**Description** The LM25019 is a 48-V, 100-mA synchronous step-down regulator with integrated high-side and low-side MOSFETs. The constant on-time (COT) control scheme employed in the LM25019 requires no loop compensation, provides excellent transient response, and enables very high step-down ratios. The on-time varies inversely with the input voltage resulting in nearly constant frequency over the input voltage range. A high-voltage start-up regulator provides bias power for internal operation of the IC and for integrated gate drivers. A peak current limit circuit protects against overload conditions. The undervoltage lockout (UVLO) circuit allows the input undervoltage threshold and hysteresis to be independently programmed. Other protection features include thermal shutdown and bias supply undervoltage lockout. **Features** Wide 7.5-V to 48-V Input Range Integrated 100-mA High-Side and Low-Side Switches No Schottky Required Constant On-Time Control No Loop Compensation Required Ultra-Fast Transient Response Nearly Constant Operating Frequency Intelligent Peak Current Limit Adjustable Output Voltage From 1.225 V Precision 2% Feedback Reference Frequency Adjustable to 1 MHz Adjustable Undervoltage Lockout Remote Shutdown Thermal Shutdown