What this part is and where it fits
The Texas Instruments UC3909QTR is a battery charge controller, designed to manage the charging profile for lead-acid or similar battery chemistries in a single IC. It handles the voltage and current regulation loop, charge termination, and status indication — essentially the brains of a smart charger. You will find this part in industrial power supplies, UPS systems, battery backup units, and any equipment where a sealed lead-acid battery needs a controlled charge cycle.
Lifecycle and compliance — the sourcing reality
The product status is Active. This part is RoHS non-compliant.
What the ratings mean for your BOM
As a charge controller, the UC3909QTR does not have a single headline rating like a voltage or current output — its value is in the control algorithm. It implements a multi-stage charge profile (bulk, absorption, float) and includes temperature compensation if you connect an external thermistor. That means the external pass transistor (typically a MOSFET or Darlington pair) and the current-sense resistor are what actually set the charge current and voltage; the UC3909QTR just drives the gate. For a BOM planner, that translates to: you need at least one power transistor, one sense resistor, and a few passive components to make it work. The controller itself draws minimal quiescent current, so the thermal design is about the pass element, not the IC.
Package and handling
The package is Bulk.