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AMC1351: IN Pins Range

Francis Jiang
Expert 4620 points

Part Number: AMC1351

Hi Team,

What's the input range of IN pins? Considering VDD1 is 3.3V.

Why there is 15V max value in datasheet? Is it a error? Thanks.

a20942f2-0844-446d-afcc-931c060e80db.png

BRs,

Francis

  • +1
    TI__Expert 7620 points

    Hi Francis,

    The 15V is the absolute maximum rating.  For normal device usage, please refer to the Recommended Operating Conditions.

    Thanks.

  • +1
    TI__Guru 61222 points

    Hi Francis. 

    This is the absolute maximum specification. 

    Operation outside the Absolute Maximum Ratings may cause permanent device damage. Absolute Maximum Ratings do not imply functional operation of the device at these or any other conditions beyond those listed under Recommended Operating Conditions. If used outside the Recommended Operating Conditions but within the Absolute Maximum Ratings, the device may not be fully functional, and this may affect device reliability, functionality, performance, and shorten the device lifetime

    Please see the next section for recommended operating conditions, V_FSR.

  • 0 in reply to Alexander Smith
    TI__Expert 4620 points

    Hi Alexander, Saleh,

    Thanks for your prompt reply, well noted.

    So if customer uses 3.3V as VDD1, the analog input pins' range are 0~3.3V, right?

    BRs,

    Francis

  • +1 in reply to Francis Jiang
    TI__Expert 7620 points

    Hi Francis,

    The full-scale input range of the device is -0.25 to 5V for the VDD1 range of 3-5.5V.

    Thanks.

  • 0 in reply to Saleh Ahmad
    TI__Expert 4620 points

    Hi Saleh,

    Thanks for your reply.

    May I further ask why this device input can exceed the supply power? Doesn't this internal op-amp saturate?

    BRs,

    Francis

  • 0
    Prodigy 10 points

    The power supply range of VDD1 is 3-5.5V. When using a 3.3V power supply, what is the input range of the IN pin? Or can it operate normally within the 0-5V range? Please explain, and provide relevant test data.

    Also, I would like to know if the IN pin input voltage is greater than 5V, will it experience forward saturation, or will it still operate normally (taking a 6V input as an example, is the output 6V*0.4=2.4V or 5V*0.4=2.0V)? Please provide answers.

  • +1 in reply to Kolt
    TI__Expert 7620 points

    Hi Francis/Kolt,

    Due to the internal structure of the device the internal op-amp inputs don't see the voltage on the INP pin.  It gets divided down down by the op-amp's resistor network.

    Once the INP pin exceeds the full-scale voltage (VFSR), the output will still change, but with degraded performance and higher non-linearity, especially near the clipping voltage (Vclipping).  Once you increase the input past the clipping voltage (Vclipping), the output will be clipped.

    Thanks.

  • 0 in reply to Saleh Ahmad
    TI__Expert 4620 points

    Hi Saleh,

    Sorry for trouble again, I have a quick question here:

    Based on the BD, the internal amplifier +IN should be the same with GND1, so whether I can calculation the theoretical range of INP through (Vout's range / 0.4 gain)? If use 3.3V VDD1, and consider the amp is RIRO, the max input of INP is 8.25V? 

    And the figure shows Vin linear range is 6.25V, so the internal amplifier is not RIRO, right?

    BRs,

    Francis 

  • +1 in reply to Francis Jiang
    TI__Expert 7620 points

    Hi Francis,

    I'm not sure if the internal amplifier is RIRO, but the output of the first internal amplifier is not directly related to the output voltage.  The first amplifier scales the input for the input of the modulator feedback loop.  In the modulator, stage the analog input is converted to a bitstream of 1's and 0's, and then sent over the isolation barrier.  On the other side of the isolation barrier the bitstream goes through a filter which converts it back to an analog signal.  If you are interested in how the delta-sigma modulator part works in detail, you can take a look at these videos: Precision labs series: Analog-to-digital converters (ADCs) | TI.com

    Francis Jiang said:
    And the figure shows Vin linear range is 6.25V

    In the plot it's hard to tell the nonlinearity visually, but at some input voltage >5V (it will be very close to the Vclipping edge) the nonlinearity increases and then the output clips.  The exact point where this happens changes slightly device to device and over conditions like temperature.  

    Thanks.