TL084H: Input stage question and availability of new SOT-23-THN (DYY) package

It meant the OPA 810, sorry ...

Hey Mirko, 

I have re-assigned the thread to High Speed op amps to help with OPA810. 

As for TL084HIDYYR availability, may be available as early as October 2021 but is expected latest by mid-November 2021. 

All the best,
Carolina 

Hello Mirko,

   Are you looking for similar products like the OPA810 in terms of FET input and high differential input voltage? Are you not able to use the OPA810 in your application? We also have a line of comparators as a subsection to our amplifier portfolio that fit this type of application. 

   When an amplifier is fed a fast-moving input signal, the current into transistors reaches its maximum current which is when a differential voltage will start develop at the inputs of the amplifier, and the voltage at the miller capacitance will start to increase linearly. Comparators do not have this miller capacitor. 

   The input bias current vs differential input voltage can be found in the OPA810 datasheet in Figure 7-54. 

Thank you,

Sima 

My application is a +-10V multichannel multiplexed sampled system running at settling times of about 1us to 0.01% ... 0.001% depending on the voltage steps needed. 

The application of the OPA would be to operate as a voltage follower after a low gate charge multichannel multiplexer (e.g. MUX508).

The main problem is not settling time of the OPA itself (TL04H would meet this most likely), but charge injection imposed by the input protection circuitry of the follower OPA into the preceiding circuitry, which could increase overall settling time by a few hundred nanoseconds, thus further increasing the settling requirements for the OPA.

The OPA810/2810 can't be used for several reasons:

- It is way to costly (there are 40 OPAs in the application and OPA810 is 50x more costly than a TL08H per OPA)

- The application is battery operated and thus the supply current should be less than 1.5mA, 2mA worst case per amplifier.

- The maximum differential input voltage of +-7V is too low to be 100% safe in an +-10V environment

- Due to its clamping circuitry it still injects slightly pretty much charge at steps of 10V (>30pC).

The closest match from TI to the above requirements seems to be the TL084H and the OPA1644, while the latter is still a little bit too costly and input cap a little bit too highish.

If the TL084H had the input stage topology of the OPA1644 or OPA4141 or OPA2145 (Or competing parts like ADTL084 or AD713), everything would be fine, but if it has a MOS input stage with antiserial calamping J-FETs like the OPA810, due to its slow rise time it would inject easily 200pC, which would be way too much.

The TL08H is the fastest settling high voltage FET amlifier from TI with an Icc of 1mA or less and by far the cheapest .... A great product ...

So to make it 100% clear:

- Is there a clamping mechanism in TL084H (and other members of its family) to protect the input stage against large differential voltages or not ?

Hello Mirko,

   Thank you for the additional information! Also one more question, what are the input frequencies into the mux?

    And I agree, you would need to look at a higher differential voltage requirement which the TL084H's wide differential voltage range would meet. Amplifier input pins are almost always diode-clamped to the power supply rails. Differential clamp diodes are only present in some amplifiers. Here is a blog post we have detailing how differential input clamps would affect mux type applications. 

    I do not think with TL084H and its specified wide range of differential voltages would have this input diode protection circuitry. I will re-assign this thread to the team that covers this device, and they will be able to provide a confirmation shortly.

Thank you,

Sima 

Hey Mirko, 

It looks like TL084H has the same input technology of OPA2145: 

All the best,
Carolina