LMP91200: pH sensor suggestion

Hi Team,

Any update on this?

Also, Are there any Eval board with LMP7721 with LMP7715

One more query,

Datasheet suggests, LMP7721 with LMP7715 combination:

But  AN-1852 Designing With pH Electrodes (Rev. A) suggests of Two LMP7721

Which one to be followed.

Can you please let us know the use case with LMP7715/14?

Are there any eval board similar to TIDA-00561

Thanks

Hi Ren

For accurate sensing of pH Sensor which one would you suggest?

LMP91200 based solution or LMP7721 & LMP7715 series combination?

Thanks

Hello LKN,

For ambient temperature LMP7721 input current looks better, for highest temperature, LMP91200.

Hi Ron

Which one do you recommend? over LMP91200 & LMP7721+LMP7715 for accurate pH sensing (Accuracy changed to 0.01 min)

Are there any eval-board for LMP7721 and LMP7715 combination?

Since we want to test using dev kit first

KLN,

There is this LMP7721 only eval board here: https://www.digikey.com/en/products/detail/texas-instruments/LMP7721MAEVALMF-NOPB/2513243

LMP7715 is the guard buffer, depending on far far way the sensor is, it may or may not be needed. 

KLN said:

pH sensor accuracy: ± 0.1 pH

What is this value in units of voltage?

Hi Ron Michallick 

So if the sensor is nearby we wouldn't need LMP7715?

Over these two LMP7721 vs LMP91200 which one would you recommend?

Hi  Ron Michallick /  Ren Schackmann

We are planning to use LMP91200

Eval board is not available for ordering. Can you suggest alternate?

Thanks

I also have another question on Tri-axial connection recommendation on App note

In my case, pH sensor is from Atlas-scientific with tinned lead wires.

How should I make Tri-axial connection? Any recommendation?

Thanks

KLN,

KLN said:

How should I make Tri-axial connection? Any recommendation?

I don't think you need one. You do want to guard "+" traces on the circuit board and remove solder mask over "+" trace

KLN said:

We are planning to use LMP91200

Eval board is not available for ordering. Can you suggest alternate?

I have no alternative. 

Hi  Ron Michallick /  Ren Schackmann

This kind of guarding layout is not required?

Any other Evaluation board for LMP91200?

Any future plans for LMP91200 Eval board availability?

Currently It is very difficult to get Eval board for this.

This Eval Board is available for order?

Thanks.

Can we use LMP91000 Eval board in place of LMP91200

Where can I buy this below board?

KLN said:

This kind of guarding layout is not required?

This kind is highly recommended.  I couldn't find a place to order it.

I'll transfer post back yo LMP91xxx  test

Hi Alex

Thanks for your reply.

I'm using LMP91200 with MCP3421 for pH application.

where in MCP3421 has internal reference voltage of 2.048V

I've few questions on LMP91200 Reference voltage,

In TIDA-00561 Reference voltage is 2.048 using REF3220.

  Can I use 3.3V as reference voltage for LMP32100?

  If I use 3.3V as reference voltage VCM=3.3/2=1.65

For pH 0=434mV Output of LMP91200 will be 1.65+0.434V= 2.06V which is close to Max reference voltage of MCP3421, Will this be an issue? Is my understanding correct

Can I share PCB Layout for review.