LM10: Differential amplifier followed by 2X gain amplifier

Walter Cromer

Part Number: LM10
Other Parts Discussed in Thread: TLV9002, TLV9052, TLV9062, DIP-ADAPTER-EVM

I am using the LM10 as a simple differential amplifier. Each input is attached to a copper probe that is essentially 'floating' electrically in a fluid. I am measuring the potential between the two copper probes with this circuit. It works beautifully. The LM10 is optimal because my output cannot exceed 1.8V or I blow out the ADC of the BeagleBone Black MCU we are using. (1.8 V zener's are out of stock EVERYWHERE.) So I power the LM10s with 1.8VDC. The output of the differential amp feeds into a simple non-inverting op amp with 2X gain using an LM10, again powered by 1.8VDC.

Our issue is 60Hz noise on the signal which is not present on our power supply. (The supply voltage rejection is pretty good on these units so I also question if that's where the noise is coming from. Granted this is all on a breadboard currently, no twisted pair or shielding, etc. Sort of a perfect situation for noise that we will address with a PCB and better connections.

My question however has to do with what do we need to do with pins 8, 1 and 5 on these op amps? We are not using the built-in reference voltages at all. Currently these are all floating. Should they be connected to something and if so, what? Could they introduce some noise?

Thanks!

Walter

over 3 years ago

0 Ron Michallick over 3 years ago

TI__Guru**** 164876 points

Hello Walter,

Pin 5 can be left open. Connect pins 1 and 8 together. The 60Hz noise probably comes for the air. The AC line frequency may be 60Hz in your region.

0 Walter Cromer over 3 years ago in reply to Ron Michallick

Intellectual 265 points

Thanks. I will do this and once confirmed everything is still working I will mark this as resolved. Quick question, I'm going to use the SOIC package on our PCB. So I should connect pins 12 & 3 on that package and leave 9 open, right?

0 Ron Michallick over 3 years ago in reply to Walter Cromer

TI__Guru**** 164876 points

Walter,

That is correct.

If the reference is not needed, then why not use a dual 1.8V op amp such as TLV9002 in a smaller (less pin) SOIC package?

0 Walter Cromer over 3 years ago in reply to Ron Michallick

Intellectual 265 points

I will look in to the TLV9002. We just happened to have some LM10's in stock in both through-hole and SOIC. And it worked. But smaller is definitely better!

0 Walter Cromer over 3 years ago in reply to Walter Cromer

Intellectual 265 points

The TLV9002 definitely appears to be a good option. However, we don't have the capability to work with a part that is this small in our lab right now. (We are a startup.) When we get closer to our first production models we could switch to it. I changed out several cables to add shielding on the input signals and cleaned up some other connections. The 60Hz noise is gone. Now we have some minuscule, manageable noise in the 72kHz range that we can live with. I connected 8 & 1 and left 5 open and all works as expected.

Thank you for your prompt help and suggestions!

0 Ron Michallick over 3 years ago in reply to Walter Cromer

TI__Guru**** 164876 points

Walter,

These EVM adapter boards make it easy to test smaller packages on 0.1" based breadboards.

https://www.ti.com/product/DIP-ADAPTER-EVM/part-details/DIP-ADAPTER-EVM

0 Walter Cromer over 3 years ago in reply to Ron Michallick

Intellectual 265 points

I'm ordering one of these adapter boards. That's cool! However, I can't find any TLV9002 in any package or form in stock using TrustedParts.com! Oh well.

0 Caro Walter over 3 years ago in reply to Walter Cromer

TI__Mastermind 22122 points

Hey Walter,

Is there a reason to not order from ti.com? There appears to be plenty of inventory: https://www.ti.com/product/TLV9002?keyMatch=TLV9002&tisearch=search-everything&usecase=GPN&login-check=true#order-quality

All the best,
Carolina

0 Walter Cromer over 3 years ago in reply to Caro Walter

Intellectual 265 points

Carolina,

I only see one version that has any stock on TI.com and we cannot work with that package in our lab. (We are a startup with limited resources currently.) I don't this the package that is available works with the DIP-ADAPTOR-EVM. If you can provide me with an adaptor part number that will work with the package that is available on Ti.com, I will gladly order it. Or, point me to a version available on line that has a DIP adaptor. I don't have an issue ordering directly from TI. I can take samples too!!!

0 Caro Walter over 3 years ago in reply to Walter Cromer

TI__Mastermind 22122 points

Hey Walter,

I am seeing the biggest package the TLV9002 comes in D (SOIC | 8) currently in stock:

This package is compatible with https://www.ti.com/product/DIP-ADAPTER-EVM/part-details/DIP-ADAPTER-EVM

I believe the above option is the best resolution; however, here are the details for the rest of the inventory:

The remainder of the packages I see in-stock may be covered by this EVM: https://www.ti.com/tool/SMALL-AMP-DIP-EVM

All the best,
Carolina

0 Walter Cromer over 3 years ago in reply to Caro Walter

Intellectual 265 points

I was out of the office yesterday so I may have missed the chance to order these while they were in stock. This morning, this is what I see.

Could it be that you have access to a different stock? Can you have samples supplied to me?

Walter

0 Caro Walter over 3 years ago in reply to Walter Cromer

TI__Mastermind 22122 points

Hey Walter,

I believe this is the best path forward: https://www.ti.com/info/strategic-relationships-and-ventures.html

Although, that might take some time...

I know that Ron recommended the TLV9002 but the TLV9052 and TLV9062 are very similar with some bandwidth differences. Here is the comparison table: https://www.ti.com/assets/js/compareParts/compare.html?familyId=1562&parts=TLV9062,TLV9052,TLV9002&cols=o1,p3318,p1130,p480,p1261max,p1261min,p78,p23typ,p22typ,p2954,p2max,p1typ,p7typ,p1498,p1192,p3316,p1811&lang=en

The quickest would be to buy from mouser, the TLV9052: https://www.mouser.com/ProductDetail/Texas-Instruments/TLV9052IDR?qs=qSfuJ%252Bfl%2Fd40FZ%252BJUm2hDA%3D%3D

All the best,
Carolina

0 Walter Cromer over 3 years ago in reply to Caro Walter

Intellectual 265 points

The bandwidth is not an issue for us in this case. We were going to use an LM10 originally and it works fine. I think the TLV9052 looks like a good alternative to the TLV9002. I'll try sourcing that one! Thank you so much for your help!

0 Walter Cromer over 3 years ago in reply to Walter Cromer

Intellectual 265 points

Well, it appears that the package that works with the DIP-ADAPTOR-EVM that I have already purchased is out of stock for the TLV9052 and TLV9062. I have no hair left. Any ideas?

0 Walter Cromer over 3 years ago in reply to Walter Cromer

Intellectual 265 points

I found the TLV9052IDR at Mouser and bought them. They are SOIC-8 so should be compatible with the DIP-ADAPTER-EVM product. Yeah! I also found 6 TLV9002QDGKRQ1 at Mouser and bought them too. They are the DGK VSSOP-8 package which is also compatible with the adapter board. I sure hope I can do these by hand so we can validate them in the design and then get the board ordered.

0 Walter Cromer over 3 years ago in reply to Walter Cromer

Intellectual 265 points

So for the benefit of anyone who might come along and read this seeking help... I received the TLV9052IDR (SOIC-8 package) and it was very easy to solder the SOIC-8 to DIP adaptor on the DIP-ADAPTOR-EVM product suggested above. I did this by hand with a small pen-point soldering tip. And I am not a spring chicken so my eyesight is not what it once was.

0 Walter Cromer over 3 years ago in reply to Walter Cromer

Intellectual 265 points

The TLV9052IDR that I received from Digi-Key does not have the pin 1 markings shown in TI's documentation. It has the TI logo. It has a bar across the chip so I assume that's the end pin 1 is on. But when I hooked it up, it did not work. Now, I could have blown something out, hooking it up. Could I get confirmation of what pin 1 is when the package doesn't have the dot and has the bar instead?

0 Caro Walter over 3 years ago in reply to Walter Cromer

TI__Mastermind 22122 points

Hey Walter,

I have drawn the bar in blue:

Additionally here is the pinout of the dip adaptor board:

And as I am sure you know, please have all "live" signals off while installing the device to not damage it.

All the best,
Carolina

0 Walter Cromer over 3 years ago in reply to Walter Cromer

Intellectual 265 points

Thanks. This confirms what I had assumed. I definitely connect it without any power applied. I'm installing a second chip to validate the circuit now. I expect it to work.

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LM10: Differential amplifier followed by 2X gain amplifier