Datasheet LM2734 (Texas Instruments) - 9

LM2734 www.ti.com
SNVS288J – SEPTEMBER 2004 – REVISED DECEMBER 2014
7.2 Functional Block Diagram
VIN VIN Current-Sense Amplifier R Internal SENSE EN + Regulator ON and - C D2 IN Enable Thermal OFF Circuit Shutdown BOOST VBOOST Under Voltage Output C Lockout Driver 0.3: BOOST Current Control Switch SW L V Limit Logic SW VOUT OVP D I Oscillator L Comparator Reset 1 COUT Pulse - 0.88V + + PWM - R + - Comparator 1 ISENSE FB + Internal - + Compensation + Error R Signal + VREF 2 Corrective Ramp Error Amplifier - 0.8V GND
7.3 Feature Description 7.3.1 Output Overvoltage Protection
The overvoltage comparator compares the FB pin voltage to a voltage that is 10% higher than the internal reference Vref. Once the FB pin voltage goes 10% above the internal reference, the internal NMOS control switch is turned off, which allows the output voltage to decrease toward regulation.
7.3.2 Undervoltage Lockout
Undervoltage lockout (UVLO) prevents the LM2734 from operating until the input voltage exceeds 2.74 V (typical). The UVLO threshold has approximately 440 mV of hysteresis, so the part will operate until VIN drops below 2.3 V (typical). Hysteresis prevents the part from turning off during power up if VIN is nonmonotonic.
7.3.3 Current Limit
The LM2734 device uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a current limit comparator detects if the output switch current exceeds 1.7 A (typical), and turns off the switch until the next switching cycle begins.
7.3.4 Thermal Shutdown
Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature exceeds 165°C. After thermal shutdown occurs, the output switch does not turn on until the junction temperature drops to approximately 150°C. Copyright © 2004–2014, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM2734 Document Outline 1 Features 2 Applications 3 Description Table of Contents 4 Revision History 5 Pin Configuration and Functions 6 Specifications 6.1 Absolute Maximum Ratings 6.2 ESD Ratings 6.3 Recommended Operating Conditions 6.4 Thermal Information 6.5 Electrical Characteristics 6.6 Typical Performance Characteristics 7 Detailed Description 7.1 Overview 7.2 Functional Block Diagram 7.3 Feature Description 7.3.1 Output Overvoltage Protection 7.3.2 Undervoltage Lockout 7.3.3 Current Limit 7.3.4 Thermal Shutdown 7.4 Device Functional Modes 7.4.1 Enable Pin / Shutdown Mode 7.4.2 Soft-Start 8 Application and Implementation 8.1 Application Information 8.1.1 Boost Function 8.2 Typical Applications 8.2.1 LM2734X (1.6 MHz) VBOOST Derived from VIN 5V to 1.5 V/1 A 8.2.1.1 Design Requirements 8.2.1.2 Detailed Design Procedure 8.2.1.3 Application Curves 8.2.2 LM2734X (1.6 MHz) VBOOST Derived from VOUT 12 V to 3.3 V /1 A 8.2.2.1 Design Requirements 8.2.2.2 Detailed Design Procedure 8.2.2.3 Application Curves 8.2.3 LM2734X (1.6 MHz) VBOOST Derived from VSHUNT 18 V to 1.5 V /1 A 8.2.3.1 Design Requirements 8.2.3.2 Detailed Design Procedure 8.2.3.3 Application Curves 8.2.4 LM2734X (1.6 MHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 1 A 8.2.4.1 Design Requirements 8.2.4.2 Detailed Design Procedure 8.2.4.3 Application Curves 8.2.5 LM2734X (1.6 MHz) VBOOST Derived from Series Zener Diode (VOUT) 15 V to 9 V /1 A 8.2.5.1 Design Requirements 8.2.5.2 Detailed Design Procedure 8.2.5.3 Application Curves 8.2.6 LM2734Y (550 kHz) VBOOST Derived from VIN 5 V to 1.5 V / 1 A 8.2.6.1 Design Requirements 8.2.6.2 Detailed Design Procedure 8.2.6.3 Application Curves 8.2.7 LM2734Y (550 kHz) VBOOST Derived from VOUT 12 V to 3.3 V / 1 A 8.2.7.1 Design Requirements 8.2.7.2 Detailed Design Procedure 8.2.7.3 Application Curves 8.2.8 LM2734Y (550 kHz) VBOOST Derived from VSHUNT 18 V to 1.5 V / 1 A 8.2.8.1 Design Requirements 8.2.8.2 Detailed Design Procedure 8.2.8.3 Application Curves 8.2.9 LM2734Y (550 kHz) VBOOST Derived from Series Zener Diode (VIN) 15 V to 1.5 V / 1 A 8.2.9.1 Design Requirements 8.2.9.2 Detailed Design Procedure 8.2.9.3 Application Curves 8.2.10 LM2734Y (550 kHz) VBOOST Derived from Series Zener Diode (VOUT) 15 V to 9 V / 1 A 8.2.10.1 Design Requirements 8.2.10.2 Detailed Design Procedure 8.2.10.3 Application Curves 9 Power Supply Recommendations 10 Layout 10.1 Layout Guidelines 10.2 Layout Example 11 Device and Documentation Support 11.1 Third-Party Products Disclaimer 11.2 Trademarks 11.3 Electrostatic Discharge Caution 11.4 Glossary 12 Mechanical, Packaging, and Orderable Information