MCP73831 PCB Design Guide: Footprint, Pinout, and Alternatives
500 mA single-cell Li-ion linear charger with programmable current.
The MCP73831 is the smallest sensible way to put single-cell Li-ion or Li-Po charging on a board: a complete linear charge controller in a SOT-23-5 that needs only two capacitors, one resistor, and optionally an LED. It runs the standard CC/CV profile — preconditioning for deep-discharged cells, constant current set by a single PROG resistor, constant voltage at the ordering-option regulation voltage, then termination at a fraction of the programmed current.
Being linear is both the appeal and the constraint. There is no inductor and no switching noise, but every volt dropped between the 5 V input and the cell is dissipated as heat in a package with limited thermal mass. The chip protects itself by folding charge current back as the die heats, so the current you program is a ceiling, not a promise — at high programmed currents the sustained real-world rate is often lower.
Most MCP73831 problems trace to four things: underestimating dissipation, mis-sizing or floating the PROG resistor, ordering the wrong voltage variant, and running the system load from the battery during charge. Each is covered below.
What breaks boards
It gets hot at 500 mA — thermal fold-back cuts your real charge rate
Charging a low cell (~3.5 V) at 500 mA from a 5 V input dissipates roughly 0.75 W in a SOT-23-5. The die heats until thermal regulation folds the charge current back — the datasheet gives no single regulation setpoint, only the graphical fold-back curve of Figure 4-2 (roll-off from roughly 95–105 °C junction) plus a 150 °C thermal shutdown. In practice a 2 kΩ PROG board often sustains well under 500 mA until the cell voltage rises. Give the part generous copper on the VSS/thermal path, or program a lower current if charge time is not critical.
One resistor sets everything — and a floating PROG means shutdown
Charge current follows IREG (mA) = 1000 V / RPROG (kΩ): 2 kΩ programs 500 mA (505 mA typical per the electrical tables), 10 kΩ programs 100 mA, and 67 kΩ about 14.5 mA, across a usable 15–500 mA range. Leaving PROG open (roughly ≥ 70–200 kΩ) puts the device into shutdown — which you can use deliberately by switching the resistor path with a transistor to gate charging from a microcontroller.
The ordering-code suffix sets the regulation voltage
The MCP73831-2 regulates at 4.20 V — the correct choice for standard Li-ion/Li-Po cells. The -3, -4, and -5 options regulate at 4.35 V, 4.40 V, and 4.50 V for special high-voltage chemistries, and each holds ±0.75%. The suffix is easy to miss on a distributor listing, and a 4.5 V part will overcharge a standard 4.2 V cell. Check the full ordering code, not just 'MCP73831'.
STAT is one tri-state pin, not two status outputs
A single STAT pin encodes charge status by being driven low (charging), driven high (charge complete), or left high-impedance (shutdown/no battery). One LED gives you charging-versus-done. To show two distinct LEDs, use the tri-state trick: two back-to-back LED+resistor legs between VDD and VSS with STAT at the midpoint, so each state lights a different LED and high-Z lights neither.
No power path — do not run the system from VBAT during charge
Like the TP4056, the MCP73831 connects straight to the cell and assumes it is charging a battery, not a battery plus a live load. System current drawn from VBAT during charge distorts the termination measurement — the charger cannot tell load current from charge current, so it may never terminate, or terminate early. For devices that run while charging, add load-sharing (a P-MOSFET/diode circuit) or move up to a charger with an integrated power path such as the MCP73871.
Key specifications
| Parameter | Value | Source |
|---|---|---|
| VDD range | 3.75 V to 6 V (UVLO start 3.45 V typ rising) | DS20001984H, Section 1.0 DC Characteristics, 'Supply Voltage VDD' and UVLO rows |
| Regulation voltage options | 4.20 V (-2), 4.35 V (-3), 4.40 V (-4), 4.50 V (-5), each ±0.75% (e.g. VREG 4.168–4.232 V for MCP7383X-2) | DS20001984H, DC Characteristics 'Regulated Output Voltage VREG' rows |
| PROG resistor → current | IREG (mA) = 1000 V / RPROG (kΩ); tested points: 2 kΩ → 505 mA typ (450–550), 10 kΩ → 100 mA typ (90–110), 67 kΩ → 14.5 mA typ; usable charge range 15–500 mA, PROG impedance range 2–67 kΩ, PROG open (≥ 70–200 kΩ) = shutdown | DS20001984H, Equation 5-1 + DC Characteristics 'Fast Charge Current Regulation' and 'PROG Input' rows |
| Preconditioning threshold | VPTH = 66.5% of VREG typ (64–69%) standard option, i.e. ~2.79 V for 4.20 V parts; 71.5% option also available; precondition current 10%/20%/40% of IREG or disabled | DS20001984H, DC Characteristics 'Precondition Voltage Threshold Ratio' and 'Precondition Current Ratio' rows |
| Termination (% of Iprog) | ITERM/IREG options 5% (3.75–6.25), 7.5% (5.6–9.4), 10% (8.5–11.5), or 20% (15–25), set by ordering option | DS20001984H, DC Characteristics 'Charge Termination Current Ratio' rows |
| Thermal regulation / shutdown | No single setpoint specified: charge current is folded back vs die temperature per Figure 4-2 (roll-off shown from ~95–105 °C junction up to ~150 °C); thermal shutdown TSD = 150 °C typ with 10 °C hysteresis | DS20001984H, Section 4.9 Thermal Regulation + Figure 4-2; DC Characteristics 'Thermal Shutdown' rows |
Verified against the manufacturer datasheet on 2026-07-09. Confirm the current revision before production use.
Alternatives
- TP4056 — 1 A capability with a thermal pad, and the basis of the ubiquitous cheap charger modules; same linear topology and same no-power-path caveat.
- MCP73871 — Microchip's step up when the device must run while charging: adds power-path/load sharing so the system draws from the input, not the cell.
- BQ24074 — 1.5 A with power path and more control pins — more routing work, much better behaved in always-on devices.
Common questions
- What PROG resistor do I use for a given MCP73831 charge current?
- IREG in mA equals 1000 divided by RPROG in kΩ: 2 kΩ gives 500 mA (505 mA typical), 10 kΩ gives 100 mA, 67 kΩ about 14.5 mA. The usable range is 15–500 mA with PROG impedance between 2 and 67 kΩ; a good rule is to program no more than 0.5C for your cell.
- Why does my MCP73831 get hot and charge slower than programmed?
- It is a linear charger: at 500 mA into a low cell from 5 V it dissipates around 0.75 W in a SOT-23-5, and the die folds charge current back as it heats (with hard shutdown at 150 °C). That is by design. Add copper area for heat spreading or program a lower current if the fold-back bothers you.
- How do I wire the MCP73831 STAT pin for charge status LEDs?
- STAT is a single tri-state output: low while charging, high when complete, high-impedance in shutdown. One LED shows charging activity directly; for two LEDs, place two opposing LED+resistor legs between VDD and ground with STAT at the junction so each logic state lights a different LED.
- MCP73831 or TP4056 — which should I use?
- The MCP73831 wins on size and simplicity (SOT-23-5, minimal externals, up to 500 mA); the TP4056 charges at up to 1 A and has a thermal pad to handle the extra dissipation. Both are linear chargers without a power path, so both need load-sharing if the system runs during charge.