Topology flexibility for non-isolated and isolated rails
The LM2586S-12 supports boost, flyback, and forward converter topologies from a single controller — a single BOM line covers both non-isolated step-up and galvanically isolated designs without a different PWM IC. The 3A switch current rating sets the power ceiling: a boost from 12V to 24V at 1.5A output is within reach; a flyback winding the same switch current into a 5V isolated rail at 2A is practical with a reasonable turns ratio.
4V to 40V input — wide enough for battery and industrial buses
The 4V minimum input lets the part start from a deeply discharged lithium-ion cell or a 5V rail with margin; the 40V maximum covers 24V industrial supplies with transients up to the abs-max rating without an external clamp. Switching frequency spans 100kHz to 200kHz — the lower end suits larger magnetics for higher efficiency, the upper end shrinks the transformer or inductor footprint at the cost of slightly higher switching losses.
Fixed 12V output and thermal package
Output is fixed at 12V — no external feedback divider needed, which saves two resistors and one feedback-node noise path. No synchronous rectifier is integrated — the external catch diode (a Schottky for boost, an ultra-fast diode for flyback) must be selected for the peak switch current and reverse voltage. The diode forward drop adds directly to the conduction loss.
Active production — legacy tin-lead finish
The TPS65261RHBT is a different part entirely — a triple-output buck regulator with synchronous rectification, not a boost/flyback controller. It is not a functional second-source for the LM2586S-12; the topologies and pinouts do not overlap.