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OPA548: Power Amplifier: OPA548 Vs LM675

Marina Iriarte40
Prodigy 170 points
Part Number: OPA548
Other Parts Discussed in Thread: LM675,

Hi,

I need a power operational amplifier with following requiremeents: Vsupply=+/-12V; Ioutmax=0.8A. I found LM675 but in the datasheet it is said that it could have some stability problems with gain under 10. Our application will have a gain of 2. I have also found P/N OPA548, does this part have better stability?

  • 0
    Guru 140200 points
    Hi Marina,

    the LM675 is designed for a gain >10. This does not mean that the chip is bad or less stable than any other OPAmp. No, the LM675 is speeded-up. It's compensated for a gain >10, which makes it faster compared to a chip which is compensated for a lower gain. But at the same time the LM675 cannot be used for a gain <10.

    The OPA548 can be used for a gain of 2. See figure 26 of datasheet. R3 and Rf1 provide a gain of 2. You would only have to omit the voltage divider R1/R2 at the + input of OPA548. Then you will have a total gain of 2.

    Kai
  • 0
    TI__Guru* 93105 points

    Hello Marina,

    Under compensated op amps such as the LM675 often can be externally compensated to assure stability when operated with a gain less than their stated mimimum closed-loop gain (10 V/V) . The LM675 datasheet in Figures 12 and 13 proivde examples of unity-gain amplifiers that are externally compensated. Changing the gain to something higher than unity, but less than 10 V/V, will likely require the compensation to be a little different. In my opinion, unless there is an electrical parametric performance reason for selecting the under compensated op amp, it easier to go with a more conventional unity-gain stable power op amp such as the OPA548.

    The OPA548 shouldn't have any stability issues when operated in a gain of 2V/V, unless the output load is highly capacitive - not a different behavior than that for nearly all op amps. Should that be the case, then it may be necessary to add some compensation to the circuit. The OPA548 simulation model is available and we can use it to help derive proper compensation.

    The OPA548 will easily handle your +/-12 V supply and 0.8 Amp Iout requirements. It would be my choice.

    Regards, Thomas
    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Guru* 93105 points
    Hi Marina,

    Do you need any more assistance with your power op amp application? If you don't need anything more, please click the green "This Resolved My Issue" button so we can close this E2E inquiry.

    Regards, Thomas
    Precision Amplifiers Applications Engineering
  • 0 in reply to Thomas Kuehl
    Prodigy 170 points

    Thank you very much! That was the answer I was looking for :)