Synchronous Buck Controller with
Constant On-Time and Valley Current Mode
ADP1870/ADP1871
FEATURES
TYPICAL APPLICATIONS CIRCUIT
V
= 2.95V TO 20V
IN
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
VIN
C
C
ADP1870/
ADP1871
COMP/EN BST
C
IN
C
C2
R
C
R
TOP
V
OUT
C
Q1
BST
L
V
FB
DRVH
SW
OUT
R
BOT
C
GND
OUT
Q2
C
VREG2
VREG
DRVL
PGND
R
RES
LOAD
C
VREG
Short-circuit protection
Figure 1.
Precision enable input
Integrated bootstrap diode for high-side drive
Starts into a precharged load
Small, 10-lead MSOP package
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
V
= 5V (PSM)
IN
APPLICATIONS
Telecom and networking systems
Mid to high end servers
Set-top boxes
V
= 16.5V
IN
V
= 13V
IN
DSP core power supplies
V
= 13V (PSM)
IN
T
V
= 25°C
A
= 1.8V
OUT
= 300kHz
f
SW
V
= 16.5V (PSM)
IN
GENERAL DESCRIPTION
WÜRTH INDUCTOR:
744325120, L = 1.2µH, DCR = 1.8mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
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.
10
100
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 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).
The ADP1870/ADP1871 operate over the −40°C to +125°C
junction temperature range and are available in a 10-lead MSOP
package.
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.
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.
Trademarks and registeredtrademarks arethe property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
www.analog.com
©2010 Analog Devices, Inc. All rights reserved.
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