40V boost with 150°C junction — the under-hood power rail
The LT8338JMSE#PBF is an automotive-grade (AEC-Q100) step-up DC-DC converter from Analog Devices, delivering up to 1.2A from a 3V to 40V input rail. The 40V output ceiling and 150°C junction rating put it squarely in engine-bay or transmission-control power supplies where the ambient sees 105°C and the bus sees cold-crank dips to 3V. Synchronous rectification keeps efficiency above 90% across most of the load range — the internal FET replaces the usual catch diode, which matters when the board is sealed in a potting compound and every watt of dissipation has to conduct through the 10-MSOP-EP exposed pad.
Switching frequency and inductor selection
The oscillator runs from 300 kHz to 3 MHz, set by a single resistor. At 2 MHz the inductor drops to a 2.2 µH footprint — small enough for a 10 mm × 10 mm total solution — but the switching losses climb with frequency. For a 12 V input to 24 V output at 500 mA, 1 MHz is the sweet spot: the inductor is 4.7 µH and the efficiency stays above 92%. The 1.2A current limit is a peak switch limit, not a DC output limit. At high step-up ratios (5 V in to 40 V out) the average output current is lower than 1.2A by the duty cycle — roughly 150 mA at the highest ratio. The datasheet's efficiency curves show the real output capability for each VIN/VOUT pair.
Thermal and layout — the exposed pad is the heatsink
The 10-MSOP-EP package has a 3 mm × 3 mm exposed pad on the bottom. Solder that pad to a copper plane on the top layer with at least four vias into the internal ground plane — the thermal resistance from junction to ambient drops from 60°C/W with minimal copper to about 40°C/W with a 1 in² pour. Without that thermal via array, the 150°C junction rating is academic above 85°C ambient. Input and output capacitors should sit within 5 mm of the IC pins. The boost topology draws pulsed current from the input — a 10 µF ceramic at the VIN pin keeps the input ripple below 100 mV at 1.2A switching.
Lifecycle and compliance — active, no PCN watch needed
No pin-compatible second source exists for this exact part. The closest functional alternative is the LT8338IMS8E#PBF in the 8-MSOP-EP package — same boost controller core but with a different pinout and lower 1A current limit. A board spin is required to swap.