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I'm planning to use the MCP1825 LDO regulator to be used with a 3.7V LiPo battery to power up a circuit with 3.3V requirement (microcontroller + ESP8266). However, I'm confused with which package to go with.

MCP1825 comes in a SOT223-3 and SOT223-5. The later offers two extra pins: Shutdown and Powergaurd. I'm not able to comprehend the datasheet as to why these two extra pins are provided.

Does it mean that once my battery voltage is below certain voltage (such as 2.7V), it will shutdown regulation and prevent over discharge? If yes, how do I set that limiting voltage? Should a SOT-233-3 package be sufficient to provide 3.3V regulated output?

Datasheet Link

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    \$\begingroup\$ Power Good not Guard. The first page in the datasheet explains it pretty well. \$\endgroup\$
    – Mike
    Oct 8, 2017 at 18:39
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    \$\begingroup\$ LiPo ranges from \$3.0\:\textrm{V}\$ when fully discharged to \$4.2\:\textrm{V}\$ when fully charged. The worst case dropout voltage of the MCP1825 is \$350\:\textrm{mV}\$. Given your \$3.3\:\textrm{V}\$ output, you will only be able to use your LiPo (with certainty) down to its own voltage of \$3.65\:\textrm{V}\$. Since that is close to the "nominal" voltage, I'm not sure how good your plans are. Also see: electronics.stackexchange.com/questions/38782/… \$\endgroup\$
    – jonk
    Oct 8, 2017 at 18:50
  • \$\begingroup\$ which gives the lowest thermal resistance, e.g. the best removal of heat? \$\endgroup\$ Oct 8, 2017 at 23:16

2 Answers 2

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You need to add your own UVP protection for LiPo to drive enable signal.

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The shutdown pin is for connecting an external voltage detector (such as the Microchip MCP112 or TC54) to shut off the circuit if V_In drops below a certain threshold. This can be done to protect the battery from damage due to deep discharge.

The power good output (PWRGD) pin can be used to detect when the LDO enters the dropout zone. For example, for enabling a low-battery signaling LED or something like that.

If you don't need those features you still have to connect them in a useful way because you can't let them floating. For example, connecting SHDN to V_in should be fine.

Alternatively, you can simply use another LDO that comes without these features, such as the MCP17002E-330. See also my answer to a related question where also another more efficient LDO is discussed.

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