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INA818: INA818ID

Part Number: INA818

Hello Dear Respected Sir/ Ma'am,

I am trying to use instrumentation amplifier with part number of INA 818ID to amplify and denoise the output of GMR current sensor. My sensor is able to generate max 400mV and its output impedance is 2.5kohm. Gain resistor that I am using with this IA is a 1kohm to generate voltage gain of 6. I have couple of questions about your product as:

1. Is this device suitable for the GMR sensor with the mentioned specifications?

2. When I am implementing small voltages around 20mV till 250mV directly to input of the IA, I am not getting gain of 6 always. In other words, according to the voltage I am giving as signal to IA, gain is not fixed. Is there any reason and solution for this problem? 

Please let me know if further information is needed to reply these questions.

Sincerely Yours,

Sama Salehi Vala

  • Sama,

    First, the INA818 gain equation is G=1*50k/Rg so for Rg=1k the gain would be 51 and not 6 - see below.  If you need gain of 6, you need to use Rg=10k.

    The input and output voltage linear range is a function of supply voltage (see below) but none is stated.

    Also, the linear range of input and output voltage is a function of the input common-mode voltage and reference voltage but you do not provide any such info - see below.

    Please download the TI engineering calculator by clicking on the link below and use Vcm vs Vout for Instrumentation Amplifier to determine INA818 valid input/output ranges for a given supply, reference and Vcm voltages.

    https://www.ti.com/tool/ANALOG-ENGINEER-CALC?keyMatch=INA%20CALCULATOR