Synchronous buck controller with wide input range
The LTC3851AEUD-1#PBF is a single-phase synchronous buck controller from Analog Devices, designed for step-down conversion from input rails spanning 4V to 38V (Vcc/Vdd). The 99% maximum duty cycle means it can run near dropout — useful when the input sags close to the output target, like in battery-backed systems where the bus voltage decays under load. Switching frequency is programmable from 235kHz to 750kHz via a resistor on the RT pin. The lower end suits designs prioritising efficiency (lower FET gate-charge losses), while the upper end shrinks the inductor and output capacitor footprint. There is no clock-sync input on this variant — the -1 suffix omits that feature, so if you need external synchronisation to a system clock, look at the LTC3851EUFD or similar parts with SYNC capability.
Package, thermal, and board-fit
Housed in a 16-lead WFQFN with exposed pad (3x3 mm body, supplier device package 16-QFN). The 0.5 mm pitch QFN demands careful solder-paste stencil design; a 4-layer board with thermal vias under the pad is standard practice for this package class. Control features include Enable, Frequency Control, Power Good, Soft Start, and Tracking. The tracking input lets the output voltage follow an external ramp during startup — useful for sequencing multiple rails in an FPGA or SoC power tree. Output configuration is positive, and the transistor driver output drives external N-channel MOSFETs in a synchronous rectifier topology.