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AMC1302-Q1: 1st question: Connection between GND and INP allowed? 2nd question: Is the output voltage on AMC130xEVM centered on VDD2 or independent of VDD2?

Sally Mangalathu Arumana
Prodigy 415 points
Part Number: AMC1302-Q1
Other Parts Discussed in Thread: AMC1301, AMC1302

My customer raised 2 questions regarding AMC1302-Q1 to me.

1. Connection between GND and INP allowed?

It says on page 25 in the datasheet: "The floating ground reference (GND1) is derived from the end of the shunt,resistor, which is connected to the negative input (INN) of the device." That would mean TI indicates a need of GND1 and INN to be connected at all times. In Figure 56 the current is positive to load, which would mean that there is a negative differential input voltage between INN and INP and therefore would create a negative differential output voltage between OUTP and OUTN. The customer plans to have a positive current to load (similar to Figure 56) but result in positive differential output voltage instead. They want to connect INN behind R_shunt and INP before R_shunt. Then INP and GND1 would be connected which per datasheet does not seem to be a viable option. Could you let me know if that is really the case and if so why can INN only be connected to GND1 and not INP?

2. Output voltage on AMC130xEVM centered on VDD2?

In the user manual of the AMC130xEVM it says in 4.3 " The output voltage of the AMC130xEVM is centered on VDD/2 and..." That would mean in case VDD2 =3.3V the center of the output voltage would be 1.65 V, with VDD2=5V the center of the output voltage would be at 2.5V. Based on the datasheet of AMC1302-Q1 Figure 37 the center of the output voltage is always at 1.44 V which would be independent of VDD2. Could you comment?

Thank you in advance and kind regards,

Sally

  • 0
    TI__Guru**** 168605 points

    Hi Sally,

    The input is a differential connection so you can use either input to the AMC1302-Q1 (or AMC1301) referenced to GND1.  The output common mode is always 1.44 (typ) on the AMC1302-Q1 so we'll look into the EVM users guide and see if there is some correction to be made.

  • 0 in reply to Tom Hendrick
    Prodigy 10 points
    Hi Tom,
    I am the customer Sally mentioned.

    So thank you for the quick response.
    In your answer you refer to the AMC1301. But I am using the AMC1302-Q1. Chances are fairly big that this is valid for
    the 1302-Q1 too...just want to be sure here.

    So... is it the same for the AMC1302-Q1?
    And if so...why does TI , as point out in the datasheet, suggest that INN and GND1 needs to be connected?
    This is rather confusing for engineers who are used to differential amplifiers in general.

    Regards,

    Markus
  • 0 in reply to Markus Brenner
    TI__Guru**** 168605 points
    Hi Markus,

    Sorry for the typo (I'll change that), and yes, the same applies to the AMC1302. The section of the datasheet you are referring to is a "typical application" scenario as depicted in Figure 52 so the text in section 8.2.2 is describing that particular setup. I'll talk with the authors of the datasheet and see if there is some way to add a note in that section which clarifies that either input could be referred to GND1 so long as the common mode and absolute voltage levels and are maintained.