MCP73831 is a single-cell Lithium-ion, Lithium-Polymer batteries charging controller chip. What do we mean by charging control is that this chip acts a interface between the power input and battery there by performing the below operations:
- Providing constant current to battery for charging
- If the charging input falls below a certain voltage (called under voltage lockout), this chip enters Automatic power-down there by eliminating any power drain from battery
- Reverse charge detection
- Tri-state charging status output from the chip
- Accept input from USB cable
- Employs Constant Current Constant Voltage algorithm for charging battery
- Constant current for charging can be programmed through an external resistor
- Input Voltage: 3.75V to 6V
Constant Current Constant Voltage Algorithm curve:
Source: TDK Lambda
Pin out of MCP73831 is as below:
Circuit Design:
Charging Current:
The constant current for charging the battery can be calculated using,
I = 1000/R => For 10K resistor, I = 1000/10 = 100mA
In the above equation, I is in mA and R is in kohms.
which also is confirmed by the below values from datasheet.
One important point to remember here is that for 250mAh battery, the charging must be 250mA for good battery performance.
Power dissipation:
Power Dissipation = (VDDmax - VPTHmin)* IREGmax
VDDmax = 5V from power source
VPTH / VREG = 66.5% => VPTH = 0.665*VREG => VPTH = 0.665*4.2 => VPTH = 2.793V
Here, VREG is your battery maximum voltage.
Power Dissipation = (5 - 2.793) * 100m => 0.22W
Thermal resistance of SOT-23
So, for 30deg, Temperature Rise is,
=> 30+(230*0.22) => 80.6deg
The above value is below the operating temperature specification of the chip. Snapshot of oeprating temperature below.
External capacitors:
Minimum of 4.7uF capacitor on the VBAT pin.
Schematic Diagram:
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