm pull-down on Input A, and 715 Ohm pull-up on Input B. What effect will the internal Fail-safe circuitry have on my circuit?  I'm expecting the Receiver Output to be "Low" for an Open-circuit bus condition and "High" for a short-circuit bus condition. The receiver will always be driven so the Idle bus condition is not an issue. Are my assumptions correct?

Thanks

  • 0
    Guru 277220 points

    Correct.

    If you want the output to be low in more conditions, consider exchanging the bus lines and adding an inverter.

  • 0
    TI__Guru 58160 points

    Hi Mike,

    Short answer is yes, their assumptions are correct.

    Longer answer:

    During an open bus, this would generate about 390mV from B to A . Since the voltage is from B to A, the device sees this as a negative value (A-B= -390mV). THVD2410 has Vth- as -200mV max so this ensures the device would see this as a minus logic (below Vth-). R output would be low during this condition. If you wanted the Routput high during open conditions you would put the pull up on A and the pull down on B.

    During a short circuit, A and B will be the same voltage, so the A-B=0V. Our device would see this as a voltage between the input fail safe threshold (Vth_FSH) and after ~18uS (tD(OFS) ) our device would enter the fail safe mode and R out would become high. 

    -Bobby