1 Features
1• Wide Input Voltage Range of 3 V to 65 V
• 9.7-μA No-Load Quiescent Current
• –40°C to 150°C Junction Temperature Range
• Fixed (3.3-V, 5-V) or Adjustable VOUT Options
• Meets EN55022 / CISPR 22 EMI Standards
• Integrated 1-Ω PFET Buck Switch
– Supports 100% Duty Cycle for Low Dropout
• Integrated 0.5-Ω NFET Synchronous Rectifier
– Eliminates External Schottky Diode
• Programmable Peak Current Limit Supports:
– 500-mA, 300-mA, or 200-mA Loads
• Selectable PFM or COT Mode Operation
• 1.223-V ±1.2% Internal Voltage Reference
• Switching Frequency up to 600 kHz
• 900-μs Internal or Externally-Adjustable Soft Start
• Diode Emulation and Pulse Skipping for Ultra-
High Light-Load Efficiency
• No Loop Compensation or Bootstrap Components
• Precision Enable and Input UVLO With Hysteresis
• Open-Drain Power Good Indicator
• Thermal Shutdown Protection With Hysteresis
• Pin-to-Pin Compatible With the LM5165
• 10-Pin, 3-mm × 3-mm VSON Package
• Create a Custom Regulator Design Using
WEBENCH® Power Designer

2 Applications
• Factory and Building Automation
• Automotive and Battery-Powered Applications
• High Voltage LDO Replacement
• Low Power Bias Supplies

3 Description
The LM5166 is a compact, easy-to-use, 3-V to 65-V,
ultra-low IQ synchronous buck converter with high
efficiency over wide input voltage and load current
ranges. With integrated high-side and low-side power
MOSFETs, up to 500 mA of output current can be
delivered at fixed output voltages of 3.3 V or 5 V, or
an adjustable output. The converter is designed to
simplify implementation while providing options to
optimize the performance for the target application.
Pulse frequency modulation (PFM) mode is selected
for optimal light-load efficiency or constant on-time
(COT) control for nearly constant operating
frequency. Both control schemes do not require loop
compensation while providing excellent line and load
transient response and short PWM on-time for large
step-down conversion ratios.
The high-side P-channel MOSFET can operate at
100% duty cycle for lowest dropout voltage and does
not require a bootstrap capacitor for gate drive. Also,
the current limit setpoint is adjustable to optimize
inductor selection for a particular load current
requirement. Selectable and adjustable start-up
timing options include minimum delay (no soft start),
internally fixed (900 μs), and externally programmable
soft start using a capacitor. An open-drain PGOOD
indicator can be used for sequencing, fault reporting,
and output voltage monitoring. The LM5166 is
available in a 10-pin VSON package with 0.5-mm pin
pitch.