Datasheet LM2734 (Texas Instruments) - 10

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LM2734
SNVS288J – SEPTEMBER 2004 – REVISED DECEMBER 2014
www.ti.com 7.4 Device Functional Modes 7.4.1 Enable Pin / Shutdown Mode
The LM2734 device has a shutdown mode that is controlled by the enable pin (EN). When a logic low voltage is applied to EN, the part is in shutdown mode and its quiescent current drops to typically 30 nA. Switch leakage adds another 40 nA from the input supply. The voltage at this pin should never exceed VIN + 0.3 V.
7.4.2 Soft-Start
This function forces VOUT to increase at a controlled rate during start up. During soft-start, the error amplifier’s reference voltage ramps from 0 V to its nominal value of 0.8 V in approximately 200 µs. This forces the regulator output to ramp up in a more linear and controlled fashion, which helps reduce inrush current. Under some circumstances at start-up, an output voltage overshoot may still be observed. This may be due to a large output load applied during start up. Large amounts of output external capacitance can also increase output voltage overshoot. A simple solution is to add a feed forward capacitor with a value between 470 pf and 1000 pf across the top feedback resistor (R1). See Figure 23 for further detail. 10 Submit Documentation Feedback Copyright © 2004–2014, Texas Instruments Incorporated 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