Datasheet ADP1821 (Analog Devices)

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 μA shutdown supply current Small, 16-lead QSOP
The ADP1821 operates at a pin-selectable, fixed switching 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 –40°C to +125°C junction temperature range and is available in a 16-lead QSOP.
BIAS INPUT 97 5V TA = 25°C FREQUENCY = 300kHz 1µF 96 10Ω D1 POWER INPUT 3.3V OUTPUT 2.5V TO 20V 95 VCC PVCC 1µF ADP1821 + CIN1 + CIN2 2.2µF 2.2µF 94 25V 25V ) BST ×2 SHDN 0.47µF (% 93 DH M1 Y FREQ OUTPUT 100kΩ C SW L1 = 1µH 1.8V, 20A 1.8V OUTPUT SYNC 92 3.3kΩ IEN CSL C C PWGD OUT1 OUT2 M2 M3 10µF + 820µF IC DL F 91 COMP 300Ω 6.3V 2.5V EF 4.7kΩ PGND ×2 ×2 SS 90 GND FB 10nF 2kΩ 1.5nF 89 100nF 6.8nF 1kΩ AGND 88 fSW = 300kHz CIN1: MURATA, GRM31MR71E225k 87 C
2
IN2: SANYO, OSCON 20SP180M M1: IRLR7807Z
01
0 2 4 6 8 10 12 14 16
00
C
0
OUT2: SANYO, OSCON 2R5SEPC820M M2, M3: IRFR3709Z
0-
L1: COILTRONICS, HC7-1R0 D1: VISHAY BAT54
5310-
LOAD CURRENT (A)
31 0 05 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 license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Tel: 781.329.4700 www.analog.com Trademarks and registered trademarks are the property of their respective owners. Fax: 781.461.3113 ©2005–2007 Analog Devices, Inc. All rights reserved.
Document Outline FEATURES APPLICATIONS GENERAL DESCRIPTION TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ESD CAUTION SIMPLIFIED BLOCK DIAGRAM PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS THEORY OF OPERATION SOFT START ERROR AMPLIFIER CURRENT-LIMIT SCHEME MOSFET DRIVERS INPUT VOLTAGE RANGE SETTING THE OUTPUT VOLTAGE SWITCHING FREQUENCY CONTROL AND SYNCHRONIZATION COMPENSATION POWER-GOOD INDICATOR THERMAL SHUTDOWN SHUTDOWN CONTROL APPLICATION INFORMATION SELECTING THE INPUT CAPACITOR OUTPUT LC FILTER SELECTING THE MOSFETS SETTING THE CURRENT LIMIT FEEDBACK VOLTAGE DIVIDER COMPENSATING THE VOLTAGE MODE BUCK REGULATOR Type II Compensator Type III Compensator SETTING THE SOFT START PERIOD PCB LAYOUT GUIDELINE RECOMMENDED COMPONENT MANUFACTURERS APPLICATION CIRCUITS OUTLINE DIMENSIONS ORDERING GUIDE