SNVSCU3 October 2025 LM5137
PRODMIX
- 1
- 1 Features
- 2 Applications
- 3 Description
- 4 Related Products
- 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 Input Voltage Range (VIN)
- 7.3.2 Bias Supply Regulator (VCC, BIAS1/VOUT1, VDDA)
- 7.3.3 Precision Enable (EN1, EN2)
- 7.3.4 Switching Frequency (RT)
- 7.3.5 Pulse Frequency Modulation and Synchronization (PFM/SYNC)
- 7.3.6 Synchronization Out (SYNCOUT)
- 7.3.7 Dual Random Spread Spectrum (DRSS)
- 7.3.8 Configurable Soft Start (RSS)
- 7.3.9 Output Voltage Setpoints (FB1, FB2)
- 7.3.10 Error Amplifier and PWM Comparator (FB1, FB2, COMP1, COMP2)
- 7.3.11 Inductor Current Sense (ISNS1+, BIAS1/VOUT1, ISNS2+, VOUT2)
- 7.3.12 Minimum Controllable On-Time
- 7.3.13 100% Duty Cycle Capability
- 7.3.14 MOSFET Gate Drivers (HO1, HO2, LO1, LO2)
- 7.3.15 Output Configurations (CNFG)
- 7.4 Device Functional Modes
-
8 Application and Implementation
- 8.1 Application Information
- 8.2
Typical Applications
- 8.2.1
Design 1 – Dual 5V and 3.3V, 20A Buck Regulator for 12V
Input Applications
- 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 Custom Design With Excel Quickstart Tool
- 8.2.1.2.3 Inductor Calculations
- 8.2.1.2.4 Shunt Resistors
- 8.2.1.2.5 Ceramic Output Capacitors
- 8.2.1.2.6 Ceramic Input Capacitors
- 8.2.1.2.7 Feedback Resistors
- 8.2.1.2.8 Input Voltage UVLO Resistors
- 8.2.1.2.9 Compensation Components
- 8.2.1.3 Application Curves
- 8.2.2 Design 2 – Two-Phase, Single-Output Synchronous Buck Regulator
- 8.2.3 Design 3 – 12V, 20A, 400kHz, Two-Phase Buck Regulator for 48V Server Applications
- 8.2.1
Design 1 – Dual 5V and 3.3V, 20A Buck Regulator for 12V
Input Applications
- 8.3 Power Supply Recommendations
- 8.4 Layout
- 9 Device and Documentation Support
- 10Revision History
- 11Mechanical, Packaging, and Orderable Information
8.1.1.2 Buck Inductor
For most applications, choose a buck inductance such that the inductor ripple current, ΔIL, is between 30% and 50% of the maximum DC output current at nominal input voltage. Choose the inductance using Equation 11 based on a peak inductor current given by Equation 12.
Check the inductor data sheet to make sure that the saturation current rating is well above the peak inductor current of a particular design. Ferrite-cored inductors have very low core loss and are preferred at high switching frequencies, so design goals can then concentrate on copper loss and preventing saturation. Low inductor core loss is evidenced by reduced no-load input current and higher light-load efficiency. However, ferrite core materials exhibit a hard saturation characteristic where the inductance collapses abruptly when the saturation current is exceeded. This action results in an outsized increase in inductor ripple current and higher output voltage ripple, not to mention reduced efficiency and compromised reliability. Note that the saturation current rating of an inductor generally decreases as the core temperature increases. Of course, accurate overcurrent protection is critical to avoiding inductor saturation.