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AMC1306M05: Questions of PADC products

Moon Wang
Intellectual 1285 points
Part Number: AMC1306M05
Other Parts Discussed in Thread: AMC1336, AMC1400

I have been learning some of PADC products recently. I have a few questions and I would like to seek your guidance and explanation. Below are the questions I would like to inquire about:

1. The input resistances (Rin) of AMC1303 and AMC1306, which are used for current sensing, are specified as 19k and 4.75kΩ, respectively. However, the input impedance of AMC1336 and AMC1333, which are used for voltage sensing, can reach up to 1.5GΩ. Based on experience, current sensing can be equated to voltage sensing across the shunt resistor, and this voltage value is often only in the range of tens to hundreds of millivolts. In theory, a larger input resistance would be desirable. Therefore, I would like to understand the reasoning behind choosing these parameters in the design.

2. There is a distinction between "reinforced" and "basic" in our isolation products. I would like to know which parameters are used to differentiate these two categories.

3. Our AMC1400 product is designed with an ultra-wide body. I would like to know the major advantages of such wide packaging for isolation products.

Thank you very much for your time. I look forward to your response.

  • 0
    TI__Expert 8876 points

    Hi Moon,

    Thank you for your questions!

    1. For voltage-sensing applications, a high input resistance is preferred to support low gain-error signal sensing in high-voltage applications using resistive dividers. In current sensing applications, this high input resistance is not required, so a low input resistance is used, which reduces associated device costs.
    2. This FAQ helps explain the difference between basic and reinforced isolation.
    3. The ultra-wide body has more creepage and clearance. The app brief, TI’s First Isolated Amplifiers With Ultra-Wide Creepage and Clearance, explains: "Improved and wider packages prevent degradation along the package surface and arcing through the air between pins, which ensures isolation quality."

    I hope this helps!

    Best,

    Samiha

  • 0 in reply to Samiha Sharif
    TI__Intellectual 1285 points

    hi Samlha,

    thanks for your reply! Could you please explain in detail why high input impedance is not required for current sensing? 

    best wishes,

    Moon

  • +1 in reply to Moon Wang
    TI__Expert 8876 points

    Hi Moon,

    Sure! My understanding is that in voltage sensing applications, we use resistor dividers with large resistances to divide down high voltages. In order to avoid gain error, the input resistance of the device should be similar. This creates a preference for voltage sensing devices to have a high input resistance. In current sensing applications, this is not the case, so high input resistance is not necessary. This cookbook circuit is a good example of why we prefer high input resistance devices for voltage sensing applications:  https://www.ti.com/lit/an/sbaa350a/sbaa350a.pdf

    Best,

    Samiha