Buck controller with 100% duty cycle capability
The LTC1147LCS8#PBF: It operates from a 3.5V to 14V supply rail and delivers a transistor driver output for the external switch. A key feature for low-dropout operation is the 100% maximum duty cycle — the controller can keep the external switch on continuously, passing the input voltage straight to the output with minimal headroom. This matters when the input rail sags close to the target output voltage, such as in battery-powered systems near end-of-discharge. The controller does not include synchronous rectification, so the external MOSFET and a Schottky catch diode handle the switching cycle. This keeps the BOM simple and avoids the shoot-through risk of a complementary FET pair, at the cost of slightly higher diode conduction loss at high currents.
Supply range, temperature grade, and control
The input supply range (Vcc/Vdd) spans 3.5V to 14V, covering standard 5V and 12V rails as well as 3.6V lithium-ion battery packs. The single positive output is configured as a step-down regulator with current-limit and enable control features. It is not specified for automotive or extended industrial temperature operation. The controller uses current-mode architecture with the enable pin allowing the regulator to be shut down for power savings. The current-limit feature protects the external MOSFET and inductor during overload or startup into a pre-biased output.
8-SOIC package and surface-mount assembly
Housed in an 8-lead SOIC package (8-SOIC, 0.154" body width, 3.90mm pitch), the LTC1147LCS8#PBF is a surface-mount device supplied in tube packaging. The supplier device package is designated 8-SO. The SOIC-8 footprint is standard and widely supported by PCB layout tools. The narrow body width keeps the board footprint compact, suitable for space-constrained power sections on mixed-signal boards.