Load transient calculation

Hi all
the load transient of the linear regulator when Iload varying from 0 to 10m with 1u rise time with an output capacitor of 200p, I want to know that how to calculate undershoot and overshoot voltage change? in my case delta vout = (Iload*risetime)/cout is not working.
it's very helpful if you provide any reference for a better understanding of load transient theoretical analysis like calculation of cout value from transient specification.

best regards

Hi,

it´s a question of the feedbacked regulation loop within the regulator. (which you don´t show nor give any information about it)..
It´s not a simple problem of I_load, risetime, C_out

Klaus

Hi,

Calculate rather with formula in "Transient response" section of below link.
Low-dropout regulator - Wikipedia

At some point, every regulator's HF PSRR becomes a
function of the output filter and not the control loop.
This could be sub-100kHz for an old LM317, or over 1MHz
for some of the newer LDOs which offer improved HF
PSRR as a feature to make them useful as "cleanup"
for higher frequency switching power supplies.

In this case I recommend that first you assign the
risetime an application-realistic worst case; a 1uS
risetime on a large current step is not, usually. That
would prefer to have enough bulk filter to soak up
a lot of the current close-in, and give the control
loop the time it needs to catch up. What does the
load say to expect, or are you just making up test
challenges with characteristics the regulator just
can't be expected to meet?

You also need to consider that at Iload=0, the
control loop might be "wound up" trying to make
zero output current, and respond poorly to the load
step because it's not really closed loop linear. Might
instead do something like 1mA to 20mA, and see if
that behaves better.

1us risetime for a 10mA current step is usual I think, not in final applications maybe, but for testing it isn't surprisingly big. 1A/us slew rate is normal under validation. But I agree anyway.
I think check existing LDO datasheets for parameters and how they are tested, usually manufacturers share these in details.