Synchronous Current-Mode with Constant On-Time, PWM Buck Controller Data Sheet ADP1872/ADP1873 FEATURES TYPICAL APPLICATIONS CIRCUIT V = 2.75V TO 20V IN Power input voltage as low as 2.75 V to 20 V Bias supply voltage range: 2.75 V to 5.5 V VIN Minimum output voltage: 0.6 V C C ADP1872/ C IN C C2 0.6 V reference voltage with 1.0% accuracy R ADP1873 C COMP/EN BST Supports all N-channel MOSFET power stages C R BST Q1 TOP L V V FB DRVH Available in 300 kHz, 600 KHz, and 1.0 MHz options OUT OUT R BOT + No current-sense resistor required C GND SW OUT Q2 C Power saving mode (PSM) for light loads (ADP1873 only) VDD2 VDD DRVL V = 2.75V DD PGND Resistor-programmable current-sense gain R LOAD TO 5.5V RES 5A Thermal overload protection C VDD Short-circuit protection Figure 1. Precision enable input Integrated bootstrap diode for high-side drive 100 V = 5.5V, V = 5.5V (PSM) V = 5.5V, V = 5.5V DD IN DD IN 140 A shutdown supply current 95 Starts into a precharged load 90 Small, 10-lead MSOP package 85 V = 5.5V, V = 13.0V (PSM) 80 DD IN APPLICATIONS 75 Telecom and networking systems V = 5.5V, V = 16.5V (PSM) DD IN 70 Mid to high end servers 65 Set-top boxes T = 25C A V = 1.8V OUT 60 DSP core power supplies f = 300kHz SW 55 WURTH INDUCTOR: 744325120, L = 1.2H, DCR = 1.8m 50 INFINEON FETs: BSC042N03MS G (UPPER/LOWER) 45 100 1k 10k 100k LOAD CURRENT (mA) Figure 2. ADP1872 Efficiency vs. Load Current (V = 1.8 V, 300 kHz) OUT GENERAL DESCRIPTION The ADP1872/ADP1873 are versatile current-mode, synchronous Available in three frequency options (300 kHz, 600 kHz, and step-down controllers that provide superior transient response, 1.0 MHz, plus the PSM option), the ADP1872/ADP1873 are optimal stability, and current limit protection by using a constant well suited for a wide range of applications. These ICs not only on-time, pseudo-fixed frequency with a programmable current- operate from a 2.75 V to 5.5 V bias supply, but can also accept a sense gain, current-control scheme. In addition, these devices offer power input as high as 20 V. optimum performance at low duty cycles by using valley current- In addition, an internally fixed, soft start period is included to limit mode control architecture. This allows the ADP1872/ADP1873 input in-rush current from the input supply during startup and to drive all N-channel power stages to regulate output voltages to provide reverse current protection during soft start for a pre- as low as 0.6 V. charged output. The low-side current-sense, current-gain scheme The ADP1873 is the power saving mode (PSM) version of the and integration of a boost diode, along with the PSM/forced pulse- device and is capable of pulse skipping to maintain output width modulation (PWM) option, reduce the external part count regulation while achieving improved system efficiency at light and improve efficiency. loads (see the Power Saving Mode (PSM) Version (ADP1873) The ADP1872/ADP1873 operate over the 40C to +125C section for more information). junction temperature range and are available in a 10-lead MSOP. Rev. B 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. Trademarks and registered trademarks are the property of their respective owners. Fax: 781.461.3113 20092012 Analog Devices, Inc. All rights reserved. EFFICIENCY (%) 08297-001 08297-002ADP1872/ADP1873 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Timer Operation ........................................................................ 21 Applications ....................................................................................... 1 Pseudo-Fixed Frequency ........................................................... 22 Typical Applications Circuit ............................................................ 1 Applications Information .............................................................. 23 General Description ......................................................................... 1 Feedback Resistor Divider ........................................................ 23 Revision History ............................................................................... 2 Inductor Selection ...................................................................... 23 Specif icat ions ..................................................................................... 3 Output Ripple Voltage (V ) .................................................. 23 RR Absolute Maximum Ratings ............................................................ 5 Output Capacitor Selection ....................................................... 23 Thermal Resistance ...................................................................... 5 Compensation Network ............................................................ 24 Boundary Condition .................................................................... 5 Efficiency Consideration ........................................................... 25 ESD Caution .................................................................................. 5 Input Capacitor Selection .......................................................... 26 Pin Configuration and Function Descriptions ............................. 6 Thermal Considerations ............................................................ 27 Typical Performance Characteristics ............................................. 7 Design Example .......................................................................... 27 ADP1872/ADP1873 Block Digram .............................................. 17 External Component Recommendations .................................... 30 Theory of Operation ...................................................................... 18 Layout Considerations ................................................................... 32 Startup .......................................................................................... 18 IC Section (Left Side of Evaluation Board) ............................. 37 Soft Start ...................................................................................... 18 Power Section ............................................................................. 37 Precision Enable Circuitry ........................................................ 18 Differential Sensing .................................................................... 37 Undervoltage Lockout ............................................................... 18 Typical Application Circuits ......................................................... 38 Thermal Shutdown ..................................................................... 18 Dual-Input, 300 kHz High Current Application Circuit ...... 38 Programming Resistor (RES) Detect Circuit .......................... 19 Single-Input, 600 kHz Application Circuit ............................. 38 Valley Current-Limit Setting .................................................... 19 Dual-Input, 300 kHz High Current Application Circuit ...... 39 Hiccup Mode During Short Circuit ......................................... 20 Outline Dimensions ....................................................................... 40 Synchronous Rectifier ................................................................ 21 Ordering Guide .......................................................................... 40 Power Saving Mode (PSM) Version (ADP1873) .................... 21 REVISION HISTORY 7/12Rev. A to Rev. B Changes to Table 9 .......................................................................... 31 Changes to Figure 82 ...................................................................... 32 Changed RON = 15 m/100 k Valley Current Level Value from Changes to Figure 83 ...................................................................... 33 7.5 to 3.87 Table 6 .......................................................................... 20 Changes to Figure 84 ...................................................................... 34 Changes to Ordering Guide .......................................................... 40 Changes to Figure 85 ...................................................................... 35 3/10Rev. 0 to Rev. A Changes to Figure 86 ...................................................................... 36 Changes to Figure 1 .......................................................................... 1 Changes to Differential Sensing Section and Figure 88 ............ 37 Changes to Table 1 ............................................................................ 3 Changes to Figure 89 and Figure 90............................................. 38 Changes to Table 2 ............................................................................ 5 Changes to Figure 91 ...................................................................... 39 Changes to Figure 59 Caption and Figure 60 Caption .............. 16 Updated Outline Dimensions ....................................................... 40 Changes to Figure 64 ...................................................................... 17 10/09Revision 0: Initial Version Changes to Timer Operation Section .......................................... 22 Changes to Table 7 .......................................................................... 23 Changes to Inductor Section ......................................................... 28 Rev. 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