INA283-Q1: Measure the high voltage 100-200VDC 1mA-2A

Hello again,

So overall using the resistor divider approach to bring down the input VCM for INA283 (or any other CSA) is not a recommended solution. It does bring down the VCM, but it reduces the overall circuit gain and introduces large error that would have to be calibrated out. If this approach is chosen, then there needs to be thorough error analysis that considers variation in bus voltage, 499k resistors, the differential input resistance (Rdiff) of INA283, the variation in INA283 input bias currents (IB), and how all of these could vary over temperature. Ideally, you could calibrate every circuit on every power up at least for offset and then make sure calibrated error is less than what your system allows. You can reduce the effect of the input resistor error by reducing the 499kΩ’s, but this will come at the expense of power losses from resistors. I recommend experimenting in simulation (TINA-TI or PSPICE for TI) to see if there is a feasible solution with tolerable error. You can also choose a higher gain device such as INA285 (1000 V/V) so the input resistors bring the total gain to something still usable (~15 to 20V/V).

ina283e2e.TSC

Note in the simulation schematic I added a large input capacitor at INA283 input because device will need this in real world to help maintain a stable input voltage. For more information I recommend the following video:

https://training.ti.com/ti-precision-labs-current-sense-amplifiers-input-filter-error

The other options to extending VCM range are:

1. Use isolated solution
   1. TMCS1100/TMCS1101 or TMS1107
   2. Isolated amplifiers such as AMC130x
      1. https://www.ti.com/isolation/isolated-amplifiers/overview.html
   3. Isolated ADCs
      1. https://www.ti.com/isolation/isolated-adcs/overview.html 

2. Float and power a CSA (configured as current-output) with a Zener diode and level-shift the output using a FET/BJT
   1. This document shows how to do it for a unidirectional current
      1. https://www.ti.com/lit/ug/tidu833/tidu833.pdf
   2. This Figure 17 of following document shows how to measure bi-directional current of current-output modified CSA.
      1. https://www.ti.com/lit/an/slya047/slya047.pdf
   3. These documents show how to convert any voltage-output CSA into a current-output
      1. https://www.ti.com/lit/an/sboa358/sboa358.pdf
      2. https://www.ti.com/lit/an/sboa513/sboa513.pdf

3. Float a digital power monitor (e.g., INA226 or INA228) and isolate the digital bus line with a digital isolator
   1. This document shows how to do it: 
      1. https://www.ti.com/lit/ug/tidu361a/tidu361a.pdf
   2. Here is where to find a digital isolator:
      1. https://www.ti.com/isolation/digital-isolators/overview.html 

You can also use two CSAs one to measure positive and the other to measure negative current , but this will require either two ADC inputs (one for positive and the other for negative) or one ADC input for the current and another ADC/GPIO input to know which way the current is flowing.

Hope this helps.

Best,

Peter