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LM4990 Voltage Out

Simon Peacock30
Prodigy 70 points
Other Parts Discussed in Thread: LM4990

Hi There

We are considering using a LM4990 as a driver.  The signal it is driving is 1 kHz sine wave with stepped amplitudes (IRIG) which is generated by a DAC.

From my reading of the data sheet, the AMP can drive about 4Vpp which is OK.

Unloaded, we would prefer slightly more (4.5V unloaded) and a minimum of 3V @ 50 ohm.

The load is isolated by a 100mH 1:1 transformer.

Does this sound feasible?  Am I reading the datasheet correctly??

  • 0
    TI__Mastermind 20085 points

    Hi Simon

    The device must be handled with an input amplitude lower than supply rail and you should take into account the selected input gain to avoid clipping on the output signal, I don't think that this device can work with 4.5 Vpp you probably obtain clipping. Regarding the load you'll get an output power very small because this device is designed to work with 8 ohms.

    Best regards
    José Luis Figueroa
    Audio Applications Engineer | A-Team

  • 0 in reply to José Luis
    Prodigy 70 points
    I understand the power out is small, I am thinking that with 50 ohm, power is only 0.3W. This use is outside the usual but the amplifier may be driving multiple loads so lower impedance (or even higher).
    More important is how close to rail to rail will the output be? The data sheet only considers the power out so makes this a bit hard to estimate.
    My estimate from the distortion graphs is 1/2V from each rail (4Vp) with a differential output of 8Vpp.

    Regards
    Simon
  • 0 in reply to Simon Peacock30
    TI__Mastermind 20085 points
    Hi Simon

    The output maximum amplitude depends of the circuit internal losses. Unfortunately, I don't have a LM4990's board to check output maximum amplitude. I think that the device could be able to deliver a maximum amplitude of 4Vp.

    Best regards
    José Luis Figueroa
    Audio Applications Engineer | A-Team