LDO Regulator question

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#1
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If i'm not mistaken my input voltage should by all means larger than my desired fix out put voltage right? But i came across a LDO regulator that can accept a minimum of 2.2V and my fix output is 3.3V. Does it mean that, i still get my 3.3V output even i really do supply my LDO with 2.2V input?

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If it is the case it must be a mislabeled buck-boost converter.

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Which LDO?

Leon

Leon Heller G1HSM

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The LDO i'm referring to is a LP2992 http://de.farnell.com/national-semiconductor/lp2992aild-3-3-nopb/ldo-reg/dp/1685690?_requestid=901902 sorry, it's in german, but it's stated there, minimum supply voltage is 2.2V

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Check the data sheet on p 5 - Note 7!

Leon

Leon Heller G1HSM

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Thanks for the tip, really appreciate it. So i read the Note 7 and i understand from the text that Vin must be greater than 2.2V and Vin must also be greater than Vout(nom) + Vdo and Vdo is Vin-Vout. I hope i got these correct.

But i dont understand this phrase.

Quote:
Dropout voltage is defined as the input to output differential
at which the output voltage drops 2% below the value measured with a 1V differential.

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The differential is Vout-Vin; you just have to ensure that it is larger than the dropout voltage defined above otherwise the regulation won't be very good.

Leon

Leon Heller G1HSM

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what doea it mean with the '1V difference'?

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Vin-Vout = 1V

Leon

Leon Heller G1HSM

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that means that by all means will my Vin at least 1 Volt more than my Vout if i want my regulator to function properly.

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No, the dropout voltage is typically less than 1V for an LVO.

The dropout voltages for the various versions are in the table. You just have to ensure that they are exceeded. You don't have to understand how they are calculated to use them.

Leon

Leon Heller G1HSM

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Quote:
Dropout voltage is defined as the input to output differential
at which the output voltage drops 2% below the value measured with a 1V differential.

I understand this sentence as follows:
It describes, how the dropout is defined. First
you measure the output voltage when the input
is 1 Volt above the output. For a low drop
regulator 1V is large compared with the
low drop, so the regulator operates in a kind of
"safe" area, far away from the critical point
where the output will start to drop. Call This voltage Vnom. Then you decrease the input voltage until
the output voltage drops below 2 percent of Vnom.
Then you measure Vout-Vin and call this Vdrop.
This simply means you carefully approach the point
where the output drops below the nominal voltage.

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oh, thanks for the info. gained a lot. Thanks :D