Step-Down DC-to-DC Controller ADP1821 FEATURES GENERAL DESCRIPTION Wide power-input voltage range: 1 V to 24 V The ADP1821 is a versatile and inexpensive, synchronous, Chip supply voltage range: 3.7 V to 5.5 V pulse-width-modulated (PWM), voltage-mode, step-down Wide output voltage range: 0.6 V to 85% of input voltage controller. It drives an all N-channel power stage to regulate an 1% accuracy, 0.6 V reference voltage output voltage as low as 0.6 V. The ADP1821 can be configured All N-channel MOSFET design for low cost to provide output voltages from 0.6 V to 85% of the input Fixed-frequency operation 300 kHz, 600 kHz, or voltage and is sized to handle large MOSFETs for point-of-load synchronized operation up to 1.2 MHz regulators. No current sense resistor required The ADP1821 is well suited for a wide range of high power Power-good output applications, such as DSP and processor core power in telecom- Programmable soft start with reverse current protection munications, medical imaging, high performance servers, and Soft start, thermal overload, current-limit protection industrial applications. It operates from a 3.7 V to 5.5 V supply Undervoltage lockout with a power input voltage ranging from 1.0 V to 24 V. 10 A shutdown supply current The ADP1821 operates at a pin-selectable, fixed switching Small, 16-lead QSOP frequency of either 300 kHz or 600 kHz, minimizing external APPLICATIONS component size and cost. For noise sensitive applications, it Telecommunications and networking systems can be synchronized to an external clock to achieve switching Set-top boxes frequencies between 300 kHz and 1.2 MHz. The ADP1821 Printers includes soft start protection to limit the inrush current from Servers the input supply during startup, reverse current protection Medical imaging systems during soft start for precharged outputs, as well as a unique Microprocessor and DSP core power supplies adjustable lossless current-limit scheme utilizing external Mobile communication base stations MOSFET sensing. The ADP1821 operates over the 40C to +125C junction temperature range and is available in a 16-lead QSOP. 97 BIAS INPUT T = 25C 5V A FREQUENCY = 300kHz 96 1F D1 10 3.3V OUTPUT POWER INPUT 2.5V TO 20V 95 VCC PVCC C C 1F + IN1 + IN2 ADP1821 2.2F 2.2F 94 25V 25V BST 2 SHDN 0.47F 93 DH M1 OUTPUT FREQ 100k L1 = 1H 1.8V, 20A SW 1.8V OUTPUT 92 SYNC 3.3k CSL C C OUT1 OUT2 PWGD + M2 M3 10F 820F 91 DL 300 COMP 6.3V 2.5V 2 2 PGND 4.7k 90 SS FB 10nF GND 2k 1.5nF 89 100nF 6.8nF 1k 88 AGND C : MURATA, GRM31MR71E225k f = 300kHz 87 SW IN1 C : SANYO, OSCON 20SP180M M1: IRLR7807Z IN2 0 2 4 6 8 10 12 14 16 M2, M3: IRFR3709Z C : SANYO, OSCON 2R5SEPC820M OUT2 L1: COILTRONICS, HC7-1R0 D1: VISHAY BAT54 LOAD CURRENT (A) Figure 1. Typical Operating Circuit Figure 2. Efficiency vs. Load Current, 5 V Input Rev. C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 20052007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 05310-001 EFFICIENCY (%) 05310-002ADP1821 TABLE OF CONTENTS Features .............................................................................................. 1 Compensation............................................................................. 11 Applications....................................................................................... 1 Power-Good Indicator............................................................... 11 General Description ......................................................................... 1 Thermal Shutdown .................................................................... 11 Revision History ............................................................................... 2 Shutdown Control...................................................................... 11 Specifications..................................................................................... 3 Application Information................................................................ 12 Absolute Maximum Ratings............................................................ 5 Selecting the Input Capacitor ................................................... 12 ESD Caution.................................................................................. 5 Output LC Filter ......................................................................... 12 Simplified Block Diagram ........................................................... 5 Selecting the MOSFETs ............................................................. 13 Pin Configuration and Function Descriptions............................. 6 Setting the Current Limit .......................................................... 14 Typical Performance Characteristics ............................................. 7 Feedback Voltage Divider ......................................................... 14 Theory of Operation ........................................................................ 9 Compensating the Voltage Mode Buck Regulator................. 14 Soft Start ........................................................................................ 9 Setting the Soft Start Period...................................................... 18 Error Amplifier............................................................................. 9 PCB Layout Guideline ................................................................... 19 Current-Limit Scheme................................................................. 9 Recommended Component Manufacturers........................... 20 MOSFET Drivers........................................................................ 10 Application Circuits ....................................................................... 21 Input Voltage Range................................................................... 10 Outline Dimensions....................................................................... 23 Setting the Output Voltage........................................................ 10 Ordering Guide .......................................................................... 23 Switching Frequency Control and Synchronization.............. 10 REVISION HISTORY Changes to Theory of Operation Section.......................................9 4/07Rev. B to Rev. C Changes to Application Information Section ............................. 12 Changes to Specifications Section.................................................. 3 Added PCB Layout Section........................................................... 19 Changes to Absolute Maximum Ratings Section......................... 5 Changes to Application Circuits Section..................................... 21 Changes to Current-Limit Scheme Section ................................ 10 Added Summary of Equations Section........................................ 23 Changes to Setting the Current Limit Section............................ 14 Added Figure 15.............................................................................. 14 1/06Rev. 0 to Rev. A Changes to Compensating the Voltage Mode Buck Changes to Specifications Table ......................................................3 Regulator Section............................................................................ 15 Changes to Theory of Operation Section.................................... 10 Changes to Type II Compensator Section................................... 17 Changes to Input Voltage Range Section .................................... 11 Changes to Type III Compensator Section ................................. 18 Added Equation 1........................................................................... 12 Changes to Application Circuits Section..................................... 21 Changes to Equation 7 and Equation 8 ....................................... 13 Changes to Figure 22...................................................................... 21 Added Equation 9........................................................................... 13 Changes to Ordering Guide .......................................................... 23 Changes to Equation 16................................................................. 14 12/06Rev. A to Rev. B Changes to Figure 15...................................................................... 14 Updated Format..................................................................Universal Changes to Equation 21................................................................. 15 Changes to Features Section............................................................ 1 Changes to Figure 16...................................................................... 15 Changes to Applications Section .................................................... 1 Changes to Equation 28................................................................. 15 Changes to General Description Section ...................................... 1 Updated Outline Dimensions....................................................... 18 Changes to Error Amplifier............................................................. 3 7/05Revision 0: Initial Version Changes to PWM Controller .......................................................... 3 Changes to Oscillator Frequency.................................................... 3 Rev. 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