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Machine Model & Human Model

Aamir Ali
Expert 2525 points

-> I have seen in many datasheets, specifying machine model, human body model & charged model , what do dey mean? How can any device sustain such an high voltage. Is it for short duration only?

-> In opamp, if I connect 2V to its inverting or non-inv directly & in other case via 10K resistor? How do dey different. Opamp have very high resistance so adding a resistor , how do it affects

  • 0
    Guru 21975 points

    Aamir,

    The different ESD models attempt to model the effect of a electrostatic charge discharging into a integrated circuit pin. The human body model is a 100pF capacitor in series with 1500 ohms. The machine model is 200pF in series with a 500nH inductor. In each case, the capacitor is charged to a voltage level, then discharged into the tested pin of an IC. Special internal clamp and protection circuitry in the IC is designed to dissipate this discharge event without damage. Most ICs could not survive a continuous high voltage but can survive a pulse with the limited energy stored in the capacitor.

    Your second question may depend on the specific circuit configuration of an op amp. A resistor is sometimes placed in series with an input terminal to equalize the DC resistance at both inputs of an op amp. Assuming that the input bias currents of both inputs are equal, the offset voltages produced by equal resistances are equal and cancel. This so-called "bias current cancellation resistor" is often misapplied and counterproductive. Details depend on the specific circuit configuration an op amp. This is explained in the video in the link below:

    http://focus.ti.com/general/docs/video/Portal.tsp?lang=en&entryid=0_nifgb34h

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Expert 2525 points

    Bruce,

    Thanks for your explanation.

    -> Gain of inv amp is -(Rf/R1). Now selecting Rf:R1= 1K:100ohm produces gain of 10. similarly values like 10K:1K,. 50K,5K etc produces same effect. How does they are different from each other? How to select best suited value.

    -> In open drain comparators, can I select volatge at o/p pull supply less than or greater than supply voltage?

  • 0 in reply to Aamir Ali
    Guru 21975 points

    Aamir,

    The input resistance of an inverting amplifier is equal to the input resistor. Making this resistor value too low places a heavy load on the input source voltage. It also makes the effective gain sensitive to the impedance of the source voltage because the source impedance adds to the resistance of the input resistor. Making the resistor values too high increases the noise of the application. High resistor values can also cause problems with frequency response and stability. The best choice is often a compromise that depends on the requirements of the application.

    Open collector or open drain comparators can have a pull-up voltage less than the supply voltage. Most types can have a pull-up voltage that is larger than the power supply. Check the detailed specification on any particular comparator to assure that this is the case.

    In any future questions, please begin a new posting for each unrelated question. This allows others to search and find information according to the title of the posting.

    Regards, Bruce.