Microchip MCP73831T-2ACI/OT: PCB footprint and gate checks

The Microchip MCP73831T-2ACI/OT is a single-cell Li-ion/Li-poly linear charger from Microchip Technology. Its package or board interface is 5-pin SOT-23, and its relevant electrical envelope is 3.75–6.0 V input, programmable up to 500 mA class, 4.2 V regulation for -2 code. It communicates or connects through linear CC/CV charger with STAT output. Those fields belong together: substituting a familiar family name while changing package, voltage, sensing port, mount style, current class, or interface behavior can leave a PCB that passes ordinary net checks and still cannot be assembled or function safely.

MCP73831 provides a compact, controlled single-cell charger with charge current set by one PROG resistor and open-drain/tristate STAT behavior.

Common uses include small LiPo USB charging and wearable and sensor batteries. Start with the manufacturer drawing and recommended application, then record the exact ordering suffix alongside the KiCad symbol and footprint. This makes the library evidence reviewable when the part is re-sourced months later.

• Place input/output capacitors, programming resistor, thermal pad, and battery connector close to the charger with short power and ground paths. Give thermally limited linear chargers enough copper to shed heat.
• Separate connector ESD and hot-plug current from the battery-sense/reference ground. Mark cell polarity unambiguously on copper and silkscreen.

Select current from cell specification and SOT-23 heat, place capacitors close, protect USB input, and ensure system load does not prevent charge termination.

• Set charge current from cell capacity, connector rating, USB source, and thermal limit. Check termination, precharge, recharge threshold, battery chemistry, maximum voltage, power-path behavior, and temperature sensing.
• A charger is not automatically a load-sharing power path or cell-protection circuit. Add protection, fuel gauging, source isolation, and system-load management when the product requires them.

Put the support components where their current, thermal, optical, RF, or measurement loops are actually short—not merely where ratsnest lines look tidy. Confirm pin one from the package view used in the datasheet, distinguish top view from mating face or bottom view, and check mask, paste, drill, courtyard, enclosure, and rework access independently. A correct copper pad pattern can still be a bad production footprint when the sensing opening, connector latch, exposed pad, thermal path, or cable volume is wrong.

MakeIRL’s release gate should not stop at “the symbol has the right number of pins.” For this part, a useful gate review combines ERC/DRC with the following package- and function-specific evidence:

1. Check battery chemistry and voltage suffix, input range, charge-current resistor, thermal copper, capacitors, status pins, enable, cell polarity, connector, and temperature input.
2. Check whether system load corrupts termination, whether USB and battery can backfeed, and whether separate overcharge/overdischarge/short protection is present.
3. Check exact manufacturer/package and cell specification; generic charger markings and marketplace batteries are not adequate controlled parts.
4. For Microchip MCP73831T-2ACI/OT, check -2 4.2 V code, AC temperature grade, OT pinout, PROG resistor/current, 6 V max, battery polarity, STAT LED current, heat, and separate protection.

Then run ERC and DRC, refill zones, and inspect the fabrication and assembly outputs. Cross-probe the exact pads named by any finding, compare the BOM MPN with the footprint and electrical limits above, and verify that a real cable, enclosure, antenna, sensor stimulus, load, or thermal path can be tested on the assembled unit. An exclusion is evidence that someone dismissed a marker; it is not evidence that the underlying condition was resolved.

The most expensive errors are usually plausible: a footprint from a sibling package, a breakout-board voltage copied to the bare IC, a headline current used without thermal analysis, or a connector family selected by pitch alone. For Microchip MCP73831T-2ACI/OT, review these failure modes explicitly:

• Using a 2 kΩ PROG resistor for roughly 500 mA without thermal analysis can overheat the tiny package or exceed a small cell's allowed rate.
• Setting 1 A charge current in a small linear package from 5 V without checking dissipation at a deeply discharged cell.
• Calling a charger battery protection and omitting the cell's overcurrent and undervoltage protection path.

Sourcing note. Use MCP73831T-2ACI/OT exactly; other regulation-voltage and temperature/package codes are not battery-chemistry substitutes. The approved vendor list should preserve manufacturer, full suffix, package, voltage/range/accuracy grade, lifecycle, and mating or external components. An alternate is real only after its datasheet, land pattern, electrical behavior, firmware assumptions, and assembly process have all been compared—not because a distributor search places it in the same parametric row.