ZHCSEQ3D February 2016 – December 2022 LM5165
PRODUCTION DATA
- 1 特性
- 2 應用
- 3 說明
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
-
7 Detailed Description
- 7.1 Overview
- 7.2 Functional Block Diagram
- 7.3
Feature Description
- 7.3.1 Integrated Power MOSFETs
- 7.3.2 Selectable PFM or COT Mode Converter Operation
- 7.3.3 COT Mode Light-Load Operation
- 7.3.4 Low Dropout Operation and 100% Duty Cycle Mode
- 7.3.5 Adjustable Output Voltage (FB)
- 7.3.6 Adjustable Current Limit
- 7.3.7 Precision Enable (EN) and Hysteresis (HYS)
- 7.3.8 Power Good (PGOOD)
- 7.3.9 Configurable Soft Start (SS)
- 7.3.10 Thermal Shutdown
- 7.4 Device Functional Modes
-
8 Applications and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1 Design 1: Wide VIN, Low IQ COT Converter Rated at 5 V, 150 mA
- 8.2.2 Design 2: Small Solution Size PFM Converter Rated at 3.3 V, 50 mA
- 8.2.3 Design 3: High Density 12-V, 75-mA PFM Converter
- 8.2.4 Design 4: 3.3-V, 150-mA COT Converter With High Efficiency
- 8.2.5 Design 5: 15-V, 150-mA, 600-kHz COT Converter
- 8.3 Power Supply Recommendations
- 8.4 Layout
- 9 Device and Documentation Support
- 10Mechanical, Packaging, and Orderable Information
7.3.4 Low Dropout Operation and 100% Duty Cycle Mode
If RDSON1 and RDSON2 are the high-side and low-side MOSFET on-state resistances, respectively, and RDCR is the inductor DC resistance, the duty cycle in COT (CCM) or PFM mode is given by Equation 3.
The LM5165 offers a low input voltage to output voltage dropout by engaging the high-side MOSFET at 100% duty cycle. In COT mode, a frequency foldback feature effectively extends maximum duty cycle to 100% during low dropout conditions or load-on transients. Based on the 4-mV FB comparator dropout hysteresis, the duty cycle extends as needed at low input voltage conditions, corresponding to lower switching frequency. The PWM on-time extends based on the requirement that the FB voltage exceeds the dropout hysteresis during a given on-time. 100% duty cycle operation is eventually reached as the input voltage decreases towards the output setpoint. The output voltage stays in regulation at a lower supply voltage, thus achieving an extremely low dropout voltage.
Note that PFM mode operation provides an inherently natural transition to 100% duty cycle if needed for low dropout applications.
Use Equation 4 to calculate the minimum input voltage to maintain output regulation.
