INA827: Gain too high

James Klineflter

Part Number: INA827

I am attempting to use this instrumentation amplifier to amplify a DC signal that ranges from 0V to 114mV. This range does not give enough resolution for my data logger system. I built the circuit according to the typical application circuit and gave it a 5V supply voltage. A 16k resistor was used for Rg and I thought that it would give me a gain of 10.

At the input I measure 20mV and at the output I get 1.5V, which is a gain of 75.

If I remove the gain resistor, which should give me a gain of 5 the output then decreases to 1.3V.

I just need this chip to work like how it claims to work and I cant figure out what im doing wrong.

over 4 years ago

0 Raymond Zhang1 over 4 years ago

TI__Guru 61301 points

Hi James,

How do you connect the 20mV DC signal? INA827 is instrumentation amplifier, the input voltage has to be differential, see the attached simulation.

I think that the following circuit is what you had, except the input voltage. I placed 2V source to drive 2.02kOhm; it generates 19.8mV differential voltage across 20 Ohm resistor at input, the Vout =198.0mV, since G=10.

Please also watch for input common-mode voltage required for this part, see Figure 8 of the datasheet (for a single voltage supply rail).

If you have other issues, please let us know.

/cfs-file/__key/communityserver-discussions-components-files/14/INA827-E2E-06092020.TSC

Enclosed is a link of instrumentation amplifier for your reference.

http://www.ti.com/lit/an/sboa282/sboa282.pdf?ts=1591728367775&ref_url=http://www.ti.com/sitesearch/docs/universalsearch.tsp?searchTerm%3Dinstrumentation%20amplifier%20application%20notnote

Best,

Raymond

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INA827: Gain too high