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INA110 for high side measurement

Idan Ozana
Intellectual 480 points
Other Parts Discussed in Thread: INA110, AMC1100, DRV421, DRV411, DRV401, DRV425

Hi,

My name is Idan and I'm electronic engineer.

In my application, I need to measure low voltage from serial shunt resistor (0.2Ω) that connected between DC-DC converted from one side (300VDC/ 4A) and a full bridge inverter and parallel big capacitor in the other side (High-side measurement).

For that purpose, I thought to use the INA110 as the first stage and then ISO120SG Isolated amplifier as a second stage (both with ±15V) but in order to do so I need you to clearly the following questions:

  1. Is it possible to implement this suggestion in a 300V High-side measurement? Do I need a floating power supply reference to the lower leg of the shunt resistor?
  2. In page 9, COMMON-MODE INPUT RANGE, you mentioned that the differential input signal and its associated common-mode voltage should not cause the output of A1 and A2 (input amplifiers) to exceed approximately ±10V with ±15V supplies. In normal operation that is not a problem because the differential voltage is 0.8V so with fix gain configuration of x10 I will not exceed the ±10V. However, during start up, it is possible that I will have differential voltage of 300V for several seconds(due to the large capacitor) (no common mode due to floating supply).

The question is if I'm using a clamping diode to ±15V (as in FIGURE 14), is the circuit protected (Common mode, differential voltage and so on)? Maybe I need to connect the clamping diode to ~1V (in order make sure that A3 input will not "See" more the ±10V with fix gain of 10).

  1. In the INA110, FIGURE 14 you mentioned that for high voltages you recommend of R1 = R2 = 100kΩ. Did you mean "high voltages" during normal operation or at overvoltage protection such as start up to 300V? Why do I need such large values? Only to protect the 2N4117A clamping JFET diode?   

My second option is to use the AMC1100 amp…

Thanks a lot,

Idan

 

 

  • 0
    TI__Genius 15760 points

    Hi Idan,

    Thanks for your question. We will be reviewing it next business day.

    Regards

  • 0
    TI__Genius 15760 points

    HI Ian,

    I was reviewing your question today and realized you have specific questions about the INA110. I will move this question to the Precision Amplifier group so they can assist you with the specific questions you have related to datasheet circuits. 

    Regards

  • 0
    TI__Mastermind 25825 points
    Hello Idan,

    My recommendation is to either use low-side sensing or indirect sensing (e.g. fluxgate/hall-effect sensors). While you could use the AMC1100 for a high-side measurement with 300V common-mode, the device would get damaged when the inputs get pulled apart by 300V. You would have to therefore design a robust input protection scheme that clamps the differential input voltage and limits the current that can flow into the device. Same holds true for the INA110, but you would definitely have to clamp the common-mode voltage because it should not exceed the supply voltages.

    If you can sense on the low-side, a simple op amp circuit would work because the common-mode voltage is near ground. If not, please consider devices such as the DRV401, DRV411, DRV421, and DRV425 (this one is particularly interesting to me). Though I do not support the DRV devices, if you have any applications questions regarding them I can point you in the right direction.