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OPA564: IFLAG and TFLAG behavior

BGX561
Intellectual 610 points
Part Number: OPA564
Other Parts Discussed in Thread: TINA-TI, TMP411

TI,

I have constructed a circuit using the OPA564. Everything appears to be working fine, thus far --- but I am trying to validate the correct behavior of IFLAG and TFLAG.

First, for TFLAG I want to verify the correct behavior when used in conjunction with the E/S pin.

  • It appears that in my test circuit, TFLAG is high when E/S is pulled low (shutdown).
  • It is also high when E/S is high or unconnected, but has gone into thermal shutdown.

Thus, is it true that TFLAG is high whenever the device is shutdown?

Second, for IFLAG I want to verify that the correct behavior when in operation, with ILIM resistor 54.9k, ( Sets current to 24000/(54900+5000) = 0.40066778 A )

  • I cannot get the current to go over 0.300 A in the circuit when it is set in this way.
  • In the same scenario, I am seeing an immediate drop toward 0 A the higher and higher I try to push the current after this threshold.
  • I cannot trigger IFLAG for this reason.
  • It is variable however, if I use 20k in parallel with the 54.9k for example ~14.66k = 1.22A it falls off right around 1.05A.

How can I trigger IFLAG without it 'pinching off' right before the value?

Worth noting is that I am using a level shifting circuit on BOTH outputs. they are identical. for both IFLAG and TFLAG.

Vdig is +4.3V and VCC is +5V in this scenario. V- is -6V and V+ is +6V

Thanks

  • 0
    TI__Genius 11135 points
    BGX561

    Our power OPA person is out of the office until Monday. We'll get back to you at that time.

    Dennis
  • 0 in reply to Dennis Goeke
    Intellectual 610 points

    Got this figured out! 

    Looks like the issue I was observing was a combination of two issues. First, it seems I mislabeled IFLAG and TFLAG on my test PCB. This immediately cleared up the behavior I was seeing.

    To revise my previous question: 

    Is IFLAG always active when the E/S pin is pulled low?

    I was able to validate that the IFLAG works as expected at higher current limits. Using the resistor setup I described before it consistently triggers now.

    I was also able to validate that TFLAG works as expected as well, by running the OPA564 without a heatsink briefly at a high current.

    Insofar as my level shifting circuit, any feedback on how it might be improved? Any gotchas for using it with the OPA564? It appears to work fine in TI-TINA.

  • 0 in reply to BGX561
    TI__Guru* 93105 points

    Hi BGX561,

    Here's answers to your questions:

    Is IFLAG always active when the E/S pin is pulled low? When the E/S pin is pulled low the OPA564 goes into shutdown mode.

    Yes. When the OPA564 E/S pin is pulled low and the amplifier goes into shutdown mode the IFLAG is active high, even though the output is shutdown and unable to supply current.

    Insofar as my level shifting circuit, any feedback on how it might be improved?

    I tried setting up your level shift circuit in TINA and it doesn't seem to work for me. You can see the result below. If you provide the results you obtained from your simulation we can compare them.

    Any gotchas for using it with the OPA564? It appears to work fine in TI-TINA.

    I need to see your TINA-TI results.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Intellectual 610 points

    Thomas,

    Your input wave VG1 and Vdig are incorrectly referenced.

    Since in the OPA564 datasheet, Vdig is referenced to V-, not GND. Likewise,  VG1 should be referenced to V-, not GND.

    Try replacing the grounds attached to these sources with V- and it should function as expected.

    Cheers.

    On related note, is there a reference on how to read the temperature sensor (thermal diode) on the OPA564 without a TMP411?

  • 0 in reply to BGX561
    TI__Guru* 93105 points

    Hi BGX51,

    It looks like I didn't have enough information about the level shift circuit to set up the TINA-TI simulation as you had. Nonetheless, if you find it is doing what is needed it should work nicely with the OPA564 flag circuits.

    The TSENSE circuit is simply an internal junction diode that tracks the junction temperature near the output transistors. When forward biased it can provide an indication of the temperature change, but not the actual temperature. The forward voltage of the diode changes approximately -2.2 mV/°C. The last paragraph on Pg. 21 of the datasheet provides more information about the function. The TMP411 provides a precise way to determine the actual junction temperature when used in conjunction with the TSENSE diode. We don't have any additional information regarding application of the diode as a stand alone element.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Genius 11135 points
    BGX51

    We haven't heard back from you so we assume this answered your questions. If you need additional help just post another reply below.

    Thanks
    Dennis