Flyback regulator with 42 V input ceiling
The LT8301HS5#TRMPBF is a monolithic flyback switching regulator from Analog Devices that integrates a 1.2 A power switch in a TSOT-23-5 package.
What the 1.2 A switch and flyback topology mean for your BOM
The 1.2 A current rating is the peak switch current limit, not the continuous output — in a flyback converter the output current depends on the turns ratio, duty cycle, and switching frequency. For a typical 5 V output from a 12 V input, expect around 300-400 mA continuous before the switch hits its limit. The topology supports positive or negative outputs with galvanic isolation using a coupled inductor or transformer, which is the key advantage over a simple buck-boost. Switching frequency goes down to 10 kHz — the part uses a Burst Mode operation that lowers the frequency at light loads to maintain efficiency. At 10 kHz the magnetics can be physically larger than a 500 kHz design, but the trade-off is lower switching losses and better efficiency under 10 mA loads. The junction temperature rating of -40°C to 150°C means the silicon is qualified for the full automotive temperature range, including the 125°C ambient often seen under the hood. The TSOT-23-5 package's thermal resistance limits the dissipation to about 0.8 W at 150°C junction in still air — the 1.2 A switch peak is only sustainable at low duty cycles or with adequate board copper.
It is ROHS3 compliant, meeting the current EU restriction on hazardous substances without exemptions.