I have a circuit with a PIC18 whit USB that uses a MCP73831 for battery charging.
The +5V from USB goes in to the MCP73831 with a 4,7uF ceramic capacitor on the input and one
on the output, and then the battery. The PROG resistor is 2k, which would give 500 mA (the
battery is 3000 mAh). After the battery I have a MCP1802 LDO with +3,3V output.
Here is my problem;
If I have no battery connected the PIC18 some of the time will not start up, most of the time it
starts up, but my computer says it can not recognize the device (it should be a simple CDC which
echos back the data sent to it (the examples in the Microchip libraries)).
When the battery attached the computer recognizes the device properly, every time. I have a
100 nF capacitor on the MCLR-pin of the PIC which helps somewhat.
If I bypass the MCP73831 (with no battery attached off course) and the +5V from the USB goes
directly to the LDO the PIC starts up properly and the computer recognizes the device every
time, no exceptions.
So, I guess my question is, how will the MCP73831 work when there is no battery attached?
Or is there something else that is wrong with my connection?
I have made a similar circuitry earlier with the MCP73831 but a different PIC (without USB) and that
PIC did not start either without the battery.
And if you wounder why I do not want to have the battery attached it is because I need the battery
elsewhere at the moment, and, during development it would be nice not to have the battery.
Thanks in advance! If I was unclear about anything please tell me so I can make it clearer :)