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AMC1411 have no VFAILSAFE

long zheng
Prodigy 30 points
Other Parts Discussed in Thread: AMC1400, AMC1411

I used 1400 1411 to measure voltage and current,

When 1400 input is suspended, 1400 can output -2.5V.

When the input of 1411 is suspended, 1411 outputs 280MV.

When the input of 1411 is connected to a resistor but not to a voltage, the output of 1411 is 0.0XV and there is no output of -2.5V


笔记

  • 0
    TI__Guru 50921 points

    Hi,

    I've copied below from the datasheet. I see in the schematic snippet that there is an additional connection from the input of the AMC1400, this may be pulling the input out of the common-mode input voltage range causing fail-safe output to occur. 

    The AMC1400 offers a fail-safe feature that simplifies diagnostics on a system level. Figure 7-2 shows the fail-safe mode, in which the AMC1400 outputs a negative differential output voltage that does not occur under normal operating conditions. The fail-safe output is active in two cases: • When the high-side supply is missing or below the VDD1UV threshold • When the common-mode input voltage, that is VCM = (VINP + VINN) / 2, exceeds the common-mode overvoltage detection level VCMov

  • 0 in reply to Alexander Smith
    Prodigy 30 points

    1400 is ok. 1411 have no vfailsafe

  • 0 in reply to long zheng
    TI__Guru 50921 points

    Hi,

    Fail-safe output should not occur with no input voltage applied, that is not the purpose of the feature. 

  • 0 in reply to Alexander Smith
    Prodigy 30 points

    in datasheet missing or below the VDD1UV threshold

  • 0 in reply to Alexander Smith
    Prodigy 30 points

    The fail-safe output is active in two cases: • When the high-side supply is missing or below the VDD1UV threshold

  • +1 in reply to long zheng
    TI__Guru 50921 points

    Hi,

    There is a difference in fail-safe output behavior for the two devices. 

    AMC1400: 

    • When the high-side supply is missing or below the VDD1UV threshold

    • When the common-mode input voltage, that is VCM = (VINP + VINN) / 2, exceeds the common-mode overvoltage detection level VCMov

    AMC1411: 

    • When the high-side supply VDD1 of the AMC1411 device is missing

    • When the high-side supply VDD1 falls below the undervoltage threshold VDD1UV

    • When the SHTDN pin is pulled high

    I have applied text to the schematic to clarify my understanding of the problem description:

    My understanding is that neither device is unpowered, meaning that both VDD1 and VDD2 = 3 to 5V. Therefor the missing or below the VDD1UV threshold is not satisfied. 

    However, I see that the AMC1400 has a trace connected to the positive input near R13. What is this trace connected to and what is the voltage potential? 

    If this trace has voltage, then the input of the AMC1400 may be pulled outside of the common-mode input voltage range which explains why it is outputting fail-safe output voltage. 

  • 0 in reply to Alexander Smith
    Prodigy 30 points

    I found the wrong place, thank you