The LM5145-Q1 75-V synchronous buck controller regulates from a high input voltage source or from an input rail subject to high-voltage transients, minimizing the need for external surge suppression components. A high-side switch minimum on-time of 40 ns gives large step-down ratios, enabling the direct step-down conversion from a 48-V nominal input to low-voltage rails for reduced system complexity and solution cost. The LM5145-Q1 continues to operate during input voltage dips as low as 5.5 V, at nearly 100% duty cycle if needed, making it an excellent choice for high-power automotive DC/DC regulators, automotive motor drives, and HEV/EV power compliant to LV-148. Forced-PWM (FPWM) operation eliminates switching frequency variation to minimize EMI, while user-selectable diode emulation lowers current consumption at light-load conditions. The adjustable switching frequency as high as 1 MHz can be synchronized to an external clock source to eliminate beat frequencies in noise-sensitive applications.