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INA253: INA253: unidirectional mode

Part Number: INA253

Hi,

I am designing where I have to measure current and I'll be using INA253. In unidirectional mode the datasheet proposes connecting REF1 and REF2 to GND, IN+ to the current "input" and IN- to current "output" (or: IN+ to the power supply and IN- to the load). What would happen if I swap the IN+ and IN- so that IN- gets connected to power supply and IN+ to the load and reference REF1 and REF2 to GND for unidirectional mode?

Thanks.

Kind regards,

Gabrijel

  • Hi Gabrijel,

    don't know whether I understand you correctly, but as the INA253 works like a differential amplifier, swapping the inputs would result in a negative differential input voltage causing the output also to go negative in respect to the potential of REF1 and REF2, which is GND. But because the output voltage cannot go more negative than the potential at the GND pin, which is GND, the output would go into saturation and emit some tens of mV and would hang there as long as the shunt current is flowing from IN- to IN+.

    Kai 

  • Hi Kai,

    yes, you understand correctly. My PCB layout would be better if used in the way I have described. OK, so my options are:

    1. use bidirectional configuration with mid-supply voltage having in mind that measured current will always be lower than set mid-supply point

    2. connect REF1 and REF2 to VS and that will result in having output=VS when 0A and less than VS when there is current flowing. This is even better than option 1. because I have full range for current measurement.

    Gabrijel

  • Hi Gabrijel,

    yes, you can do so. But please keep in mind that the output voltage can go closer to GND than to VCC. According to section 7.5 of datasheet the maximum output voltage you can achieve is VCC - 0.2V (worst case with RL=10k) while the minimum output voltage goes down to GND + 10mV (worst case with RL=10k). So you would lose up to 200mV output voltage swing where the output voltage would not react to input current changes.

    Kai

  • Hi Kai,

    thanks a lot for your help.

    Gabrijel

  • Hi Gabrijel,

    Thanks for the question and using the E2E forum!

    Kai is correct, you can connect both REF pins to Vcc and use the device to measure your current. Like he points out, you'll just need to be aware that the output can't quite get up to Vcc due to output drive capabilities, which means you won't be able to accurately measure smaller currents. The INA253 can typically drive to 50mV below Vcc, but could be as far as 200mV below Vcc (see data sheet snip).

    As long as your lower currents aren't as important as your larger currents, this configuration sounds like it's your best option.

    Louis