# INA199: INA199

Hi Sir,

My customer using INA199C, we read voltage of ADC, the value very close real voltage (difference around 0.1V)

But if check current of ADC, it difference around 20mA~300mA with real current, is it acceptable?

Thanks, Ian.

### 4 Replies

• Hello Ian,

Thanks for reaching out on the forum. If your customer expects 20mA and they are measuring 300mA, that is unacceptable. To better assist you and figure out why their measurements are off I need the INA199 supply voltage, the shunt resistor value used, the common mode value at the INA199 input, the intended current measurement range, and the name of the ADC connected to the INA199.  Everything but the ADC info is needed for calculating the various error contributions.  The ADC may indicate whether the maximum capacitive load has been violated. I will also need to know the differential measurement between IN+ and IN- as well as the differential measurement between REF and OUT.  These values should be collected directly at the INA199 pins if possible rather than at a test point, which may not be properly placed.

If you are unfamiliar with the various error sources in current monitor and would like to get familiar with them, I recommend watching our tutorial videos found here.

Best Regards,

Patrick Simmons, TI Sensing Products Applications Support

Getting Started with Current Sensing Video Training Series

TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

• Hi Ian,

please post a schematic and some scope plots.

Kai

• In reply to kai klaas69:

Hi Sir,

The schematic as below,

We read ADC(1412) calculate I-MOND(0.965V) and measure value is I-MON(0.97V); looks make sense.

But measure current is 2.12A, calculate to I-MON (0.848V) looks not make sense

Condition:

R609= 2m ohm

R601=4.7K

Thanks, Ian.

• In reply to Ian Wang:

Hello Ian,

For 2.12A across a 2 mohm measured by a 200V/V gain INA199, I would expect 0.848V output.  If I interpret you correctly, you're not measuring that number on your ADC.  If you disconnect the ADC from the INA199 output and are able to measure 0.848V with a multimeter, then I think you might need to buffer the INA199 output for the ADC.  If you disconnect the ADC and still cannot measure 0.848 from the INA199 output, then I would probe your V+ pin.  It could be that your 3.81V boost is not adequately designed to supply 2A, so when that much current is sourced the INA199 supply might be drooping below the minimum operating voltage.  Disconnect the ADC and probe the INA199 output and let me know what you observe.

Best Regards,

Patrick Simmons, TI Sensing Products Applications Support

Getting Started with Current Sensing Video Training Series

TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.