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OPA2277: Different VOUT distribution for 0V Input

Rocky Chen
Expert 8810 points
Part Number: OPA2277

Tool/software:

Hi Team

Customer Siemens used below OPA2277 circuit. (Rf/R839 = R1/R838 = 6.19Kohm)

They have been using below test way to decide if it the IC/functions well in their production line:

  • Input 0V to PIN5
  • Measure Vout (TP451)
  • They expected Vout should be within 1V
  • Actually, in previous material shipped, OPA2277 did performed like this, means Vout within 1V for 0V VIN.

But recently, for their new ordered materials, they found, in total 69 pcs devices, there are:

  • 28 pcs shows Vout within 1V range [38mV to 1V] for 0V VIN
  • 41 pcs shows Vout in range of [1V and 2.3V] for 0V VIN

Therefore, they wonder if there is any change happened on OPA2277 manufacturing. (There seems to be a PCN happened) 

For questions:

1) If above testing way make sense? Is the 0V input already violated the spec. of input range? [V- + 2 to V+ - 2] 

2) Why the newest 69 pcs shown different Vout distributions? Which IC spec. impact this?

3) I think there is some modification required for this circuit. As VOUT for the load of FAN_POT would be starting to work on 2V voltage. But currently circuit seems not able to be guarantee min. output at 2V, unless they change circuit to a Follower. Then VIN 2V can output VOUT 2V, without violation. Is this understanding correctly?

Thanks!

Regards

Rocky

  • 0
    TI__Guru* 76301 points

    Hi Rocky, 

    Rocky Chen said:
    Therefore, they wonder if there is any change happened on OPA2277 manufacturing. (There seems to be a PCN happened) 

    Yes, there was a PCN issued in OPA2277, where the GBW parameter has changed. 

    Rocky Chen said:
    1) If above testing way make sense? Is the 0V input already violated the spec. of input range? [V- + 2 to V+ - 2] 

    Yes, you are correct. The input Vcm range is 2V above Vee or V-, so the test condition at 0Vdc has no meaning (outside of the op amp's linear operating range). 

    Rocky Chen said:
    2) Why the newest 69 pcs shown different Vout distributions? Which IC spec. impact this?

    You need to test the op amp within the recommended input Vcm range. The post PCN OPA2277 IC has the same requirements, however, there may be different non-linear behaviors in post-PCN vs. pre-PCN products. In the linear operating range, two should be nearly identical. 

    Rocky Chen said:
    3) I think there is some modification required for this circuit. As VOUT for the load of FAN_POT would be starting to work on 2V voltage. But currently circuit seems not able to be guarantee min. output at 2V, unless they change circuit to a Follower.

    Could you send the OPA2277 image over and we can verify the post-PCN production? The simulation below is the still pre-PCN OPA2277's behavior, but the input has to be operated in a linear region. 

    Please let me know what is supply rail for the OPA2277 application and the BW requirements (seems to be low). We may need to do some circuit modification per the customer's requirements. 

    OPA277 PCN 07282025.TSC

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    TI__Expert 8810 points

    Hi Raymond

    Here is top side marking.

  • 0 in reply to Rocky Chen
    TI__Expert 8810 points

    Supply is 24V and 0V, no requirement for BW.

    VIN min will be as low as 0V ideally, it comes from a DAC. 

    Would be any other better p2p solution can be introduced? Dual channel, SOIC-8.

  • 0 in reply to Rocky Chen
    TI__Guru* 76301 points

    Hi Rocky, 

    The image is shown that this is post-PCN OPA2277UA op amp, A grade (U is a better grade). 

    The post-PCN has a wider GBW than pre-PCN, shown below. The datasheet has not been updated. 

    Rocky Chen said:
    Actually, in previous material shipped, OPA2277 did performed like this, means Vout within 1V for 0V VIN.
    Rocky Chen said:
    Supply is 24V and 0V, no requirement for BW.

    TI does not guarantee the non-linear operating behavior. In this case, Vin=0V violates the input Vcm range, and the op amp is operating in non-linear mode. The minimum input Vcm is 2V above GND, and Vout can not be guarantee to be within 1V if the input Vcm does not meet the linear input Vcm range. And the best option is to change the op amp or change the input Vcm range. 

    If you have other questions, please let me know. 

    Best,

    Raymond