OPA2192: Design query regarding OpAmp unused pins

Nitesh Bhurke

Part Number: OPA2192

Hello,

We are using 'OPA2192IDGKT' in one of our design. The opamp has 2 opamp circuits in one IC package. As per our requirement we are using only one opamp circuit. So can we keep the pins belonging to other circuit floating? or it should be grounded.

Regards,

Nitesh

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 318050 points

Neither floating nor grounded (with a single supply). See e2e.ti.com/blogs_/archives/b/thesignal/posts/the-unused-op-amp-what-to-do. In general, you should configure the unused opamp as a simple voltage follower with a voltage somewhere between the supplies.

Consider whether you can use a G=1 buffer somewhere in your circuit; increasing the input impedance or decreasing the output impedance of some signal is often useful.

0 Nitesh Bhurke over 1 year ago in reply to Clemens Ladisch

Intellectual 260 points

Thanks for the reply and shared article. We are using single supply (5V). I have attached image of our design. As per the new requirement of design, the components connected to U11B are not needed. (The section not required) so we are making them DNP (Do Not Populate). As we can not keep the unused pins of opamp floating. Can we go with the configuration of R59 mounted (0 OHM) for negative feedback, and R399 and R58 replaced with 0 OHM to connect non-inverting terminal of OPamp to GND? And remaining component will be DNP. It seems difficult to connect non inverting terminal to Vref as per our design. So please provide the response for the same.

0 Clemens Ladisch over 1 year ago in reply to Nitesh Bhurke

Guru 318050 points

R59 is OK.

What is the signal at the left of R56? Or can't you add a 0 Ω connection to U11A's input?

When you connect the input to 0 V, then the opamp tries to drive its output to 0 V. If the input has a negative offset voltage, then the output will try to drive below GND, which is not possible and will overload the output. This will not damage the device (see section 8.3.8) but might increase the power consumption.

0 Art Kay over 1 year ago in reply to Nitesh Bhurke

TI__Mastermind 25488 points

Nitesh, Just letting you know that I agree with Clemens excellent support.

Best regards, Art

0 Nitesh Bhurke over 1 year ago in reply to Clemens Ladisch

Intellectual 260 points

Hello Clemens, Thanks for the reply and explanation.

The signal left of R56 is 0-10V. But as per the new requirements we are not using this (0-10V) input path. Hence we are making all components in 0-10v path as DNP. There is one MUX before R56 which selects between the 0-10V input path and 4-20mA crrrent path flowing through R50, U11A path.

Can you please elaborate the point regarding '0ohm connection to U11A's input'?

+1 Art Kay over 1 year ago in reply to Nitesh Bhurke

TI__Mastermind 25488 points

Nitesh,

If you short the input to GND, the device may draw more IQ. Thus, it is better to apply a voltage to the input of unused devices to keep them in a linear state. It should not be a significant problem if you ground the input but it is better to apply a voltage the keeps the amplifier in a linear state.

Best regards, Art

+1 Clemens Ladisch over 1 year ago in reply to Nitesh Bhurke

Guru 318050 points

Make a connection to some node with a valid voltage. The 0 Ω allows you to break the connection if you want to actually use the second opamp.

0 Nitesh Bhurke over 1 year ago in reply to Art Kay

Intellectual 260 points

Hello Art, thanks for the valuable support.

0 Nitesh Bhurke over 1 year ago in reply to Clemens Ladisch

Intellectual 260 points

Hello Clemens, thanks for the valuable support.

0 Nitesh Bhurke over 1 year ago in reply to Clemens Ladisch

Intellectual 260 points

Hi Clemens, is it ok if we connect the pin 5 of U11B (non- inverting input) to 5V.

Note: Supply voltage of Opamp is 5V.

0 Clemens Ladisch over 1 year ago in reply to Nitesh Bhurke

Guru 318050 points

It would have the same problem as 0 V.

(Both 0 V and 5 V are allowed; the worst that can happen is increased power consumption.)

0 Nitesh Bhurke over 1 year ago in reply to Clemens Ladisch

Intellectual 260 points

Ok, understood. So the voltage at the input pin should be between 0 to 5V. Right?

0 Clemens Ladisch over 1 year ago in reply to Nitesh Bhurke

Guru 318050 points

Yes (if possible).

0 Nitesh Bhurke over 1 year ago in reply to Clemens Ladisch

Intellectual 260 points

Thank you, Clemens

0 Nitesh Bhurke over 1 year ago in reply to Clemens Ladisch

Intellectual 260 points

Hello Clemens,

Due to layout limitations we cannot add new component/ connection in design. So we are searching for the single circuit opamp IC with the pin mapping as per the attached image below to eliminate the unused opamp, I tried, but I did not find the suitable opamp.

Can you please check if you are able to find any such opamp?

Note: The package should be 8 pin VSSOP/ SOIC.

0 Nitesh Bhurke over 1 year ago in reply to Clemens Ladisch

Intellectual 260 points

Hello Art,

Can you please check if you are able to find any such opamp?

Note: The package should be 8 pin VSSOP/ SOIC.

0 Clemens Ladisch over 1 year ago in reply to Nitesh Bhurke

Guru 318050 points

There is no such device; all 8-pin single-channel ICs use a different, standard pinout:

If you do not want to add an adapter board, then your only choice is to use a dual opamp, and to live with the additional power consumption. (It might not be too bad. Or you could select chips with a positive offset voltage.)