TLV2231 output at rail

Hi Emmett,

The TLV2231 is usable with +/-5 V dual supplies so that shouldn't be an issue. I don't find any problem with your schematic and would expect to see about -0.05 V at the pin 4 output, with the same voltage at the pin 1 input in a normally functioning circuit.

Having the output locked at +5 V tends to suggest some kind of connection, contact, or another unexpected issue. Here are some things to check:

• How many TLV2231 devices have been checked in the circuit? If more than one, do they all lock up?
• Is this a prototype circuit?
• What kind of assembly was used for this TLV2231 circuit?
• If a PC board is being used, does its TLV2231 pad arrangement conform with the DBV package top view shown at the top of datasheet Pg. 1?
• If you have an O-scope check the output for oscillation, or other condition. Is it clean, but just up against the positive rail?
• Was the TLV2231 obtained from a authorized TI distributor?

Let me know what you determine and we'll go from there.

Regards, Thomas

PA - Linear Applications Engineering

Hi Thomas,

Thanks for the reply.

I have tried 2 devices with same results.

This is a prototype, on a production-quality PCB.

The footprint is good, have used it many times, even with this device.

I don't see any oscillations with an oscope.

Yes we bought these from Digikey probably, and use them in other products.

Right now I am running it no-load. I notice that the output drops a little if I load it with 1KOhm,

I didn't see a minimum load spec, is there one?

Thanks, Emmett

Hi Emmett,

When operating correctly the TLV2231 output voltage should be very close to the same value regardless if the load is an open circuit, 1 Megohm, or 600 Ohms, because it is a closed-loop control circuit. That would be the -0.05 V level you expect.

If the output is up against the positive rail and a heavier load is added such that the output is sourcing higher current, then the output will move away from the rail a little. But note in this condition the op amp is operating in saturation, not its linear range, and all of the loop control is lost.

Do you have some other TLV2231 devices from an earlier time that you are confident are good? If so, you might try one of those in your circuit. If you don't have any, you can order some free samples through the TI website and try them. Hopefully they would be from a different production run/ date code than the ones you are currently finding problems.

Regards, Thomas

PA - Linear Applications Engineering

I used the wrong pinout! (from TL271)

Thanks for your help,

Emmett

Hi Emmett,

Op amps in the SOT-23 package pretty much come in one of two pin out plans. So when selecting a different amplifier that comes in that package it is an easy thing to automatically use the pin out you are used to. I've had to train myself to check that up front.

I am glad you found the problem. I hope the TLV2231 does a good job for you.

Regards, Thomas

PA - Linear Applications Engineering