SNVS574G
July 2008 – July 2019
LM3421
,
LM3423
PRODUCTION DATA.
1
Features
2
Applications
3
Description
Device Images
Typical Boost Application
4
Revision History
5
Device Comparison
6
Pin Configuration and Functions
Pin Functions
7
Specifications
7.1
Absolute Maximum Ratings
7.2
ESD Ratings
7.3
Recommended Operating Conditions
7.4
Thermal Information
7.5
Electrical Characteristics
7.6
Typical Characteristics
8
Detailed Description
8.1
Overview
8.2
Functional Block Diagram
8.3
Feature Description
8.3.1
Current Regulators
8.3.2
Predictive Off-Time (PRO) Control
8.3.3
Average LED Current
8.3.4
Analog Dimming
8.3.5
Current Sense and Current Limit
8.3.6
Overcurrent Protection
8.3.7
Zero Current Shutdown
8.3.8
Control Loop Compensation
8.3.9
Start-Up Regulator
8.3.10
Overvoltage Lockout (OVLO)
8.3.11
Input Undervoltage Lockout (UVLO)
8.3.11.1
UVLO Only
8.3.11.2
PWM Dimming and UVLO
8.3.12
PWM Dimming
8.3.13
LM3423 Only: DPOL, FLT, TIMR, and LRDY
9
Application and Implementation
9.1
Application Information
9.1.1
Inductor
9.1.2
LED Dynamic Resistance
9.1.3
Output Capacitor
9.1.4
Input Capacitors
9.1.5
Main MOSFET / Dimming MOSFET
9.1.6
Re-Circulating Diode
9.1.7
Boost Inrush Current
9.1.8
Switching Frequency
9.2
Typical Applications
9.2.1
Basic Topology Schematics
9.2.1.1
Design Requirements
9.2.1.2
Detailed Design Procedure
9.2.1.2.1
Operating Point
9.2.1.2.2
Switching Frequency
9.2.1.2.3
Average LED Current
9.2.1.2.4
Inductor Ripple Current
9.2.1.2.5
LED Ripple Current
9.2.1.2.6
Peak Current Limit
9.2.1.2.7
Loop Compensation
9.2.1.2.8
Input Capacitance
9.2.1.2.9
N-channel FET
9.2.1.2.9.1
Boost and Buck-Boost
9.2.1.2.10
Diode
9.2.1.2.11
Output OVLO
9.2.1.2.12
Input UVLO
9.2.1.2.13
PWM Dimming Method
9.2.1.2.14
Analog Dimming Method
9.2.2
LM3421 Buck-Boost Application
9.2.2.1
Design Requirements
9.2.2.2
Detailed Design Procedure
9.2.2.2.1
Operating Point
9.2.2.2.2
Switching Frequency
9.2.2.2.3
Average LED Current
9.2.2.2.4
Inductor Ripple Current
9.2.2.2.5
Output Capacitance
9.2.2.2.6
Peak Current Limit
9.2.2.2.7
Loop Compensation
9.2.2.2.8
Input Capacitance
9.2.2.2.9
N-channel FET
9.2.2.2.10
Diode
9.2.2.2.11
Input UVLO
9.2.2.2.12
Output OVLO
9.2.2.3
Application Curve
9.2.3
LM3421 BOOST Application
9.2.3.1
Design Requirements
9.2.3.2
Detailed Design Procedure
9.2.4
LM3421 Buck-Boost Application
9.2.4.1
Design Requirements
9.2.4.2
Detailed Design Procedure
9.2.5
LM3423 Boost Application
9.2.5.1
Design Requirements
9.2.5.2
Detailed Design Procedure
9.2.6
LM3421 Buck-Boost Application
9.2.6.1
Design Requirements
9.2.6.2
Detailed Design Procedure
9.2.7
LM3423 Buck Application
9.2.7.1
Design Requirements
9.2.7.2
Detailed Design Procedure
9.2.8
LM3423 Buck-Boost Application
9.2.8.1
Design Requirements
9.2.8.2
Detailed Design Procedure
9.2.9
LM3421 SEPIC Application
9.2.9.1
Design Procedure
9.2.9.2
Detailed Design Procedure
10
Power Supply Recommendations
10.1
General Recommendations
10.2
Input Supply Current Limit
11
Layout
11.1
Layout Guidelines
11.2
Layout Example
12
Device and Documentation Support
12.1
Device Support
12.1.1
Third-Party Products Disclaimer
12.2
Related Links
12.3
Community Resources
12.4
Trademarks
12.5
Electrostatic Discharge Caution
12.6
Glossary
13
Mechanical, Packaging, and Orderable Information
Package Options
Mechanical Data (Package|Pins)
PWP|20
MHTS001G
Thermal pad, mechanical data (Package|Pins)
PWP|20
PPTD289
Orderable Information
snvs574g_oa
snvs574g_pm
9.2.2.3
Application Curve
V
OUT
= 21 V
Figure 37.
Sample Buck-Boost Efficiency vs Input Voltage.