SNVSB95 July 2019 LM3421-Q1 , LM3423-Q1
PRODUCTION DATA.
- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Device Comparison
- 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 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)
- 8.3.12 PWM Dimming
- 8.3.13 LM3423-Q1 Only: DPOL, FLT, TIMR, and LRDY
-
9 Application and Implementation
- 9.1 Application Information
- 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
- 9.2.1.2.10 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-Q1 BOOST Application
- 9.2.4 LM3421-Q1 Buck-Boost Application
- 9.2.5 LM3423-Q1 Boost Application
- 9.2.6 LM3421 Buck-Boost Application
- 9.2.7 LM3423 Buck Application
- 9.2.8 LM3423 Buck-Boost Application
- 9.2.9 LM3421 SEPIC Application
- 9.2.1
Basic Topology Schematics
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
9.2.2.2.12 Output OVLO
Solve for ROV2:
Equation 144. 
The closest standard resistor is 432 kΩ; therefore, VHYSO is:
Equation 145. 
Solve for ROV1:
Equation 146. 
The closest standard resistor is 13.7 kΩ, making VTURN-OFF:
Equation 147. 
The chosen components from step 12 are:
Equation 148. 
Table 2. Bill of Materials
| QTY | PART ID | PART VALUE | MANUFACTURER | PART NUMBER |
|---|---|---|---|---|
| 1 | LM3421 | Buck-boost controller | TI | LM3421MH |
| 1 | CBYP | 2.2-µF X7R 10% 16V | MURATA | GRM21BR71C225KA12L |
| 1 | CCMP | 0.33-µF X7R 10% 25V | MURATA | GRM21BR71E334KA01L |
| 1 | CFS | 0.27-µF X7R 10% 25V | MURATA | GRM21BR71E274KA01L |
| 4 | CIN | 4.7-µF X7R 10% 100V | TDK | C5750X7R2A475K |
| 4 | CO | 10-µF X7R 10% 50V | TDK | C4532X7R1H106K |
| 1 | COV | 47-pF COG/NPO 5% 50V | AVX | 08055A470JAT2A |
| 1 | CT | 1000-pF COG/NPO 5% 50V | MURATA | GRM2165C1H102JA01D |
| 1 | D1 | Schottky 100 V 12 A | VISHAY | 12CWQ10FNPBF |
| 1 | L1 | 33 µH 20% 6.3 A | COILCRAFT | MSS1278-333MLB |
| 1 | Q1 | NMOS 100 V 32 A | FAIRCHILD | FDD3682 |
| 1 | Q2 | PNP 150 V 600 mA | FAIRCHILD | MMBT5401 |
| 1 | RCSH | 12.4 kΩ 1% | VISHAY | CRCW080512K4FKEA |
| 1 | RFS | 10 Ω 1% | VISHAY | CRCW080510R0FKEA |
| 2 | RHSP, RHSN | 1 kΩ 1% | VISHAY | CRCW08051K00FKEA |
| 1 | RLIM | 0.04 Ω 1% 1 W | VISHAY | WSL2512R0400FEA |
| 1 | ROV1 | 13.7 kΩ 1% | VISHAY | CRCW080513K7FKEA |
| 1 | ROV2 | 432 kΩ 1% | VISHAY | CRCW0805432KFKEA |
| 1 | RSNS | 0.1 Ω 1% 1 W | VISHAY | WSL2512R1000FEA |
| 1 | RT | 49.9 kΩ 1% | VISHAY | CRCW080549K9FKEA |
| 1 | RUV1 | 18.2 kΩ 1% | VISHAY | CRCW080518K2FKEA |
| 1 | RUV2 | 130 kΩ 1% | VISHAY | CRCW0805130KFKEA |