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INA240: output noise

Part Number: INA240

I'm using INA240A2 (50 V/V gain) for measuring current on 4 x 0,5 mOhm paralleled resistors (total 0,125 mOhm).

There is a noise at output of INA240 about 10mV (picture attached).

Power source 3.3V LDO TPS7A1601Q. Reference voltage 2.5V (LM4050).

INA240 output is directly connected to analog input of MSP432P401.

Noise is always the same independent of input (tried current from 0 to 40A)

I tried to disconnect and to shorten input – no effect.

Adding bypass capacitors up to 2.2uF to VS and REF1 pins – no effect.

Adding load resistors on output 1k to 20kOhms – no effect.

Cutting trace close to output pin – no effect (the same noise, INA is not connected to ADC).

I tried to supply circuit from battery and from DC power supply – no difference.

INA240 is about 5cm away from MCU.

3.3V supply for INA240 trace length is about 5cm, width – 0.5mm.

I soldered wire on PCB for 3.3V to INA – no effect.

Changing Vref to 3V3 – no effect.

I tested other board and noise is the same.

What can cause such big noise? Power supply, tracing, bad INA?

How to solve it?


  • Hello MMrobot,

    Thanks for considering to use TI. The noise you are seeing is actually not far off from the typical. If you take our specification of 40nV/sqrt(Hz) and multiply it by the sqrt(400kHz), you will get 25.3uV. This corresponds to the rms value at the input. The output rms value would then be 1.3mV. To get the peak to peak value we multiple the standard deviation (rms) by 6 as it is a non-deterministic signal. This yields a value of 7.6mV, which is only a little better than what you measured.

    To improve your noise situation you can use a low pass filter on the output, average more samples in your microcontroller, or you could perhaps increase your shunt value and use the A1 gain variant of the INA240.