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AMC1300: Maximum differential input voltage

Igor Kaminski
Prodigy 10 points
Part Number: AMC1300
Other Parts Discussed in Thread: STRIKE, , TPD1E10B06, AMC1311, AMC3330, AMC1350

Hi,
For last month I've been working on isolated amplifiers. Now I'm trying to design proper input protection.

The " Absolute Maximum Ratings" section specifies maximum values, but I'm missing maximum differential input voltage, which won't cause any damage to IC. Is it protected only with antiparallel diodes and limiting current will do the job?
With indirect lighthing event the voltage can easily exeed 320mV. Will it cause any pernament damage to IC? What's the maximum value?
Unluckily, with higher differential voltages the LTSpice simulation got crashed many times.

Thank you

Best Regards
Igor

  • 0
    TI__Guru**** 175371 points

    Hi Igor,

    Welcome to our e2e forum!  The MAXIMUM input voltage you can apply to the AMC1300 is as you noted in the table of section 7.1.  In normal use, one of the inputs of the AMC1300 is tied to your input ground (see Figure 51) and the other input would then swing +/- 250 mV (linear range, +/- 320 mV clipping) about that ground node.  For surge protection, like in the case of lightning strike, you would have to use an external protection diodes.

  • 0 in reply to Tom Hendrick
    Prodigy 10 points

    Thank you for your reply!

    I use the AMC1300 for voltage measurment (need of differential input). I use voltage divider using {Rin}/2 with R15/16 and {R4}. Wih this configuration I can easily achieve proper maximum voltage at the D1 (regulated by value of R15/R16) (D1 is bi-directional) with proper voltage for AMC (250mV max).

    The problem is that, even if I can regulate normal operation maximum differential voltage (e.g., 5.5V max at the D1 for TPD1E10B06), the the diode start to clamp at 8V which will result in clamp voltage 363mV (8V/5.5V * 250mV), which will easily exceed 320mV.

    What will be efficient protection in this design? Is there any possibility to use TVSes instead of flat-clamp devices? Will placing low voltage Schottky diodes at the input will do the job?

    Best regards
    Igor

  • +1 in reply to Igor Kaminski
    Guru 140200 points

    Hi Igor,

    clipping does not mean damage.

    This is the absolute maximum ratings referring to the input voltage:

    Please show a complete schematic of your input circuitry of AMC1300. I think there's a mistake.

    Kai

  • 0 in reply to kai klaas69
    Prodigy 10 points

    Thank you for reply

    kai klaas69 said:
    clipping does not mean damage.

    That's what I was trying to understand.
    I tought, that clipping will result in damaging the IC.

    kai klaas69 said:
    Please show a complete schematic of your input circuitry of AMC1300. I think there's a mistake.

    There are only two diodes for each pin connected to Vcc or to Vee, RC filter (10mA resistor limitation) and it's directly connected to INP and INN

  • 0 in reply to Igor Kaminski
    Guru 140200 points

    Hi Igor,

    the AMC1300 is optimized for current shunt measurements. It shows a very high input bias current of 30µA typical which can make issues in a voltage measurement with a high resistance voltage divider. The AMC1311 might be better suited, as it offers an input bias current of only 3.5nA typical.

    Kai

  • 0 in reply to kai klaas69
    Prodigy 10 points

    Hi Kai klaas69,

    That's the issue I was thinking about. That's why I added Vref with voltage of 2V to "pulled up" the voltage to 2V where the bias current is the lowest.
    Unluckily, the AMC1311 is 0-2V range single-ended input, that's why it requires differential to single-ended converter (op amp with 1V vref to achieve offset). It also needs negative power supply, which will assure that I don't exceed specific swing voltage.

    Do you think that additional input buffer can help in this design?

  • 0 in reply to Igor Kaminski
    Guru 140200 points

    Hi Igor,

    the AMC3330 could work, or the brand new AMC1350.

    Kai

  • 0 in reply to Igor Kaminski
    TI__Guru**** 175371 points

    Hi Igor,

    As Kai mentioned, the AMC3330 might be an option for you.  It has a differential input with +/-1V full scale range.  It also provides power to the high side which can save you from having to add an isolated power supply.  The AMC1350 matches the footprint of the AMC1300, and it has a +/-5V input range.