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I want to use the AD8230 instrumentation amplifier.

I have bought one and connected it like this:

enter image description here

The datasheet says that this will be gain of 2, so on the output (pin 8) I should have +1 V. Sadly, I have +2.8 V, even though I have increased the voltage value on pin 4 to +5 V.

What have I done wrong?

Ok, so according to the answers, I have connected the amplifier like that: The way of connecting after comments

I have calculated the gain from datasheet, and it should be something around 53. Now, on the output I have +11,8V. Am I right that the problem is, again, with the REF voltage? Should I put a +5V to the booth of the pins?

Felipe
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    I hope you have a good reason for using an instrumentation amplifier to get a gain of 2. A regular single-supply or RRIO op-amp will do a fine job with two external resistors and none of the issues you are seeing. – Spehro Pefhany Dec 21 '22 at 16:07
  • To be honest, I just want to test that op-amp. I want to use it with max, 1000 gain, but I want to be sure that I connected it properly. I don't have enough sensitive tools to measure it properly. – Felipe Dec 22 '22 at 08:49
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    Please check the common mode range – Hari Dec 22 '22 at 08:55
  • @Felipe A regular (single-supply or RRIO) precision op-amp will do fine at a gain of +1000 too, if you only need single-ended input. Instrumentation amplifiers should be reserved for when you need high impedance differential inputs. – Spehro Pefhany Dec 22 '22 at 09:10

1 Answers1

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You're operating the AD8230 far outside of its permissible output reference voltage range.

Table 1 in the datasheet gives the operating range of the reference voltage input: Reference input spec Restriction on reference voltage for G<10

This means that the amplifier will malfunction if you apply less than 4.24V to Vref in a single-supply circuit with G=2.

Additionally, at G=2, the output voltage range (with respect to Vref) is limited further: Output voltage range vs. common-mode input voltage

This means that you can only operate this amplifier at G=2 with Vref>=4.24V and a maximum output voltage of +/-600mV relative to Vref.

You can fix this quite easily by using symmetric supplies (i.e. +/-8V), but the +/-600mV output limitation will remain unless you use higher gain (>=10).

Jonathan S.
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  • Thank You, I have changed something, and it seems that I am closer to solution. Am I thinking right ,now? – Felipe Dec 22 '22 at 15:04
  • It really isn't going to work as long as the Ref inputs are outside of the permissible voltage range (the chip will malfunction). In any case, as already mentioned, a much simpler solution would be to just ditch the AD8230 and use a regular rail-to-rail OpAmp instead. If you bias the Ref inputs with +5V, the AD8230 should work, though. – Jonathan S. Dec 22 '22 at 15:55