ZHCSFE2A August 2016 – November 2017 LM5161-Q1
PRODUCTION DATA.
- 1 特性
- 2 应用
- 3 说明
- 4 修订历史记录
- 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
- 7.3.12 Ripple Configuration
- 7.4 Device Functional Modes
-
8 Applications and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1
LM5161-Q1 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-Q1 Isolated Fly-Buck (36-V to 72-V Input, 12-V, 12-W Isolated Output)
- 8.2.1
LM5161-Q1 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器件和文档支持
- 12机械、封装和可订购信息
8.2.1.2.6 Series Ripple Resistor - RESR (FPWM = 1)
If the FPWM = 1, i.e. the FPWM pin is pulled high as when connected to VCC, a series resistor in series with the output capacitor or the external ripple injection circuit must be selected such that sufficient ripple injection (> 25mV) is ensured at the feedback pin FB. The ripple produced by RESR is proportional to the inductor current ripple, and therefore, RESR should be chosen for minimum inductor current ripple which occurs at minimum input voltage. The RESR is calculated by Equation 17.
With VO = 12 V, VREF = 2 V and ΔIL, min = 81 mA (at VIN, min= 15 V) as calculated in Equation 14, Equation 17 requires an RESR greater than or equal to 1.87 Ω. Selecting R4 (RESR) = 2 Ω results in approximately 700 mV of maximum output voltage ripple at VIN,max. However due to the internal DC Error correction loop, the load and line regulation will be much improved, despite the addition of a large RESR in the circuit. For applications which require even lower output voltage ripple, Type 2 or Type 3 ripple injection circuits must be used, as described inRipple Configuration. In this design example, with the FPWM =1 (i.e. the FPWM pin is pulled up to VCC) a 0 Ω ESR resistor is selected and the external Type 3 ripple injection circuit is used.