ZHCSFE3B March 2016 – November 2017 LM5161
PRODUCTION DATA.
- 1 特性
- 2 應用
- 3 說明
- 4 修訂歷史記錄
- 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 Control Circuit
- 7.3.2 VCC Regulator
- 7.3.3 Regulation Comparator
- 7.3.4 Soft-Start
- 7.3.5 Error Transconductance (GM) Amplifier
- 7.3.6 On-Time Generator
- 7.3.7 Current Limit
- 7.3.8 N-Channel Buck Switch and Driver
- 7.3.9 Synchronous Rectifier
- 7.3.10 Enable / Undervoltage Lockout (EN/UVLO)
- 7.3.11 Thermal Protection
- 7.4 Device Functional Modes
-
8 Applications and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1
LM5161 Synchronous Buck (15-V to 95-V Input, 12-V Output, 1-A Load)
- 8.2.1.1 Design Requirements
- 8.2.1.2
Detailed Design Procedure
- 8.2.1.2.1 Custom Design With WEBENCH® Tools
- 8.2.1.2.2 Output Resistor Divider Selection
- 8.2.1.2.3 Frequency Selection
- 8.2.1.2.4 Inductor Selection
- 8.2.1.2.5 Output Capacitor Selection
- 8.2.1.2.6 Series Ripple Resistor - RESR (FPWM = 1)
- 8.2.1.2.7 VCC and Bootstrap Capacitor
- 8.2.1.2.8 Input Capacitor Selection
- 8.2.1.2.9 Soft-Start Capacitor Selection
- 8.2.1.2.10 EN/UVLO Resistor Selection
- 8.2.1.3 Application Curves
- 8.2.2 LM5161 Isolated Fly-Buck (36-V to 72-V Input, 12-V, 12-W Isolated Output)
- 8.2.3 Ripple Configuration
- 8.2.1
LM5161 Synchronous Buck (15-V to 95-V Input, 12-V Output, 1-A Load)
- 8.3 Do's and Don'ts
- 9 Power Supply Recommendations
- 10Layout
- 11器件和文檔支持
- 12機械、封裝和可訂購信息
8.2.1.2.4 Inductor Selection
The inductor is selected to limit the inductor ripple current to a value between 20 and 40 percent of the maximum load current. The minimum value of the inductor required in this application can be calculated from Equation 10:
Based on Equation 10 , the minimum value of the inductor is calculated to be 85 µH for VIN = 80-V (max) and inductor current ripple will be 40 percent of the maximum load current. Allowing some margin for inductance variation and inductor saturation, a higher standard value of L1 (L) = 100 µH is selected for this design.
The peak inductor current at maximum load must be smaller than the minimum current limit threshold of the high side FET as given inElectrical Characteristics table. The inductor current ripple at any input voltage is given by:
The peak-to-peak inductor current ripple is calculated to be 81 mA and 341 mA at the minimum and maximum input voltages respectively. The maximum peak inductor current in the buck FET is given by Equation 12:
In this design with maximum output current of 1-A, the maximum peak inductor current is calculated to be approximately 1.17 A at VIN,max = 80 V, which is less than the minimum high-side FET current limit threshold.
The saturation current of the inductor must also be carefully considered. The peak value of the inductor current will be bound by the high side FET current limit during overload or short circuit conditions. Based on the high side FET current limit specification in theElectrical Characteristics, an inductor with saturation current rating above 1.9 A (max) should be selected.