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OPA454

Johan Kruger
Prodigy 190 points

Other Parts Discussed in Thread: OPA454

I am using the OPA454 in a inverting amplifier design, powered by +24V and -24V. I have the E/D Com pin connected to GND and have the E/D pin connected to +24V. Exactly according to the schematic in Figure 68 on your datasheet.

  1. Is this configuration fine, if so why do I feel some heat genrated by the devices.
  2. If this configuration is wrong, why is it proposed as a Thermal Protection circuit test.
  3. What is the right configuration as I do not monitor the Status FLAG and thus have left it OPEN / NC
  • 0
    TI__Guru 68776 points

    Hi Johan,

    Thanks for your question.

    The OPA454 will dissipate approximately 154mW with no load and ±24V supplies (48V x Iq=3.2mA). This is probably enough to feel some slight warming without a heat sink. Load current will add to the power dissipation and make the device feel warmer. It’s not clear whether you have a load.

    In order to understand your problem more fully, would you please provide a full schematic of your system? I see that you are referencing Figure 68 above, but I need to know more details about the load that the op amp is driving and how much current it may be drawing.

    You mentioned that you have left the Status FLAG pin OPEN, but Figure 68 shows that it should be pulled up to V+ with a 1M resistor.

    Also, how is the E/D pin connected? For output enabled, you may leave it OPEN, or forced HIGH, but it must not exceed 5V above E/D Com (in this case, E/D Com is tied to GND, so E/D must be less than 5V).

    Along with the schematic, please provide a scope capture of Vin, Vout, and FLAG.

     

    Thanks and regards,

  • 0 in reply to Ryan Andrews
    Prodigy 190 points

    Hi Ryan,

    Thanks for the prompt response, I did not take congnecance of the Iq = 3.2mA @ Io ~ 0mA... And I have 40 of them in close proximity, I did make provision for a heatsink... I have these on a cPCI - RTM that is used to drive 8 Synchro's = a 10k load @ 400hz.

    As far as E/D goes, it is pulled up to 24V with a 100k resistor. And yes Status FLAG is left open at this stage...

    4645.SyncroDrive - OPA454.pdf

    6114.SyncroDrive - OPA454 - PWR.pdf

    Thanks and Regards,

  • 0 in reply to Johan Kruger
    TI__Guru 68776 points

    Hi Johan,

    Thank you for the schematics. I looked them both over, and the only recommendation that I would make is that E/D (pin 8) cannot be pulled up to VCC_22V with the 100k resistor (R176). Please ensure that the voltage at this pin does not exceed 5V above E/D Com.

    Feel free to let us know if you experience other problems with your circuit.

     

    Best Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 190 points

    Hy Ryan,

    Thanks for the feedback, it is great to have someone to at least have once overs on a problem.

    I am going to change the 100k to a higher value as suggested in the datasheet, to feed 50uA into the E/D pin... Works out to around 440k, will have a look and see what I have in stock.

    Regards,