ZHCSN09A June 2021 – September 2022 LM5168-Q1 , LM5169-Q1
PRODUCTION DATA
- 1 特性
- 2 應用
- 3 說明
- 4 Revision History
- 5 Device Comparison Table
- 6 Pin Configuration and Functions
- 7 Specifications
-
8 Detailed Description
- 8.1 Overview
- 8.2 Functional Block Diagram
- 8.3
Feature Description
- 8.3.1 Control Architecture
- 8.3.2 Internal VCC Regulator and Bootstrap Capacitor
- 8.3.3 Internal Soft Start
- 8.3.4 On-Time Generator
- 8.3.5 Current Limit
- 8.3.6 N-Channel Buck Switch and Driver
- 8.3.7 Synchronous Rectifier
- 8.3.8 Enable, Undervoltage Lockout (EN/UVLO)
- 8.3.9 Power Good (PGOOD)
- 8.3.10 Thermal Protection
- 8.4 Device Functional Modes
-
9 Application and Implementation
- 9.1 Application Information
- 9.2
Typical Fly-Buck? Converter Application
- 9.2.1 Design Requirements
- 9.2.2
Detailed Design Procedure
- 9.2.2.1 Switching Frequency (RT)
- 9.2.2.2 Transformer Selection
- 9.2.2.3 Output Capacitor Selection
- 9.2.2.4 Secondary Output Diode
- 9.2.2.5 Setting Output Voltage
- 9.2.2.6 Input Capacitor
- 9.2.2.7 Type-3 Ripple Network
- 9.2.2.8 CBST Selection
- 9.2.2.9 Minimum Secondary Output Load
- 9.2.2.10 Example Design Summary
- 9.2.3 Application Curves
- 9.3 Typical Buck Application
- 9.4 Power Supply Recommendations
- 9.5 Layout
- 10Device and Documentation Support
- 11Mechanical, Packaging, and Orderable Information
9.4 Power Supply Recommendations
The LM516x-Q1 buck converter is designed to operate from a wide input voltage range between 6 V and 115 V. The characteristics of the input supply must be compatible with the Absolute Maximum Ratings and Recommended Operating Conditions tables. In addition, the input supply must be capable of delivering the required input current to the fully loaded regulator. Use Equation 36 to estimate the average input current.
where
- η = efficiency
If the converter is connected to an input supply through long wires or PCB traces with a large impedance, the parasitic inductance and resistance of the input cables can have an adverse affect on converter operation. The parasitic inductance in combination with the low-ESR ceramic input capacitors form an under-damped resonant circuit. This circuit can cause overvoltage transients at VIN each time the input supply is cycled ON and OFF. The parasitic resistance causes the input voltage to dip during a load transient. If the converter is operating close to the minimum input voltage, this dip can cause false UVLO fault triggering and a system reset. The best way to solve such issues is to reduce the distance from the input supply to the regulator and use an aluminum electrolytic input capacitor in parallel with the ceramics. The moderate ESR of the electrolytic capacitor helps to damp the input resonant circuit and reduce any voltage overshoots. A 10-μF electrolytic capacitor with a typical ESR of 0.5 Ω provides enough damping for most input circuit configurations.
An EMI input filter is often used in front of the regulator that, unless carefully designed, can lead to instability as well as some of the effects mentioned above. The Simple Success with Conducted EMI for DC-DC Converters Application Report provides helpful suggestions when designing an input filter for any switching regulator.