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I want to make a circuit that will provide 2.05V regulated DC from the li-ion battery voltage range of inputs (3.3V - 4.1V).

The load is almost nothing, approximately 0.1mA. However, this regulator must be extremely low-power-draw, ideally not drawing more than 1mW.

Any suggestions for the simplest possible circuit that can accomplish this?

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  • \$\begingroup\$ Can you describe where the 2.05V spec comes from? That seems really precise. I ask because the super-low-current LDOs have trade off performance for their low ground pin current. Dynamic line/load response will suffer for sure, but check DC specs carefully too. \$\endgroup\$ – markrages Aug 2 '13 at 7:34
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There are several low quiescent current adjustable output low drop-out linear regulators that meet the criteria given in the question. The parametric search on the web sites of several of the usual LDO manufacturers would yield some options.

For instance, Texas Instruments TPS76201-Q1:

  • Adjustable Output Voltage: 0.7 V to 5.5 V
  • 27 uA Quiescent Current at 100 mA load
  • 1 uA Quiescent Current if the enable pin is driven high

The typical application circuit is simple as well:

Schematic

At the stated operating conditions, power dissipation in such linear regulators is:

P = (4.1V - 2.05V) * 0.127 mA = 0.26035 mW in a worst-case calculation.

P = (4.1V - 2.05V) * 0.1 mA + (4.1V * 0.027 mA) = 0.3157 mW in a worst-case calculation. (Thanks, markrages, for the correction)

Still well under the 1 mW power budget specified in the question.

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    \$\begingroup\$ Your calculation is wrong because the 27 uA current is dissipated over Vin, not just the Vin-Vout drop. Add an extra 2.05V * 27uA = 55 uw and get 315 uw. And watch those sig figs! \$\endgroup\$ – markrages Aug 2 '13 at 7:43
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    \$\begingroup\$ Also from the datasheet: "Resistors R1 and R2 should be chosen for approximately 10-uA divider current.". So that's an extra Vin*10uA, say 40 uW, for a total of 355 uW. Still meets spec. \$\endgroup\$ – markrages Aug 2 '13 at 7:48
  • \$\begingroup\$ @markrages The R1 and R2 values sit on Vout not on Vin, In any case, like you said, hardly any impact on the final power budget. \$\endgroup\$ – Anindo Ghosh Aug 2 '13 at 8:00
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    \$\begingroup\$ @AnindoGhosh: The resistor divider is on Vout, but since it is a linear regulator, any additional current taken from the output just adds to the current draw at the Vin terminal. Therefore, the 10 uA would be dissipated at Vin. \$\endgroup\$ – Jason R Aug 2 '13 at 11:24
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There are lot of Low Quiscent Current regulators available on market. CHeck the specifications of GND current, Quiscent Current. One of them are 1. ADP160/162/161 - 560nA 2.TPS780xx series - 500nA

there are other regulators with 1uA Quiscent Current like NCP551/NCV551, some from microchip also.

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Another LDO for consideration is STLQ50.

The STLQ50xx is a BiCMOS linear regulator specifically designed for operating in environments where very low power consumption is required.
Its very low quiescent current (3 µA) results in extended battery life, making the device suitable for applications which have very long standby time.

Key Features

  • 2.3 V to 12 V input voltage range
  • 50 mA maximum output current
  • 3 μA quiescent current
  • Available in 1.8 V, 2.5 V, 3.3 V, 5.0 V and adjustable voltage
  • 200 mV dropout voltage at 25 mA output current
  • Internal thermal protection
  • Available in SOT323-5L package, and SOT23-5L package (upon request)

enter image description here

The very small SOT323-5L package option is nice, we use it in one of our battery powered products.

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  • \$\begingroup\$ The first thing you mention is 50 mV dropout, when the original spec indicates any dropout under 1V is fine. I noticed this when searching LDOs: the marketers see the name and think dropout voltage is the most important spec. In reality there are lots of things more important: quiescent current, dropout behavior, noise, etc. (Sorry for the rant -- I spent a full day comparing LDOs recently and was annoyed at the poor selector tools.) \$\endgroup\$ – markrages Aug 2 '13 at 7:40
  • \$\begingroup\$ @markrages: I agree, highlighting the LDO was unnecessary regarding the question, i removed it. I hope its still a potential candidate for your application. \$\endgroup\$ – Rev1.0 Aug 2 '13 at 8:09
  • \$\begingroup\$ @markrages It just so happens that the really low quiescent current devices are also incidentally LDOs / ULDOs. I suspect this is because much research effort goes into reducing quiescent current, throwing in an LDO architecture is a given in such cases. \$\endgroup\$ – Anindo Ghosh Aug 2 '13 at 8:24

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