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LM4040: Settling time

Leo Mirkin65
Prodigy 150 points
Part Number: LM4040

Hello,

Figure 6 on page 32 of the LM4040-N datasheet shows input voltage step response for the LM4040-N-2.5: approximately 40 µs after input voltage is applied the voltage reference reaches its nominal voltage of 2.5 V. Does this imply that it has also settled within that time and performs to specifications?

If not, what is the setting time?

Thank you,

Leo

  • 0
    TI__Mastermind 19580 points
    Hi Leo,

    We do not specify a start up time with this device but the start up depends on the voltage option selected. As you commented, that graph should be a typical graph without a CLoad and it should be around 40-50 us. Because this is not a EC specification, I do not have a maximum worst case start up time so I would design around this with a buffer for temperature deviation. With a CLoad the settling time will be larger depending on the size of the capacitor.

    -Marcoo Z
  • 0 in reply to Marcoo Z
    Prodigy 150 points

    Hi Marcoo,

    I understand the graph shows typical performance without a capacitive load, and depends on the voltage option.

    What I'm asking is whether the graph represents settling time; it is titled "step response," which is related, but not the same.

    Given the same test conditions as above, is additional time required for the reference to perform to the specified tolerance, noise level?

    Thank you,
    Leo

  • 0 in reply to Leo Mirkin65
    TI__Mastermind 19580 points
    Hi Leo,

    You can treat the graphs labeled as "step response" as start up in this situation because the step response is from 0V. I would add some additional time for device to device variation and temperature variation because this is just one device at 25C.

    -Marcoo Z
  • 0 in reply to Marcoo Z
    Guru 140200 points
    Hi Leo,

    you should also read the datasheet of LM4040 (not LM4040-N). See section 8.2 and especially section 8.2.2.5. But, as Marcoo already mentioned, allow the decoupling cap in parallel to the LM4040 to fully charge, too.

    Kai
  • 0 in reply to kai klaas69
    Prodigy 150 points
    Hi Kai,

    That (i.e. section 8.2.2.5 in the LM4040 datasheet) is exactly what I was looking for. Thank you!

    What is your take on the output capacitor value? (If charge time is not a concern. )

    Best Regards,
    Leo
  • 0 in reply to Leo Mirkin65
    Guru 140200 points
    Hi Leo,

    the output capacitor value depends on application. This can be no cap, 100n/X7R or a tantal from 1µ to 10µ.

    Kai