TLC4502: Need replacemet for this part

I forgot to mention, it´s intended to be used in a PH meter input circuit

Hello Javier,

Please see the OPA2325, OPA2335 and LMP2022 datasheets:

www.ti.com/.../opa2325.pdf

www.ti.com/.../opa2335.pdf

www.ti.com/.../lmp2022.pdf

Regards, Thomas
Precision Amplifiers Applications Engineering

Hi Javier,

I expect that low input bias current (Ib) of the TLC4502 is important in the pH meter application. Its Ib is specified as 1 pA typical, 60 pA maximum at 25°C. The full temperature range Ib is 500 pA maximum.

Of the three precision op amps I suggested the OPA2325 has the lowest Ib. It is rated as +/-0.2 pA typical, +/-10 pA maximum at 25°C, and 500 pA maximum, over TA = –40°C to +85°C.

Regards, Thomas
Precision Amplifiers Applications Engineering

Hello Thomas, thanks for your reply!.

Excellent I´m going to look for this part. I was also looking the LMP7721 but it comes in single OP amp not dual.

What about OPA2316 and 2320 are they good candidates as well?

One more question, is there any reference design for this particular application of PH meter.

Thanks again.
Javier.

Hi Javier,

The OPA320 offers similar dc performances to the OPA325, but with higher bandwidth and slew rate. You probably don't need that in a pH application. The OPA316 is a very good, general purpose op amp so the voltage offset and voltage offset drift will be higher than that achieved with a more precision op amp. Its 25°C Ib is ±5 pA typical, and ±15 pA maximum.

I am not finding a specific pH meter reference design, but TI does have an AFE product that is intended for pH measurement applications. The product isn't from the Precision Amplifiers group that I am part of so I don't know a great deal about it. You can find its datasheet here:

www.ti.com/.../lmp91200.pdf

Regards, Thomas
Precision Amplifiers Applications Engineering