What this dual-phase buck controller brings to the board
The LTC3858EUH#PBF is a dual-output, 2-phase step-down DC/DC controller from Analog Devices' PolyPhase series. It drives external N-channel MOSFETs in a synchronous buck topology, delivering two independent regulated rails from a single 4V to 38V input. The 2-phase architecture interleaves the switching edges, reducing input ripple current and letting you use smaller input capacitors than a single-phase controller of equivalent output current. Switching frequency is programmable from 105kHz up to 835kHz, with a separate range of 350kHz to 535kHz available through the SYNC pin — useful for locking to an external clock or staying clear of sensitive frequency bands.
Temperature range and where it runs
Rated for -40°C to 125°C junction temperature, this part handles the thermal extremes you find in outdoor telecom enclosures, motor-drive cabinets, and under-hood automotive auxiliary supplies. The 32-QFN (5x5) package with exposed pad pulls heat into the PCB copper plane — make sure your layout includes a thermal via array under the pad to keep junction temperature inside the limit at full load.
Package and mounting
Current limit, enable, frequency control, power good, and soft start are all built in. The 99.4% maximum duty cycle means the controller can run near dropout — useful when the input rail sags and you need to keep the output up. Soft start limits inrush on both channels independently; the power-good output can sequence a downstream load or drive a reset line. No clock sync pin on this variant — if you need external synchronization, the LTC3890EUH#PBF adds that feature.
Package and mounting
Surface-mount in a 32-QFN (5x5) with exposed pad. The exposed pad is the primary thermal path and also carries the ground reference — ensure your PCB footprint has a matching thermal land with at least nine vias to an internal ground plane.