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Original question:

OPA2192: unused pins

OPA2192: how to configure unused channel

Shinichi Inoue
Guru 20726 points
Part Number: OPA2192

Dear Specialists,

My customer read the attached application note (SBOA204A) on how to properly dispose of unused pins.

https://www.ti.com/lit/an/sboa204a/sboa204a.pdf

My customer uses different connection shown in Figure 2. Figure 3.

1) Connect the non-inverting/inverting input to GND and let the output pin float

2) Connect non-inverting/inverting input/output pins to GND

Regarding 1), there was a comment in the application note.

https://e2e.ti.com/blogs_/archives/b/thesignal/posts/the-unused-op-amp-what-to-do

Connecting both inputs to the same node will saturate the output and increase current consumption.

What kind of impact is possible regarding 2)?

Is it possible to think of output saturation and current consumption as in 1)?

Could you please let me know any other effects.

I appreciate your great help in advance.

Best regards,

Shinichi

  • +1
    Guru 287370 points

    Without negative feedback, the opamp works as a comparator. When connecting both inputs to the same voltage, the output state is determined by the offset voltage, which is random. So the output might saturate high or low.

    When a high output is shorted to ground, the current consumption increases even more (see figure 44). Shorting one output to ground is allowed by the absolute maximum ratings, so the device will not be immediately damaged.

  • +1
    TI__Guru 64530 points

    Unused op amp channels should be configured in such a way that the input common-mode and output voltage do NOT violate their linear voltage range as defined, respectively, in the condition column of datasheet CMRR and AOl specifications. https://e2e.ti.com/blogs_/archives/b/thesignal/posts/the-unused-op-amp-what-to-do

    Saturating the bipolar transistor output may greatly increase the quiescent current due to beta of the transistor falling down to 1 for VCE below Vsat voltage BUT since OPA2192 uses only CMOS transistors the negative side effect may be limited to only to somewhat shortened expected life of the product (not to any significant degree). 

  • 0 in reply to Marek Lis
    Guru 20726 points

    Hi Clemens and Marek,

    Thank you for your reply and teaching.

    I understand unused op amp should be configured in input common-mode range and output voltage range. 

    It should be It is necessary to use with the input signal to an appropriate level and a buffer circuit to prevent the output from saturating.

    I'll share these information(comment, application note and e2e blog) with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi