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LM4755: start up delay for this device

Shawn Workman
Genius 14320 points
Part Number: LM4755
Other Parts Discussed in Thread: LM4911

I have been working with the TINA reference design for this and it seems that the models shows an ~70mS delay for start up or when the devices is muted, then unmuted.

Is this model behavior indicative of the actual part operation?

No delay is mentioned in the datasheet regarding mute or startup.

Shawn

  • 0
    TI__Guru* 84915 points

    Hi, Shawn,

    The TINA reference design has been developed based on linear approximation of charge and discharge times. Ideally, the start up time is around 70ms but in practice this value can be around 0.1 seconds. This TINA model usually shows the actual part operation when the reference circuit and layout guidelines are followed.

    Please let me know if you have additional questions or comments on this.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    TI__Genius 14320 points

    When you say charge and discharge times, are you referring to the bias capacitance or something else?

    If not the bias, what else effects the charge/discharge time?

  • 0 in reply to Shawn Workman
    TI__Guru* 84915 points

    Hi, Shawn,

    The charge and discharge times of the bias pin capacitor and outputs capacitors are important to determine the start up and power down times. You should expect a 0.1 seconds time when the values of the TINA model are used, but the times can be relaxed if these capacitors values are reduced as well.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    TI__Genius 14320 points

    Although, it seems if I set the bias capacitor to 10nF and the coupling capacitor to lower values...still takes ~70mS to start up the output on the simulation.

    Is there an internal charge/discharge inside the device driving this or is the model set to have 70mS no matter what is on bias and the load?

  • 0 in reply to Shawn Workman
    TI__Guru* 84915 points

    Hi, Shawn,

    I have not details on this for this product. But there are some similar devices such the LM4911 that has a minimum wake up time when no outputs capacitors are used and the bias capacitor remains at the recommended value. The min wake up time for this device is 0.5 seconds.

    So, I think that the internal mute circuit is involved in this delay that you are getting.

    Best regards,
    Luis Fernando Rodríguez S.