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AMC1351: regarding fail-safe

Johnson David
Prodigy 80 points
Part Number: AMC1351

Tool/software:

Dear.Ti Team

We tested AMC1351 fail safe mode.

We are using AMC1351 as single-ended. (VOUTN = short to GND)

When VDD1(VDD IN) is off(0V) and VDD2(VDD out) is ON(3.3V), VOUTP(V(fail-safe)) is measured approximatly 150mV (GND).

In datasheet, when fail-safe mode (VDD1 undervoltage or missing), V(Fail-safe) will be -2.57V. 

I want to know if the result I measured is correct.

So, I'd like to know why the -2.57V of the data sheet doesn't come out and 150mA comes out.

Please let me know.

Best Regards

  • 0
    TI__Guru 51221 points

    Hi,

    VOUTN is a driven output and therefor should not be directly shorted to GND. Please consider a 10kohm resistor in series between VOUTN and GND to limit the output current. 

    Furthermore the specified, fail-safe output voltage is a differential measurement which will not be possible to measure in this configuration. 

  • 0 in reply to Alexander Smith
    Prodigy 80 points

     Dear. Alexander Smith

    If I pull down VOUTN, it will no longer be differential, so I could be able to measure it using a single probe on the oscilloscope. right?

    In this case, I'd like to know what would be the measured Vfail-safe value of VOUTP

    Thank you for your assistance.

    Best regards,

    Johnson

  • 0 in reply to Johnson David
    TI__Guru 51221 points

    Hi Johnson,

    As I understand from your original post, you are directly connecting VOUTN = GND2 and therefor not measuring differentially. Is this not the case? 

    Perhaps you can share a schematic and oscilloscope plots showing the behavior you are describing?