Single-cell Li-Ion charger with USB input
The Texas Instruments LM3658SD-B/NOPB is a single-cell lithium-ion/polymer battery charger IC designed for USB-powered applications. It charges one cell to the standard 4.2V termination voltage with a programmable constant-current charge rate up to 1A. The USB interface means the part integrates the logic and power path for a USB VBUS input, handling enumeration or current-limit negotiation without an external controller. The 6V maximum supply voltage covers USB 2.0 (5V nominal) with margin for cable drop.
Thermal and layout: 10-WSON exposed pad
The 10-WSON package (3x3 mm, supplier device package 10-WSON) with an exposed pad requires a thermal land on the PCB to dissipate heat from the pass element during constant-current charging. Surface-mount assembly with the exposed pad means the reflow profile must wet the centre pad — a voided solder joint under the pad raises junction temperature and triggers the over-temperature protection earlier than expected.
Protection set and charge termination
Built-in fault protection covers over-current and over-temperature conditions. The over-current limit is tied to the programmed charge current; the thermal regulation loop reduces charge current if the die temperature exceeds the threshold, preventing thermal runaway without a hard shutdown. Charge termination is based on the constant-current / constant-voltage (CC/CV) profile typical of Li-ion chargers. The 4.2V regulation voltage is fixed; the charge current drops as the cell approaches full charge, and the IC terminates when the current falls below the end-of-charge threshold.
The moisture sensitivity level (MSL) for the 10-WSON package is typically MSL-1 or MSL-3 — store the reels in a dry cabinet or bake before reflow if the moisture barrier bag is punctured.