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LDO 2989 Turn on time is not matching

Deepak Chikane
Prodigy 200 points
Other Parts Discussed in Thread: LP2989

Dear Sir,

I have used the LDO2989 Regulator in one of my project.

Part no is:

Problem is that,

I have used the Cbypass=10nF,Error resistor=330K as per Datasheet for the minimum 50uS time.

but at actual my output is rising after 2.5mS.

Here i have attached the schematics and the Turn on time Images

  • 0
    Prodigy 200 points
    in my schematics:C10=10nF/50V is there shutdown signal is 2V From linear supply.
  • 0
    TI__Mastermind 22610 points

    Hello Deepak,

    The LM2989 Start-up time is affected predominantly by the value the Cbypass capacitor, and to a lesser extent by the device temperature.

    Unless the output capacitance value is huge it will not have very little affect on output voltage start-up time.

    The /ERROR pin pull-up resistor value has no direct effect on output voltage start-up time.

    Attached below is Typical Characteristics plot with Cbypass = 10nF

  • 0 in reply to Donald Jones
    Prodigy 200 points

    Hi Donald,

    Thanks for your help.

    i removed the 10nF Capacitor and kept it open now the Rise time is 100uS.

    But i am facing another problem for Turn off time.

    It takes almost 10ms to go low when shutdown pin pulled to low.

    My output load is 330 ohm at output of +5V with capacitor 4.7uF/25V

    Shall decresing capacitor will give the better results.

    Recommended capacitor is min 3.3uF

    Look forward to hearing you soon.

  • 0 in reply to Deepak Chikane
    TI__Mastermind 22610 points

    Deepak

    Turn-off time is just Cout discharging through the load, basically a RC time constant.

    A smaller Cout value, or larger load current will cause faster discharge time.

    There are some LDOs available that have a Special Feature called 'Output Discharge', to speed up the discharge of the output capacitor when the LDO is disabled.

  • 0 in reply to Donald Jones
    Prodigy 200 points

    let me know the Fast output discharge LDO..??

  • 0 in reply to Deepak Chikane
    TI__Mastermind 22610 points

    Here is the link to the Regulator Parametric search page, with the 'Special Features' flag set for 'Output Discharge'. You will need to set additional parameters, and perhaps set additional flags, to narrow down the choices ... Here

    http://www.ti.com/lsds/ti/power-management/single-channel-ldo-products.page?#~p2192=Enable;Output Discharge