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INA149: Comparison with current sense amplifier

user4811888
Intellectual 530 points
Part Number: INA149
Other Parts Discussed in Thread: INA148, INA146

Hi,

I have seen this part named INA149 belonging to differential amplifer, whose max common mode votlage can be up to 275V.

Could I learn the differences from current sense amplifier? these parts have only around 100V VCM max capability. Why not extend CSA to 275V?

  • 0
    TI__Mastermind 20130 points

    Hello, 

    In general this specification and others will depend on the process that the device is made on and the associated voltage and current limits for each process. 

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Intellectual 530 points

    Hi Chirs,

    thanks much for your answering, that means CM voltage up to such high would result in specific process option(actually only resisitor inside INA149 will suffer across high voltage), which might have poor performance and parameters, compared with current sense amplifier with much lower VCM presented above.

  • +1 in reply to user4811888
    TI__Guru 61790 points

    There are different circuit topologies used in current sense amplifiers (supported by a sensing product line) - some allow small current flow through the amplifier where the maximum input common-mode voltage (Vcm) is a function of the fabrication process used while others use a difference amplifier configuration (resistor network) similar to our INA149 where Vcm get attenuated by the large resistor ratio to be within the supply voltage used.   

    Thus, in case of INA149, +/-275V Vcm voltage gets divided by factor of 19k/(19k+380k) to be seen by the op amp as +/-13V (2V from +/-15V supply rails).  Similarly, using the maximum supply of +/-18V would allow INA149 Vcm of up to +/-336V (336V*19k/399k=16V) while for +/-5V supply the maximum Vcm is limited to just +/-63V (63V*19k/399k=3V) - the voltage directly on the input terminals of the internal op amp must be 2V or more from either rail.

  • 0 in reply to Marek Lis
    Intellectual 530 points

    Wonderful explanation, marek, appreciate it.

    By the circuit topologies of high step-down ratio of resistor network, actually it is the V+ V- supply voltage that determines VCM value.

    That means if somebody is willing to define a higher voltage supplyed current sense amplifiers, it can also achieve VCM up to 200V~300V.

  • 0 in reply to user4811888
    TI__Guru 61790 points

    Yes, Vcm in difference amplifiers like OPA149, INA148 and INA146 is a function of the power supply voltage and the internal attenuation ratio of the input resistors.  On the other hand, the current sensing amplifiers maximum Vcm is limited by the physical capability of the manufacturing process (like transistor Vce breakdown voltage) used for the implementation of the design.