This is a battery charging circuit. The part I don't understand is the block on the lower right. What does that dashed rectangle mean, the ellipse around the resistor? and the encircled dots?

The datasheet is here.

enter image description here


3 Answers 3


The dashed rectangle typically means a remote part, off-board, or removable. In context this is a battery charger for a removable battery pack, as you see in the description right above that typical application you screenshotted.

The resistor isn't a plain resistor. It's a NTC temperature sensor. Its resistance changes as the temperature does. Typically used as feedback of battery status. If it's too hot, it signals the charger to stop. See page 16 for how the NTC functions here.

And the encircled dots are jacks. Like RCA jacks. Just a simple connector. Typically that symbol is used for 2 conductors (center dot and the outer circle) but here it's been made a bit abstract.

  • \$\begingroup\$ Specifically any coaxial jack or plug, not necessarily a jack but necessarily coaxial--other types of connectors will use other symbols. \$\endgroup\$
    – Hearth
    Commented Feb 9, 2022 at 3:50
  • 4
    \$\begingroup\$ I think the dashed rectangle indicates the parts are located together, not that they're external \$\endgroup\$ Commented Feb 9, 2022 at 12:11
  • 1
    \$\begingroup\$ @user253751 I've seen it used in multiple ways. But here specifically the app note for this one does explicitly call it removable battery pack, while other applications in the same datasheet lack it. \$\endgroup\$
    – Passerby
    Commented Feb 9, 2022 at 16:31

The resistor with the ellipse is a thermistor with a beta value (B) of 3380. The beta value describes the resistance versus temperature curve. The dashed box indicates that the thermistor is thermally coupled to the battery so the device can measure the battery temperature. Should the battery temperature increase to an unsafe level, the charger will so something to prevent over temperature. See data sheet page 7, NTC (Pin 8); and page 16.


What does that dashed rectangle mean

indicates that the parts shown inside are a single module

the ellipse around the resistor?

It means it's a thermister, a circle would indicate a photo-conductor

Being inside the box with the battery it's probably meant to be thermally connected, eg with aluminium tape.

and the encircled dots?

I'm guessing it indicates some sort of connector.

Oddly they don't show a connector for the ground end of the battery or thermister

It is an accepted symbol for a coaxial connector, but here they are surely using it to mean single-wire a join. Odd.


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