Synchronous buck-boost controller for wide-input-rail designs
The Texas Instruments LM5176RHFT is a synchronous buck-boost switching regulator controller that regulates a positive output voltage from an input that can be above, below, or equal to the output. Its 4.2 V to 55 V supply range covers 12 V and 24 V industrial buses, automotive battery rails through cold-crank and load-dump, and multi-cell Li-ion battery packs without a cascaded pre-regulator. The controller drives an external transistor pair in a single-inductor, four-switch buck-boost topology with synchronous rectification, which maintains efficiency when the input voltage crosses the output regulation point. Switching frequency is programmable from 100 kHz to 600 kHz and includes a clock sync input for system-level EMI management. Control features on the 28-VFQFN (5x4 mm) package include current limit, enable, frequency control, power-good flag, and a programmable soft start.
Wide input range — what the 4.2 V to 55 V supply means for your rail budget
The 4.2 V minimum supply means this part regulates through the bottom of a 5 V rail during brownout and can run directly from a 4-cell Li-ion battery near its discharge floor. The 55 V maximum covers 24 V industrial rails with 20% tolerance plus transient spikes, and handles automotive 12 V system load-dump events without an external clamp. A buck-boost topology is the right choice when the input can swing both below and above the target output — a simple buck or boost alone would lose regulation at one end of the range.
The part is ROHS3 compliant per the current revision.
Package and thermal — 28-VFQFN with exposed pad
Without that stitch, junction temperature rises quickly when the external MOSFETs switch at high duty cycles.