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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
High Efficiency Step-Down
Switching Regulator Controllers
FUNCTIONAL BLOCK DIAGRAM
Q R
S
V
IN
SENSE(–)
V
TH2
SLEEP
V
OS
1.25V
OFF-TIME
CONTROL
5pF
100kV
13kV
V
IN P-DRIVE GROUND SENSE(+) SENSE(–)
C
T
I
TH
SHUTDOWN
ADP1147
10mV to 150mV
R
SQ
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 mA typ
Low Cost
Available in 8-Lead PDIP or 8-Lead SOIC
APPLICATIONS
Portable Computers
Modems
Cellular Telephones
Portable Equipment
GPS Systems
Handheld Instruments
GENERAL DESCRIPTION
The ADP1147 is part of a family of High Efficiency Step-Down
Switching Regulators. These regulators offer superior load and
line transient response, a user defined current limit and an
automatic power savings mode. The automatic power savings
mode is used to maintain efficiency at lower output currents.
The 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. This
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*
50mH
D1
30BQ040
1mF
0V = NORMAL
1.5V = SHUTDOWN
R
SENSE
**
0.05V
R
C
1kV
C
C
3300pF
C
T
470pF
V
IN
(5.2V TO 12V)
C
IN
100mF
V
OUT
5V/2A
C
OUT
390mF
P-CHANNEL
IRF7204
SHUTDOWN
GND
P-DRIVE
SENSE(–)
ADP1147
I
TH
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. The 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 10k10 100 1k
90
85
65
80
75
70
V
IN
= 6 VOLTS
V
IN
= 10 VOLTS
EFFICIENCY – %
Figure 2. ADP1147-5 Typical Efficiency, Figure 1 Circuit