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INA181: Is the current sense amplifier ok to measure the voltage of resisitor voltage divider as AMC1301 does in the enclosed circuit.

Part Number: INA181
Other Parts Discussed in Thread: AMC1301, , INA186, INA190, INA230, INA220

Hi,

Is the current sense amplifier ok to measure the voltage of resisitor voltage divide as AMC1301 does in the enclosed circuit.

If not true ,could you please show me the really differnece among the input stages of  current sense amp,instrument amp and isolated current sense amp?

If true,what are the tips to do it better?

Thank you!

FYI.The attached circuit says the isolated current sense amp AMC1301 can be optimized to be used in resistor divider voltage sensinge application.

  • Hello User,

    Thank you for your question! Our engineers will analyze and respond when we return to the office on Monday.

    Best regards,

    Ian Williams
    Applications Manager
    Current Sensing

  • Hello Ian,

    Thank you for your quick reponse.Looking forward to your team's professional suggestions.

    I would like to share my reuirement in detail by email.Please write a email to me if he or she need more information.

    Best regrads,

    Sean

  • Hi,

    I wouldn't do this. The INA181 is optimized for very low resistances between its inputs. See sections 9.1.2 and 9.1.3 of datasheet of INA181.

    Kai

  • Hi Kai,

    Thank you for the information.

    So INA186 or INA190 or most of the instrumentation amplifier with very low bias current would be ok to measure the voltage of resisitor voltage divider(the value of resister to divide the voltage is lower than 1k ohm).Am I right?

    By the way,how about INA220 or INA230 which have ability to measure the current and voltage in one package?

    At last ,my requirement for  you reference.I want to measure 60Hz AC sinewave current(0.05~10A, rms) and voltage(1~600V.rms).no isolation needed for the measurement circuits.

    Best regards,

    Sean

  • Hello user6282468,

    There actually is not too much difference between these devices when it comes to the front end. They both contain differential input impedance followed by a differential or difference amplifier. For the AMC1301, the input differential impedance is 18kΩ typical (when VINN=GND, or low-side sensing) and for the INA181 it is 2.5kΩ typical with ±15% variation over process variation and temperature.

    The input bias currents (IB) for both parts are negative (flows out of the input pins) when input common-mode voltage (VCM) is 0V (low-side sensing). For the AMC1301, the IB is -30 µA typical and for the INA181 it is -6 µA typical.

    When using input shunt resistors with relatively high resistance, you will generate gain and offset error. The induced gain error is the result of the relatively small input differential impedance of the devices. The induced offset error is the result of the micro-Amps of input bias current. Both of these induced errors can be calibrated out for both devices. In general, offset due to IB (Vos_IB) = IB* Rshunt.

    So to answer your question: yes, the INA181 can be used to measure the low-side voltage off a resistor divider shown in Figure 52 of AMC1301 datasheet; however, the INA181 will have more gain error since the input impedance is smaller and thus it will become more important to perform a two-point gain calibration for every device.

    ---

    Now to address the other design questions and challenges: the INA190/INA186 devices are high-input impedance, current-sense amplifiers (CSA) so they can measure higher shunt resistances with negligible effects on accuracy. Increasing the shunt resistor past 1kΩ, the effects of the shunt resistor loading down the ~4MΩ input impedance of the INA190 may become noticeable. Additionally, the nano-Amps of IB will begin to create significant offset.

    The input impedances of the INA220 and INA230 are more complex since these are an ADC front-end. In general, it is not recommended to use these digital devices to measure voltage across high resistance shunts.

    Lastly for you final requirement of measuring AC current, I would note that the input VCM of any device cannot exceed its Absolute Maximum rating. I am not sure how you plan to measure a 600Vrms with the INA181, but the only way to practically do this is to float the devices supply voltage with the input VCM. Given the VCM is AC you would probably need a full-bridge AC to DC rectifier circuit to supply the 5V Vs to INA181. You can message me directly on E2E if you would like to share schematic and design information through this.

    Sincerely,

    Peter

  • Hi,Peter,

    I gave you a private message with the block diagram.

    Your are appreciated to make the questions even clear.

    Sincerely,

    Sean

  • Hi Sean,

    the advantage of a current sense amplifier like the INA181 is that you can measure the voltage drop across a shunt in the presence of a large common mode voltage, because the INA181 offers an outstanding common mode rejection ratio of 100dB typically. But if you mount a resistive voltage divider at the input of INA181 which is referenced to signal ground in order to measure a high voltage you don't need the briliant common mode rejection of current sense amplifier at all. So, why not using a standard OPAmp for the voltage measurement?

    Kai

  • Hi,Kai,

    There are two main reasons I want to try it.

    1 We need to measure the current and voltage separately or both in our products.We want to use the compatible circuit to make the PCB layout easy and share one PCB.

    2 Precision Op ams with lower Vos and drift are always expensive  and You need control the errors of resistors outside.

    Sincerely,

    Sean