Dual-phase synchronous buck controller for 4V to 38V rails
The LTC3857EGN-1#PBF is a dual-output, dual-phase synchronous step-down DC/DC controller from Analog Devices' PolyPhase® series. It drives two independent buck rails or a single rail with interleaved phases, using an external transistor driver output. The controller accepts a 4V to 38V supply range and delivers a positive output configuration with synchronous rectification for efficiency above 95% in typical designs.
Switching frequency and timing flexibility
The switching frequency is programmable from 105kHz to 835kHz, with a secondary range of 350kHz to 535kHz selectable via the frequency control pin. This lets the designer trade off inductor size against switching losses — lower frequencies suit noise-sensitive audio or high-step-ratio rails, while higher frequencies shrink magnetics for space-constrained boards. The maximum duty cycle of 99.4% supports very low dropout operation, useful when the input rail sags close to the output target.
Temperature grade and environment
Rated for -40°C to 125°C junction temperature, this controller fits industrial motor drives, automotive under-hood power supplies, base-station line cards, and any environment where the ambient exceeds 85°C. The 28-SSOP package (0.154" body width) keeps the board footprint compact, but the thermal pad (exposed on the bottom) must be soldered to a copper plane — without it, junction temperature rises quickly above 85°C ambient at full load.
Control features for sequencing and protection
Built-in control features include an enable pin for sequencing, soft-start to limit inrush, power-good output for rail monitoring, and output voltage tracking for supply-rail sequencing in multi-rail systems. The tracking function allows the second output to follow the first during startup and shutdown — critical for FPGA and SoC core voltages that must not lag the I/O rail.
Lifecycle and compliance
It is ROHS3 compliant (lead-free), so it meets the EU RoHS exemption-free standard. No end-of-life notice or last-time-buy window has been announced — this part is a safe selection for new designs and ongoing production.
Sourcing and availability
This part is sourced through independent distribution and quoted to order against an RFQ. For urgent BOM fills, we can source from multiple inventory partners.