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use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
a
ADP1147-3.3/ADP1147-5
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
Analog Devices, Inc., 1998
Hgh Efficiency Step-Down
Swtching Regulator Controllers
FUNCT IONAL BLOCK DIAGRAM
Q
R
S
V
IN
SENSE(–)
V
TH2
SLEEP
V
OS
1.25V
OFF-TIME
CONTROL
5pF
100k
V
13k
V
V
IN
P-DRIVE GROUND
SENSE(+)
SENSE(–)
C
T
I
TH
SHUTDOWN
ADP1147
10mV to 150mV
R
S
Q
1
2
C
V
G
S
T
B
V
TH1
REFERENCE
FEATURES
Greater Than 95% Efficiency
Current Mode Switching Architecture Provides
Superior Load and Line Transient Response
Wide Input Voltage Range 3.5 V* to 16 V
User Defined Current Limit
Short Circuit Protection
Shutdown Pin
Low Dropout Voltage
Low Standby Current 160
m
A typ
Low Cost
Available in 8-Lead PDIP or 8-Lead SOIC
APPLICATIONS
Portable Computers
Modems
Cellular Telephones
Portable Equipment
GPS Systems
Handheld Instruments
GE NE RAL DE SCRIPT ION
T he ADP1147 is part of a family of High Efficiency Step-Down
Switching Regulators. T hese regulators offer superior load and
line transient response, a user defined current limit and an
automatic power savings mode. T he automatic power savings
mode is used to maintain efficiency at lower output currents.
T he ADP1147
incorporates
a constant off-time
,
current mode
switching architecture to drive an external P-channel MOSFET
at frequencies up to 250 kHz
.
Constant off-time switching gen-
erates a constant ripple current in the external inductor. T his
results in a wider input voltage operating range of 3.5 V* to
16 V, and a less complex circuit design.
*
3.5 volt operation is for the ADP1147-3.3.
1000pF
SHUTDOWN
L
*
50
m
H
D1
1
m
F
0V = NORMAL
1.5V = SHUTDOWN
R
SENSE
**
V
R
C
1k
V
C
3300pF
C
T
470pF
V
IN
(5.2V TO 12V)
C
IN
100
m
F
V
OUT
5V/2A
C
OUT
390
m
F
P-IRF7204
SHUTDOWN
I
TH
GND
P-DRIVE
SENSE(–)
ADP1147
C
T
V
IN
SENSE(+)
+
+
+
*COILTRONICS CTX 50–2MP
**KRL SL-1-C1-0R050J
Figure 1. High Efficiency Step-Down Converter
(Typical Application)
A very low dropout voltage with excellent output regulation can
be obtained by minimizing the dc resistance of the Inductor, the
R
SENSE
resistor, and the R
DS(ON)
of the P-MOSFET . T he power
savings mode conserves power by reducing switching losses at
lower output currents. When the output load current falls below
the minimum required for the continuous mode the ADP1147
will automatically switch to the power savings mode. It will remain
in this mode until the inductor requires additional current or the
sleep mode is entered. In sleep mode with no load the standby
power consumption of the device is reduced to 2.0 mW typical
at V
IN
= 10 V.
For designs requiring even greater efficiencies refer to the
ADP1148 data sheet.
LOAD CURRENT – mA
100
95
60
1
10k
10
100
1k
90
85
65
80
75
70
V
IN
= 6 VOLTS
V
IN
= 10 VOLTS
E
Figure 2. ADP1147-5 Typical Efficiency, Figure 1 Circuit