What this charger does and where it fits
The Linear Technology LT3651EUHE-8.4#PBF is a constant-current, programmable Li-Ion/Polymer battery charger IC designed for 2-cell packs with an 8.4V termination voltage. It handles a maximum charge current of 4A and accepts input supplies up to 32V, making it a fit for 12V or 24V automotive and industrial systems where the rail can spike. The junction temperature range spans -40°C to 125°C, so it can live under the hood or in an outdoor enclosure without derating headaches. Fault protection covers over-temperature, and you can program the charge current and a safety timer via external resistors.
4A charge current and thermal reality
At 4A, the 36-QFN with exposed pad needs a solid thermal via stitch to the ground plane — without it, junction temperature climbs fast. The 32V input ceiling covers automotive load-dump transients if you add a TVS clamp ahead of the IC; the part itself won't survive a direct 60V dump. The 8.4V pack voltage is fixed, not adjustable, so confirm your 2-cell Li-Ion stack matches that termination point — some cells top at 8.4V, others at 8.7V.
Lifecycle and sourcing
For dual-sourcing, the LT3650EMSE-8.4#PBF is a close functional sibling — same 2-cell 8.4V chemistry and 4A capability — but in an MSOP-12 package with a narrower -40°C to 85°C ambient range, so it won't match the full 125°C junction rating of this QFN part. The LT3650EDD-8.4#PBF is another 2-cell option in a 12-DFN, again with the 85°C ceiling. If you need the wide temperature grade, stick with the LT3651EUHE-8.4#PBF.