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TLE2426: Decoupling advice using a TLE2426

David Tickner
Prodigy 50 points
Part Number: TLE2426
Other Parts Discussed in Thread: LM324,

I am trying to create a small twin stereo audio pre-amplifier to correct a small level correction problem between two audio units which looks to need a gain factor of 3 to 5. I have 10v to work with and will see if a LM324 (for that high frequency limitation) or TL074-84 (for that higher frequency lift) approach would suit these units, to make this work I will need to generate a split rail and think of using a TLE2426LP to do this.

My query is about capacitor decoupling of this split rail in both directions, what values to use if any for best working?

There is of course negative generators using various methods for low level working currents but I find that its about stopping the audio circuits picking up its switching noise, or for that matter any digital chips or radio (FM as well) getting upset, my favorite method is a 4049 which I used to make an ESR tester with at 100KHz, this gives a good output voltage when used as a voltage doubler or splitter with low battery consumption (until loaded) but also great  for knocking out FM radio (I know should be in a metal/screened box).

Think this might be a bit over the top though for just a small gain so return to the TLE2426LP, I am aware of its other version with a decouple pin, just wondered about its rail decoupling?

Thanks for any guidance

David

  • 0
    TI__Mastermind 23050 points
    Hi David,

    The decoupling is similar to what you would use on the supply pins of an amplifier, but since it is buffered you don't really need a bulk capacitance to source the charge for the rail (at least not on the input side). The capacitor is going to see an equivalent resistance of 110kOhms, so this will impact the charging and response to anything happening on the input rail. You should scale your capacitance based on the noise you want to filter out and how quickly you want the splitter to track changes on the input supply.
  • 0
    TI__Guru* 93105 points

    Hi David,

    I used to cover the TLE2426 and have experience with applying the device. The noise reduction pin is a high impedance input. The datasheet lists an equivalent noise impedance of 110 kilohms. Therefore, the decoupling capacitor doesn't need to be very high in value to be effective at audio frequencies. A capacitor value of 100 nF is adequate for many applications, but can be made 1 uF or larger if filtering needs to extend to real low frequencies.

    One thing we did learn is that rather than using a single capacitor to ground, using one capacitor to each supply results in a much faster output voltage rise time for the TLE2426. You can see this in the simulation results shown below.

    Regards, Thomas

    Precision Amplifiers Applications Engineering