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Analog Devices Semiconductor Electronic Components Datasheet

ADP1870 Datasheet

(ADP1870 / ADP1871) Synchronous Buck Controller

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Synchronous Buck Controller with
Constant On-Time and Valley Current Mode
ADP1870/ADP1871
FEATURES
Power input voltage range: 2.95 V to 20 V
On-board bias regulator
Minimum output voltage: 0.6 V
0.6 V reference voltage with ±1.0% accuracy
Supports all N-channel MOSFET power stages
Available in 300 kHz, 600 kHz, and 1.0 MHz options
No current-sense resistor required
Power saving mode (PSM) for light loads (ADP1871 only)
Resistor-programmable current-sense gain
Thermal overload protection
Short-circuit protection
Precision enable input
Integrated bootstrap diode for high-side drive
Starts into a precharged load
Small, 10-lead MSOP package
APPLICATIONS
Telecom and networking systems
Mid to high end servers
Set-top boxes
DSP core power supplies
GENERAL DESCRIPTION
The ADP1870/ADP1871 are versatile current-mode, synchronous
step-down controllers that provide superior transient response,
optimal stability, and current-limit protection by using a constant
on-time, pseudo-fixed frequency with a programmable current-
limit, current-control scheme. In addition, these devices offer
optimum performance at low duty cycles by utilizing valley
current-mode control architecture. This allows the ADP1870/
ADP1871 to drive all N-channel power stages to regulate output
voltages as low as 0.6 V.
The ADP1871 is the power saving mode (PSM) version of the
device and is capable of pulse skipping to maintain output
regulation while achieving improved system efficiency at light
loads (see the Power Saving Mode (PSM) Version (ADP1871)
section for more information).
Available in three frequency options (300 kHz, 600 kHz, and
1.0 MHz, plus the PSM option), the ADP1870/ADP1871 are well
suited for a wide range of applications that require a single-input
power supply range from 2.95 V to 20 V. Low voltage biasing is
supplied via a 5 V internal LDO.
TYPICAL APPLICATIONS CIRCUIT
VIN = 2.95V TO 20V
CC
VOUT RTOP
RC
CC2
RBOT
CVREG2
VIN
ADP1870/
ADP1871
COMP/EN BST
FB DRVH
GND
SW
VREG DRVL
PGND
CVREG
CIN
CBST
Q1 L
VOUT
COUT
Q2
RRES
LOAD
Figure 1.
100
95 VIN = 5V (PSM)
90
85
80
75
70 VIN = 16.5V
65
60 VIN = 13V
55 VIN = 13V (PSM)
50
45
40 VIN = 16.5V (PSM)
35
30
25
10
100
TA = 25°C
VOUT = 1.8V
fSW = 300kHz
WÜRTH INDUCTOR:
744325120, L = 1.2µH, DCR = 1.8m
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
1k 10k 100k
LOAD CURRENT (mA)
Figure 2. Efficiency vs. Load Current (VOUT = 1.8 V, 300 kHz)
In addition, an internally fixed soft start period is included to limit
input in-rush current from the input supply during startup and
to provide reverse current protection during soft start for a pre-
charged output. The low-side current-sense, current-gain scheme
and integration of a boost diode, along with the PSM/forced pulse-
width modulation (PWM) option, reduce the external part count
and improve efficiency.
The ADP1870/ADP1871 operate over the −40°C to +125°C
junction temperature range and are available in a 10-lead MSOP
package.
Rev. 0
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
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.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2010 Analog Devices, Inc. All rights reserved.


Analog Devices Semiconductor Electronic Components Datasheet

ADP1870 Datasheet

(ADP1870 / ADP1871) Synchronous Buck Controller

No Preview Available !

ADP1870 pdf
ADP1870/ADP1871
TABLE OF CONTENTS
Features .............................................................................................. 1 
Applications....................................................................................... 1 
General Description ......................................................................... 1 
Typical Applications Circuit............................................................ 1 
Revision History ............................................................................... 2 
Specifications..................................................................................... 3 
Absolute Maximum Ratings............................................................ 5 
Thermal Resistance ...................................................................... 5 
Boundary Condition.................................................................... 5 
ESD Caution.................................................................................. 5 
Pin Configuration and Function Descriptions............................. 6 
Typical Performance Characteristics ............................................. 7 
ADP1870/ADP1871 Block Diagram............................................ 18 
Theory of Operation ...................................................................... 19 
Startup.......................................................................................... 19 
Soft Start ...................................................................................... 19 
Precision Enable Circuitry ........................................................ 19 
Undervoltage Lockout ............................................................... 19 
On-Board Low Dropout Regulator.......................................... 19 
Thermal Shutdown..................................................................... 20 
Programming Resistor (RES) Detect Circuit.......................... 20 
Valley Current-Limit Setting .................................................... 20 
Hiccup Mode During Short Circuit......................................... 21 
Synchronous Rectifier................................................................ 22 
REVISION HISTORY
3/10—Revision 0: Initial Version
Power Saving Mode (PSM) Version (ADP1871) ................... 22 
Timer Operation ........................................................................ 22 
Pseudo-Fixed Frequency ........................................................... 23 
Applications Information .............................................................. 24 
Feedback Resistor Divider ........................................................ 24 
Inductor Selection ...................................................................... 24 
Output Ripple Voltage (ΔVRR) .................................................. 24 
Output Capacitor Selection....................................................... 24 
Compensation Network ............................................................ 25 
Efficiency Considerations ......................................................... 26 
Input Capacitor Selection.......................................................... 27 
Thermal Considerations............................................................ 28 
Design Example.......................................................................... 29 
External Component Recommendations.................................... 31 
Layout Considerations................................................................... 33 
IC Section (Left Side of Evaluation Board)............................. 37 
Power Section ............................................................................. 37 
Differential Sensing.................................................................... 38 
Typical Applications Circuits........................................................ 39 
15 A, 300 kHz High Current Application Circuit.................. 39 
5.5 V Input, 600 kHz Application Circuit ............................... 39 
300 kHz High Current Application Circuit ............................ 40 
Outline Dimensions ....................................................................... 41 
Ordering Guide .......................................................................... 41 
Rev. 0 | Page 2 of 44


Part Number ADP1870
Description (ADP1870 / ADP1871) Synchronous Buck Controller
Maker Analog Devices
Total Page 30 Pages
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