I am looking to replace a 1 A switch mode supply with a cheaper (low-drop) linear voltage regulator to power a microcontroller with 3.3 V from 5 V supply (which is stepped-down from 24 V).

According to its datasheet, an LD1086 has 5 mA quiescent current that "flows into the load, increasing efficiency.". What happens if the microcontroller is haltet and only draws microamps?

Also, assuming max. current consumption (70 mA for the CPU without active outputs, plus active outputs) to be 150 mA at 3.3 V, could I use the DFN8 package of this LDO when powering from 5 V?

Approx. 1.7 V drop at 150 mA means 255 mW (1/4 W) loss. DFN8 package has 33 °C/W junction-ambient thermal resistance, so it should be 8.4 K above ambient temp, correct?

Competitor LM1117 in SOT-223 has 61.6 °C/W resulting in theoretical 15.7 K above ambient. The datasheet suggests it needs a tantalum capacitor at the output for stability, which I would like to avoid. What needs to be considered in order to use a ceramic capacitor instead (e.g. murata GRM31CR71C106KA12L)?

  • \$\begingroup\$ Not quite sure why you need low drop capabilities when you have 1.7V of headroom \$\endgroup\$ – PlasmaHH Sep 21 '16 at 10:30
  • \$\begingroup\$ You are right. Do you have a suggestion for a part or could comment on my thoughts? \$\endgroup\$ – handle Sep 21 '16 at 10:38
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    \$\begingroup\$ product recommendations are offtopic here. \$\endgroup\$ – PlasmaHH Sep 21 '16 at 10:41
  • \$\begingroup\$ OK, but it's too bad you're only criticising instead of responding to questions. So I'll just wait for someone else to come along. \$\endgroup\$ – handle Sep 21 '16 at 11:02
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    \$\begingroup\$ I wasn't aware that you are the person entitled for my free time, and I have actually commented on your thoughts about needing an ldo, so what the fluffle do you want? \$\endgroup\$ – PlasmaHH Sep 21 '16 at 11:03

The question about quiescent current looks legit, so I'll answer that. Yes, your circuit should accommodate for quiescent current which can be as high as 10mA in the worst case. If you don't, you can't rely on output voltage anymore.

Clearly LD1086 is not a good choice to power the microcontroller from. It is designed to provide high current (up to 1.5A) which you don't need, and has this minimum current limitation which matters to you. You can probably get away with a much smaller and cheaper regulator, something like a NCV663.

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    \$\begingroup\$ Careful, that almost sounds like a product recommendation, someone may complain that you're going off topic by suggesting a solution to the problem. ;-) \$\endgroup\$ – Andrew Sep 21 '16 at 11:57
  • \$\begingroup\$ @Andrew Frankly, I didn't check the pricing or studied the datasheet in depth, I just wanted to give an example of the kind of devices the OP should be looking for. And I don't think we have a policy against answers which suggest products - only against answers which only suggest a product and nothing more (and incidentally against questions which call for such answers). \$\endgroup\$ – Dmitry Grigoryev Sep 21 '16 at 12:09
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    \$\begingroup\$ I, for one, am glad he recommended it because I didn't know about it and it looks great on paper. \$\endgroup\$ – Edin Fifić Apr 12 '20 at 16:14

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