Multi-chemistry charger for 2-4 cell packs, 10A ceiling
The Texas Instruments BQ24740RHDR is a multi-chemistry battery charger IC designed for 2 to 4 series-cell Li-ion, Li-polymer, or NiMH packs, with a programmable constant-current charge up to 10 A and a maximum battery pack voltage of 18 V. It integrates over-voltage fault protection and operates from a supply up to 24 V, making it suited for notebook, industrial handheld, and portable instrument charging bays where the battery chemistry varies across production runs.
10 A charge current — sizing the power path
The 10 A maximum charge current is the headline rating for this charger IC. At that level the external MOSFETs, inductor, and sense resistor must be sized for continuous 10 A plus margin; the 28-VFQFN exposed pad needs a solid thermal via array under the paddle to keep the junction below 125°C. The constant-current programming loop accepts a resistor-divider from the ISET pin, so the charge current can be dialled down for smaller packs without changing the board layout.
Obsolete — sourcing and replacement reality
The BQ24740RHDR is officially listed as obsolete by Texas Instruments. No direct pin-compatible replacement is documented in the available records, so new designs should evaluate the current-generation bq247xx family for a functional match.
28-VFQFN package — rework and thermal notes
The 28-VFQFN (5x5 mm) exposed-pad package is surface-mount only. The large centre pad is the primary thermal path and the ground return for the power stage; a poor solder joint under the pad lifts the thermal resistance and can trigger the over-voltage protection during high-current charging. The package outline is symmetric — mark pin 1 orientation on the board silkscreen before the first reflow.