[SI-LIST] Re: Regarding Output Voltage Rise time of linear Regulators.

Dear Vivek,

You say you are interested in regulation time; I assume you may be 
interested in both small signal
and large signal transient response times.  Start-up and large-signal 
transients, as Orin pointed out,
may be primarily current limited, and you can also expect significant 
nonlinearities in the response.

For small-signal transients, you have a control feedback loop and the 
response time will be
determined by the closed-loop bandwidth.  The closed-loop bandwidth has 
a few contributors,
such as the poles and zeros of the error amplifier plus your capacitors 
on the output.

In either case, unfortunately the formula you are suggesting may give 
you a correct answer only
by pure coincidence.  If you use a linear regulator from a vendor, they 
should have information
available on the response time.  If you build your own, you need to 
calculate the response of the
feedback loop based on the components you use.  If you are faced with an 
unknown black box,
another option is to put it on a bench and do some quick tests.

Regards,

Istvan Novak
SUN Microsystems


Vivekkumar M-TLS,Chennai wrote:
> Dear All,
>  
> We need to find the output Voltage regulation time of linear regulators.
> Generaly when using LDO's(Linear Dropout Regulators) the Output Voltage
> regulation time is given by the manufacturer himself. But in the
> scenario when data is not avaliable in the spec, please can any one
> confim if the following method is acceptable:
>  
> (Input Voltage - Output Voltage)/Load Current =  Series pass resistance
> Value.
>  
> Let this resistance value be Rs.
>  
> We will have adjustable resistors which provides a feedback of the
> output voltage. Let them be Ra,Rb.
>  
> Hence using Thevenin's theorem,
>  
> The effective resistance would be Rs + (Ra II Rb) = Reff.
>  
> The Effective output capacitance will be the total capacitance added at
> the LDO output. = Cout.
>  
> Hence the Regulation time ( Load changing from 10% to 90%) = t 5*Reff*Cout.
>  
>  
> Requesting everyone to give their comments on this.Your immediate
> response will be sincerely appreciated.
>  
> Regards
> Vivek
>  
>  
>
>
>   

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