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davyzhu
Joined: 23 May 2004
Posts: 521
Helped: 3
Location: oriental
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 24 Sep 2004 10:44 LDO questions |
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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
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mami_hacky
Joined: 28 Mar 2002
Posts: 683
Helped: 4
Location: Some where
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| 24 Sep 2004 12:24 Re: LDO questions |
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| LDO is beeter than switcing Reg. if your current need is low!
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Hughes
Joined: 10 Jun 2003
Posts: 712
Helped: 84
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| 24 Sep 2004 14:07 Re: LDO questions |
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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.
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minaflying
Joined: 24 Sep 2004
Posts: 22
Helped: 2
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| 25 Sep 2004 2:19 LDO questions |
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| in fact,the switch's noise is a fatal problem in some systerms.many engineers want to find their solution about the noise.
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frankon_o2
Joined: 07 Sep 2004
Posts: 8
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| 25 Sep 2004 5:05 LDO questions |
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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.
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nicleo
Joined: 06 Sep 2004
Posts: 717
Helped: 60
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| 25 Sep 2004 17:28 LDO questions |
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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
http://www.national.com/appinfo/power/files/f4.pdf, http://www.national.com/appinfo/power/files/f5.pdf
Choosing the Right Power-Supply IC for your Application
http://pdfserv.maxim-ic.com/en/an/AN737.pdf
Selecting power management components for portable appliances: LDOs vs switching regulator
http://dataweek.co.za/news.asp?pklNewsID=11440&pklIssueID=343&pklCategoryID=46
Linear vs Switching Supplies: Weighing All the Options
http://www.reed-electronics.com/ednmag/archives/1998/010198/01cs.htm
Charge Pump-LDO Chip Offers Option for Generating Low-Noise Supplies
http://powerelectronics.com/mag/power_charge_pumpldo_chip/
Multiple linear regulators power handheld devices
http://www.commsdesign.com/design_corner/showArticle.jhtml?articleID=16505371
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layes
Joined: 27 Sep 2004
Posts: 57
Helped: 2
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| 11 Oct 2004 5:13 Re: LDO questions |
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| use big transistor
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fashion
Joined: 01 Sep 2004
Posts: 27
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| 13 Oct 2004 12:31 LDO questions |
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| LDO is good to use but the effincent is worse than switching DC-DC converter.
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shanjoyce2004
Joined: 11 Nov 2008
Posts: 7
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| 12 Nov 2008 9:34 LDO questions |
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| Vdrop means how high the possible Vout
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