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Hello Sir,
Good Evening,
This is Eazhil Having some doubt with Current sensor INA139 SOT23-5. Previously i'm using INA271 SOIC Package for High side current sensor for my circuit, but i'm facing issues like board to board output voltage difference and output appearing with 0 A of current like tat. After that one of my colleague check with your Texas person and he has explained about the Offset voltage of the INA271 is very high, so there will be some issues with and the Accuracy is very low. later he has suggested INA282 part with low offset voltage. It is for higher voltage part.
But in my case I need a lower voltage part which is upto 36V, so i've selected INA139 which is 40V. Kindly please suggest me that whether i also will face the same issues because we'll monitor from 0.1A to 20A with little accuracy.I've checked with INA283 which is pretty good. But i need lower voltage with lower cost. So kindly please suggest some ideas regarding the selectoion of current sensor
Hello Eazhil,
I am not sure what you mean when you say you need lower voltage, but I'll assume you need a device that can accommodate a 36V common-mode voltage.
Determining the best device will require knowing the following:
- Power supply for current sensor
- Allowable full-scale output voltage
- Device frequency response needed (do you want to measure AC or DC current?)
- How low can common-mode voltage go?
- Allowable power dissipation with your shunt resistor
Anyway the input offsets (Vos) are relatively high for INA271 (0.5mV to 2.5mV) and INA139 (0.2mV to 1.5mV). So this will limit how small you can make your shunt resistor. It is difficult/impossible to have an output voltage of 0V for input sense current of 0A if part is referenced to ground and powered with single supply. All amplifiers work this way in that they can never truly be driven to ground. Additionally, the higher the Vos, the further the output's swing to ground is since the offset will be gained up by the device. You can read about swing to rail specifications here in our FAQ articles: e2e.ti.com/.../3579.understanding-swing-to-rail-specifications
Keep in mind 0.1A to 20A is large current range to measure. You will need to make sure that your minimum sense voltage (Vsense_min = 0.1A*Rshunt) is greater than device Vos_max. You will also need to ensure that device can drive your maximum sense voltage (20A*Rshunt).
For example let’s consider the INA139. Overall, you want your Vsense_minimum > Vos_max = 2.5mV. If Rshunt = 100mOhm, then for 0.1A to 20A, IOUT = 10uA to 2mA. The device might not be able to drive 2mA depending on what you load resistor and power supply is. Please see datasheet section below:
For the INA282 let’s consider Rshunt = 10mOhm. Then for 0.1A to 20A sense current, Vout = 50mV to 10V. This will only be possible if INA282 is powered with >=11V power source.
If you need to actually sense 0A current then you supply a reference to your current sense amplifier (CSA) (INA282 has a reference pin). Thus once current is actually 0A, then your output voltage will equal your reference voltage. If you need more information on how these products work, please see our training videos.
https://training.ti.com/getting-started-current-sense-amplifiers
Sincerely,
Peter Iliya
Current Sensing Applications
