2-phase buck controller for high-current rails
The LTC3857EUH#TRPBF is a PolyPhase step-down switching regulator controller from Analog Devices, designed to drive two independent synchronous buck channels with interleaved phase timing. It operates from a 4V to 38V supply rail and delivers a positive output configuration with up to 99.4% duty cycle, making it suitable for intermediate bus conversion and high-current point-of-load regulation in industrial, automotive, and telecom equipment.
Switching frequency and inductor sizing
The switching frequency is programmable across two ranges: 105kHz to 835kHz and 350kHz to 535kHz. The lower range suits designs prioritising efficiency and thermal margin; the upper range shrinks the magnetics but increases switching losses. The wide spread lets you balance inductor size against dissipation without changing the controller.
Synchronous rectification and duty cycle headroom
Synchronous rectification is built in, so the external low-side FET replaces the catch diode — expect efficiency gains above 90% at moderate loads. The 99.4% maximum duty cycle keeps the output regulated through input sags, useful when the supply bus droops during cranking or brownout.
Control features for sequencing and fault handling
The controller integrates current limit, enable, frequency control, phase control, power good, soft start, and output tracking. Phase control lets you set the interleaving angle between the two channels, reducing input ripple current. Power good and tracking simplify rail sequencing in multi-voltage designs.
Package and thermal considerations
Housed in a 32-WFQFN with exposed pad (5x5 mm), the part relies on the PCB land pattern and via array under the pad to pull heat out of the junction. The operating junction temperature range is -40°C to 125°C, covering industrial and automotive under-hood environments. Surface-mount assembly is standard; the exposed pad must be soldered to a thermal plane.
Lifecycle and sourcing
The LTC3857EUH#TRPBF is listed as Active with ROHS3 compliance.