Monolithic flyback with a 100 V input ceiling
The LT8300IS5#TRMPBF is a monolithic flyback switching regulator from Analog Devices, packing the power switch, control logic, and compensation into a 5-pin TSOT-23-5 package. It handles input voltages from 6 V up to 100 V, which means it can run off rectified 48 V telecom rails or 72 V industrial buses without an external pre-regulator — a common headache in isolated bias supply designs. Rated for 260 mA output current, this part is sized for auxiliary rails: IGBT gate-drive supplies, isolated sensor transceivers, or the housekeeping rail in a motor drive. The 260 mA figure is the maximum switch current limit; the actual deliverable load depends on the transformer turns ratio and switching frequency, but it's a solid fit for the 100-200 mA range most isolated bias circuits need.
This is a true flyback converter, not a simple buck-boost. The transformer serves as both the energy-storage inductor and the isolation barrier. The output can be configured as positive or negative, and the flyback action inherently provides galvanic isolation when you use a transformer with separate primary and secondary windings — no optocoupler needed for the feedback loop on many designs. The switching frequency is programmable from 7.5 kHz to 750 kHz via a single resistor. Running at the low end reduces switching losses and improves cross-regulation for multi-output windings; the high end shrinks the transformer core size. The trade-off is that at 750 kHz the internal switch losses and snubber dissipation climb, so the 260 mA limit may need derating above 85°C ambient. There is no synchronous rectifier on the secondary side — the output diode handles the current. A Schottky diode with a low Vf is recommended for the secondary rectifier to keep losses manageable.
Package reality — TSOT-23-5 thermal limits
The LT8300 comes in a 5-lead TSOT-23-5 package — about 2.9 mm × 2.8 mm with a 0.95 mm pin pitch. The exposed pad on the bottom is the GND slug and the primary heat path. A solid copper pour under the part, connected to the ground plane with at least four vias, is essential to keep the junction temperature below the 125°C absolute maximum at full load in a 70°C ambient. The package is offered in Tape & Reel (TR) for production reels and Cut Tape (CT) for prototype quantities. The TR suffix in the order code means it ships on a 7-inch reel, typically 2,500 pieces per reel for this TSOT package.
It remains a current-design part suitable for new production builds. The RoHS3 compliance means no exempted lead in the solder finish, so it ships clean for EU markets without a RoHS waiver. The operating temperature range covers -40°C to 125°C junction temperature, which qualifies it for industrial environments — motor drives, power supplies, and telecom equipment where the ambient can hit 85°C with internal heating.