"Soft-Circuit" for Linear LDO

[Harish Rajula]

Hi
I'm working on design of Linear LDO.I have problem with in-rush current so i need to add a "soft start circuit" wiil give your suggestion on what kind of techniques are there?
and How to overcome that problem.
Thanks.

 

[crutschow]

One solution is to add an NTC current limiter at the input.

 

[D.A.(Tony)Stewart]

Use a Metal oxide Inrush current limiter or ICL. This has a NTC thermal characteristic. Like a Polyfuse but opposite Rtc and comes in many values.

 

[emresel]

Hi;
How about this?
https://www.diy-audio-guide.com/soft-start.html

Hope helps

 

[dick_freebird]

An RC low pass filter on your bandgap core's output, before
the error amp sees it, can be tolerably compact and give you
a reasonable soft-start dV/dt. But what's reasonable, to who,
that wants some digging - opinions surely vary, as they have
to do with input supply capability and all decoupling attached
to the LDO's output. Nobody wants a huge current slug but
a lot of people want no more turnon delay or slowness in
reaching final value, than necessary. But hard to get customers
to give you good quantitative guidance for these "abnormal
operation" type things, unless they've got bite marks to show.

You may want to add some explicit discharge to the vref
delay capacitor, run it off the UVLO function (which needs
a different branch of the vref, without such stuff) for the
case that the upstream supply gets into some sort of
"hiccup" mode from other actors' inrush remands.

 

[D.A.(Tony)Stewart]

Define Input and output voltage, max avg and surge current at present and desired response time and current limit.

Or define the circuit and load which causes the surge.

 

[casemod]

Some LDO's have a shutdown pin. A capacitor on this pin slowly ramps the output as it charges,