Which LDO is the AD8422 suitable for?

Hi yaro-0916,

Just to clarify a few things:

yaro-0916 said:

(1.) I already have the ADR4550 as a reference voltage do I still need an LDO?

With this statement, do you intend to use the LDO as supplies for the InAmp?

yaro-0916 said:

Excuse me, how do I generate +-5V to power the AD8422 instrumentation amplifier?Is it to use two LDOs

Do you plan on using the supply you used for the reference amplifier and use an LDO to get the +-5V supply? If you only have one supply (+5V) this would be the best way to power up the amplifier. 

yaro-0916 said:

By the way, my signal V+ is 2.2V, V- is 1.4V, after 10 times the output is +-4V?

When you say after 10 times, do you mean you have a gain of 10?

Regards,

Kristine

Sorry, English is not my first language, google translate may be wrong.

(Q1.)With this statement, do you intend to use the LDO as supplies for the InAmp?

(A1.)I already have an ADR4550 voltage reference. I'm not sure if it's possible to power an in-amp directly with the ADR4550? Or I have to connect an LDO after the ADR4550 voltage reference. figure 1. ).

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（Q2。）Do you plan on using the supply you used for the reference amplifier and use an LDO to get the +-5V supply? If you only have one supply (+5V) this would be the best way to power up the amplifier. 

(A2.)I'm using a differential mode ADC and I want the in-amp to output a +-5V acceleration signal. (Picture 2.) So I'm not sure how to properly generate +-5V to power Vin+ and Vin- of the InAmp. (image 3.Is this correct?)

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(Q3.)When you say after 10 times, do you mean you have a gain of 10?

(A3.)sorry it was a translation error, i meant gain=10

Hi yaro-0916,

Thank you for the clarification!

ADR4550 only outputs +5V. If your region of operation would be +/-5V, yes you would need an LDO to supply the -5V. You can consult the Power Management Community for the best generic for this application.

To obtain a +/-5V output, refer to the transfer function below:

For an output of 5Vpk, with 2.2V and 1.4V input, you can try to configure your gain to 6.25 as per the Vout transfer function. Based on the G formula, your Rg should be 3.7kOhm to have a gain of 6.25. Another thing to note is that is your ref is 5V, this would saturate your output. Try setting the ref to <2.5V and >-2.5V. Lastly, AD8422 has an output swing limitation of as seen below:

You should raise your supply rails to compensate the output swing of AD8422.

Hope this helps!

Kristine