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My schema works as long as the Battery is attached to it.

In fact, it even works if I disconnect the Battery - EXCEPT that the LED1 toggles in that case.

My intention is to use the circuit either

  • 5V and Battery connected (to make the battery charge)
  • Battery-only (normal usage)
  • 5V only connected (for programming and quick tests)

The LED1 toggles wildly in mode 3 (5V without battery-connection). Why ??

enter image description here

The left hand side shows the 5V-to-3.3V conversion (including U1 so that 3.3V is still produced when 5V USB is disconnected)

The right hand side shows the battery-charging circuit (with its main component MCP73832T).

I already added R4=100k between VDD and STAT - but it did not bring anything - the LED1 is still toggling when 5V is disconnected. Shall I connect R4 between VBAT and STAT instead ??

Any idea what to change to stop the LED1 from toggling for 5V supply without Battery-connected ?

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1 Answer 1

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Most likely C2 is the problem. When the battery is not connected, the MCP wrongly thinking there's a battery due to C2, so it drives Stat low (turning the LED on) then it very quickly charges the capacitor (Stat goes high, the LED turns off), then the capacitor discharges - and repeat.
Try using a smaller value for C2. The data sheet recommends 4.7 uF. You can also just leave this be, if you're only using it for quick tests it's unlikely to be a problem.

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  • \$\begingroup\$ Thank you very much, @LordTeddy, it makes total sense now! I definitively will change C2 to a lower value on my next design. \$\endgroup\$
    – iKK
    Nov 10, 2023 at 12:35

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