3.3 Curiosity Nano Base for Click boards™ Battery Charger

The board has an MCP73871-2CC battery charger for 4.20V Li-Ion/LiPo batteries with 2-pin JST B2B-PH connectors.

When connecting a battery with an external power source, the MCP73871 will charge the battery at a maximum current of 500 mA. When removing external power, the MCP73871 will source power from the battery to power the board. Customize the battery charge current by replacing resistor R7. The charge current follows the formula I = 1000V/R7. The default charge current is 500 mA.

Warning: Only use Li-Ion/LiPo batteries with a nominal voltage of 4.20V and batteries that can handle a charge current of 500 mA or more.

Info: The battery can be connected/disconnected with the slider switch at the upper right corner of the board.

The default input current is limited to 1.8A. If a battery is connected, the board’s current is prioritized, and any available current not required by the board will be used to charge the battery.

The input current limit can be changed by adjusting the configuration of J9, J10, J12, and J13, as shown in the table below.

Table 3-2. MCP73871 Input Current Limit Settings
J9	J10	J12	J13	MCP73871 Current Limit [mA]
Open	Closed	Closed	Open	80 to 100
Open	Closed	Open	Closed	80 to 100
Closed	Open	Closed	Open	1500 to 1800
Closed	Open	Open	Closed	400 to 500 (default)

Warning: All combinations not listed in the table above are invalid and will cause a short circuit between the input voltage and ground.

When the board is supplied by a battery, the only limitation regarding current is caused by the voltage regulators. The maximum output current from the two regulators, MCP16417 and MIC33050, is listed in the table below.

Table 3-3. MCP16417 and MIC33050 Output Current Limit
Regulator	Input Voltage [V]	Output Current Limit [mA]
MCP16417	4.4	1000
MCP16417	4.2	850
MCP16417	3.6	600
MCP16417	3.2	480
MIC33050	5.0	600

Info: The maximum output current for the regulators can be higher if a lower output voltage is tolerated by the regulators.

If the Curiosity Nano Base for Click boards™ is powered by a Curiosity Nano microcontroller board using USB, the current limit is 500 mA.

If the battery is attached to the back of the board in the designated area, a thermistor can be mounted in footprint TH1 to enable the thermal protection feature in the MCP73871. Remove R21 when mounting the thermistor. As an example, using a 10-kΩ NTC with a β parameter of 3590 allows charging between approximately 4°C and 43°C.

Three status signals from the MCP73871 are connected to LEDs located at the upper edge of the board. The table below shows the different LED combinations.

Table 3-4. MCP73871 Status LEDs
S1	S2	PS	Status
Off	Off	Off	Shutdown/no power
Off	Off	On	Shutdown/no battery connected
On	Off	On	Battery charging
Off	On	On	Battery charge complete
On	Off	Off	Low battery output
On	On	On	Temperature/timer fault

Table 3-5. Default Component Values
Designator	Default	Comment
J9	Closed	MCP73871 current limit setting
J10	Open
J12	Closed
J13	Open
R20	Not Mounted	Battery switch bypass, solder 0 Ohm to permanently connect the battery to the MCP73871
R7	Mounted, 2 kΩ	Sets the battery charge current
R21	Mounted, 10 kΩ	Battery thermal protection feature of the MCP73871
TH1	Not Mounted	Battery thermal protection feature of the MCP73871