• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 47 subscribers
  • Views 1089 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA548 thermal status signal

Andreas Glatte
Prodigy 70 points
Other Parts Discussed in Thread: OPA548

Hello,

maybe someone can tell me what's the MAXIMUM voltage at E/S pin when there is NO thermal shutdown? In the datasheet (p. 7) there is mentioned only a TYPICAL voltage (of V- + 3.5V).  On p. 17 fig. 29 there is a recommendation for 'reading' that voltage by a FET. All of these FET have a Vgs-Maximum of 20V only. The OPA548 can be supplied  by up to 60V. That's 200% of Vgs_max. There is no detailed circuit in the datasheet where one could see if a limiting circuitry exists.


Regards

Andreas

  • 0
    TI__Guru* 93105 points

    Hi Andreas,

    I had to do some searching to find the answer. The OPA548 maximum E/S pin voltage is equal to whatever the applied V+ level is. I found an older datasheet and it listed it in the Absolute Maximum Ratings table, in the Input Shutdown Voltage line as V+.

    It appears that in a recent revision of the OPA548 datasheet the V+ was accidentally moved from the MAX coulmn, to the UNIT column. You will note that in table 7.1 the UNIT column lists "V+" which wouldn't be the correct unit. It should just be "V."

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 70 points

    Hello Thomas,

    thanks for your answer.

    There are two conclusions. When 'V+' in table 7.1 is really the maximum >output< voltage that can occur, then the FET in figure 28, 29, 39 can die. The other possibility could be that 'V+' in that table is the maximum >input< voltage (a user can apply to the pin without damaging it). In this case the maximum occurrent output voltage is still unclear (the value I expect in the continued table 7.5 on page 7. Hmmm....

    Regards

    Andreas

  • 0 in reply to Andreas Glatte
    TI__Guru* 93105 points

    Hi Andreas,

    The OPA548 E/S pin does not rise up to V+ on its own so the MOSFETs shown in the figures won't be compromised when being used to monitor thermal shutdown. The "V+" maximum applies to the voltage that can be applied to the E/S pin when it is being used for the E/S function. I discussed this with the designer of the OPA548 and he verified that is the intention of the specification. He pulled out the internal schematics and traced out the circuits, and verified they can handle the high voltage.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 70 points

    Hello Thomas,

    thanks for your clarification. So I don't need to insert a protective diode. :-)

    Kind regards

    Andreas

  • 0 in reply to Andreas Glatte
    TI__Guru* 93105 points

    Hello Andreas,

    It should not be necessary to add a protection diode.

    Regards, Thomas

    PA - Linear Applications Engineering