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INA901-SP: Micro amp range Current Sense in High Voltage

Part Number: INA901-SP
Other Parts Discussed in Thread: INA240-SEP, INA190


I'm designing a high voltage board which has a voltage output around 400VDC. I also need to monitor the current and my load will draw about 60 micro amp. I found TI Circuit Note SBOA295_June 2018 (High-voltage, high-side floating current sensing circuit using current output, c ) and planning to follow it to sense current on high voltage.

I'm looking for Rad-Hard current sensing IC that can sense current in micro amp range. I simulated INA901-SP before and did not think it would work in micro amp range. Do you have any rad-hard amplifier that can sense current in micro amp range? Thanks

  • Hi Erica,

    Thanks for using E2E! This is going to be a challenging use case for our portfolio. There's a few challenges/issues with this approach:

    - The biggest care about you need to be looking for here is the input bias currents of the device you select, as it is going to have direct bearing on your accuracy. For the INA901, this is typically 8uA, and can be all the way up to 19uA over temperature and lot to lot variation:

    These current ultimately flow with the load current and into the device, with the IN- current also passing over the shunt resistor. This means that if you are trying to measure 60uA in application, the inputs bias current from the IN- leg could result in almost 33% error here, before considering any other forms of error (offset, gain, drift, etc.). At the moment, we only have two rad-hard offerings (we also have the INA240-SEP), but the INA901 is the lower Ib here. 

    - The application you found (SBOA295) uses a current output device to pedestal up to the 400V via a transistor on the output (and the zener/resistor combo on the input). To effectively use this, the device you choose needs to be a current output device, which sadly there are not many of on the market, and TI does not offer any in rad-hard capabilities. It will increase the complexity of the solution, but you can use SBOA358 to alter a voltage output current amplifier to a current output, and then proceed with SBOA295 around that schematic. Let me know if this makes sense. 

  • I was thinking to use SBOA295 with INA901-SP. When I simulated INA901-SP using LTspice, it can go to mA range not micro amp range. 

    If I follow SBOA358 then SBOA295, I still need a Rad-hard current sensing amplifier that can measure in micro amp range, is that correct? I found INA190 which has Input bias current of 3nA max, but I guess there is no Rad-hard version. Is there another way to do?

  • Erica, 

    That is correct. Adopting SBOA358 is only for the purposes of transducing the output from voltage to current so that the output may float over the 400V common mode. You would still need to find a current sense amplifier that meets the needs of 60uA measurement, which I agree, INA901 is not the best fit for. 

    INA190 is an ideal device for measuring this level of current, but unfortunately this device is not available in a rad-hard option.