How to determine needed GBW and DC gain of the LDO from spec?

Could anyone explain these to me? Thanks!

Hello, Look at the low Freq in the PSRR, its the same as the DC.
Regards

mosheavi said:

Hello, Look at the low Freq in the PSRR, its the same as the DC.
Regards

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Thanks, anything else except DC PSR to deternmine the DC gain. How about GBW?

qslazio said:

Could anyone explain these to me? Thanks!

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What is the purpose of an LDO? To amplify? I don't think so.
Therefore: What is the meaning of a "Gain-Bandwidth-product" for an LDO ?

LvW said:

What is the purpose of an LDO? To amplify? I don't think so.
Therefore: What is the meaning of a "Gain-Bandwidth-product" for an LDO ?

Click to expand...

I actually mean f0dB of the open loop gain of a LDO. And I borrowed the term GBW from amplifier.
Here is what I think: although LDO is not a amplifier to amplify signal, it does act like a amplifier to reject supply noise or transient load dump. So I guess these performance will be related to the f0dB of a LDO.

OK, QSLASZIO, now I know what you mean.

For this purpose, you have to consider the reference voltage (usually half of the output voltage) as input for a control loop and the varying input voltage as a disturbing parameter.
Then, the control loop has to ensure that the output voltage follows the reference. Therefore the closed loop has a gain of "two". A model of this loop looks as follows:
All parts (opamp, path element) are in the forward path - except the resistive voltage divider (as mentioned: usually 0.5) which is in the feedback path beween Vout and the input unit that subtracts the feedback voltage from the reference.
This is a good starting point to measure/compute/simulate the loop gain and to identify the unity gain frequency.

qslzaio,hello!The closed loop GBW can be caculated from the time you want Vout to settle to a certain value within some settling error,for ex, 1%.Just like the way in which we design the OTA's GBW in ADC design.