pole zero tracking frequency compensation LDO

[davyzhu]

ldo questions

Hello all,

I have used Micrel's LDO mic2950*, but how about the parameter IGND
(Typ) and VDropout (Typ), what does they mean, thanks.

My workmates told me LDO is much easy to use than switch, is that true?

BTW, I found the Vout relied only on R1 and R2 (they are adjust resisters), and have no relationship with Vin, why?

Regards!

Davy Zhu

 

[mami_hacky]

ldo power loss calculation

LDO is beeter than switcing Reg. if your current need is low!

 

[Hughes]

ldo loss

IGND may be the current flows into ground. This current is consumed by the LDO and have no contribution to the load circuit. Sometimes it is called excess current.

VDropout is the minimum voltage difference between Vin and Vout with Vout in the specified range.

Vout is determined by the internal voltage reference and the feedback resistors (R1 and R2). It is not dependent on the input voltage provided the input voltage is high enough. This is the essential function for a voltage REGULATOR.


Another way, the switch may bring you more noisy. So if you want to supply the analog circuit, please careful. But the switch fits for the large current, which can supply 10A current. The the efficency of the switch is also high, above 80%, so you do not have the temperature problem.

 

[minaflying]

sample ldo questions

in fact,the switch's noise is a fatal problem in some systerms.many engineers want to find their solution about the noise.

 

[frankon_o2]

questions to ask ldo

may be IGND is the current limit value when output of LDO is short to ground? the droped voltage is consumed by LDO it self, so for a LDO
(Vin-Vout)/Vin of power is wasted, that's why we try to make VDropout as small as possible.

 

[nicleo]

ldo noise site:edaboard.com

LDO voltage regulator is useful for portable application. Let's say you need regulated 5Vdc supply for your circuit. This can be achieved by conventional linear voltage regulator. However, conventional voltage regulator, e.g. 7805, needs higher I/O voltage different (Vin-Vout, e.g. > 2V) to work properly. FOUR 1.5V AA batteries are not enough to provide the required voltage difference (6V - 5V = 1V). Therefore, we see some portable devices use SIX 1.5V batteries or a 9V battery. If we replace the conventional voltage regulator with LDO type voltage regulator (with VDropout < 1V), then it's possible to use just FOUR 1.5V batteries, which will result in smaller/lighter design compared to that equipped with SIX 1.5V batteries.

9V ---(7805)---> 5V
is not efficient. For example, if your circuit draws 100mA, the power loss (at 7805) is about 0.4W.

6V ---(LDO)---> 5V
is MORE efficient. For example if your circuit draws 100mA, the power loss (at LDO) is ONLY 0.1W.

Switching regulator provides higher efficiency. To use switching regulator in sensitive analog circuit, noise filtering [which might increase cost, take up extra space due to bulky inductor/capacitor, etc] will be a challenging design issue. As a result, LDO is still a preferred choice in sensitive analog circuit, e.g. high resolution ADC conversion circuilt modules.


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Added on 26 Sept 2004
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May be the following articles may help:

Linear and Switching Voltage Regulator Fundamentals, Part I and Part II
**broken link removed**, **broken link removed**

Choosing the Right Power-Supply IC for your Application
**broken link removed**

Selecting power management components for portable appliances: LDOs vs switching regulator
[url]http://dataweek.co.za/news.asp?pklNewsID=11440&pklIssueID=343&pklCategoryID=46[/url]

Linear vs Switching Supplies: Weighing All the Options
**broken link removed**

Charge Pump-LDO Chip Offers Option for Generating Low-Noise Supplies
**broken link removed**

Multiple linear regulators power handheld devices
[url]http://www.commsdesign.com/design_corner/showArticle.jhtml?articleID=16505371[/url]

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[layes]

limited duty officer questions

use big transistor

 

[fashion]

ldo quesstions

LDO is good to use but the effincent is worse than switching DC-DC converter.

 

[shanjoyce2004]

ldo versus switching

Vdrop means how high the possible Vout

 

[cathyyang]

questions to ask an ldo applicant

Vdrop is the minimum difference voltage between Vin and Vout when Vout drop to 98%*Vout(typical stable output voltage).
Vdrop=Vin1-Vout1, Vin1 is the input voltage when Vout=Vout1, Vout1=Vout(tpy)*98%