INA168: Common Mode voltage not more than 60V

Hi Prashant,

how much error does your application allow?

Kai

Hello Prashant,

Thanks for coming to TI for your current sensing solution.

What is the maximum possible current you need to measure? This will limit your shunt resistor size, which will limit the error on the low end of current range (15A). Which technique/solution to increase common mode are you referring to? Here are some options.

TIDA-00313: INA226 (Zener powered) + ISO1541
- This will provide most likely the best error since maximum input offset voltage (Vos) is +-10uV.
- Digital I2C output

TIDA-01608: INA260 (ISO powered) + ISOW7842
- For your case, you cannot use the INA260 because it has internal shunt resistor that can't accept more than 15A of continuous current, but this design shows how to use another high-voltage I2C isolator with one of our digital current sensing devices.
- Most of error will come from the INA260 (or whatever digital current sense amplifier is chosen).
- Digital I2C output

TIDA-00528: INA226 (MCU powered) + OPA333 (Zener powered) + Transistor
- This approach uses a precision operation amplifier to sense the current and level shift the sense current so INA226 can read and report it directly to MCU I2C bus.
- This approach will allow you to use a voltage-output current sensor (IN181 for example). You are not limited to the digital output devices here.
- The error here seems to be slightly higher compared to previous two designs since more analog components are needed.

TIDA-00332: INA138 (Zener powered) + Transistor
- This takes advantage of using our current-output amplifier and level-shifting the output using a transistor.
- Will have the highest error since INA138 has higher input offset votlages (Vos max = +-1mV) and gain error. The load resistor tolerance will also add error.

AMC1200/AMC1100
- These current sensor device includes the isolation barrier internally so minimal components needed.
- Has large offset comparitively (+-1.5mV Vos max), so this will be main contributor of error.

INA149-EP
- This is a difference amplifier with maximum 500V allowable common-mode.
- Has a 3.5mV Vos max, so this will be main contributor of error.

Hope this helps.

Sincerely,
Peter Iliya
Current Sensing Applications

Hi Kai,

I came across following sentences to increase CMV ,

The high common-mode range of the INAXXX is achieved by dividing down the input signal with a high precision resistor divider. This resistor divider brings both the positive input and the negative input within the input range of the internal operational amplifier, but again voltage divider has serious consequences with output error and result degradation in system performance. 

My application allow max Gain error = +/- 0.1%

And Offset Max 10uV 

In addition , I have attached Block dig. of Application , Please go through it and suggest best option.

Thanks,

Prashant

Hi Peter,
Thanks for your valuable reply. I will select one of them but As i mentioned in above post you will get idea what exactly I want to do, So as of now i have selected INA149-EP.

But again you mentioned that it has got 3.5mV Vos. And my application has Rsense drop of around 75mV , According to my knowledge for mV diff. signal this Vos will dominate factor.

Another option for me is INA138 (Zener powered) + Transistor
CON's
-Will have the highest error(Offset and Load resistor)

So i confused between above option please refer best part of TI.
Thanks
Prashant

Hello Prashant,

In order to best help you I need to know the current range you are trying to measure: what are the maximum and minimum currents you need to measure. This is your dynamic range requirement and will limit how low of an error you can achieve. You will most always get the greatest error at the lowest current you need to measure.

Sincerely,
Peter Iliya