High Efficiency Step-Down
Switching Regulator Controllers
a
ADP1147-3.3/ADP1147-5
FEATURES
FUNCTIO NAL BLO CK D IAGRAM
Greater Than 95% Efficiency
Current Mode Sw itching Architecture Provides
Superior Load and Line Transient Response
Wide Input Voltage Range 3.5 V* to 16 V
User Defined Current Lim it
Short Circuit Protection
Shutdow n Pin
Low Dropout Voltage
Low Standby Current 160 A typ
Low Cost
Available in 8-Lead PDIP or 8-Lead SOIC
V
P-DRIVE GROUND
SENSE(+)
SENSE(–)
IN
V
ADP1147
2
R
B
S
Q
1
SLEEP
Q
R
S
10mV to 150mV
5pF
C
V
OS
V
V
TH1
TH2
S
13k⍀
G
T
100k⍀
1.25V
APPLICATIONS
Portable Com puters
Modem s
V
OFF-TIME
CONTROL
REFERENCE
IN
SENSE(–)
Cellular Telephones
Portable Equipm ent
GPS System s
C
I
SHUTDOWN
T
TH
A very low dropout voltage with excellent output regulation can
be obtained by minimizing the dc resistance of the Inductor, the
RSENSE resistor, and the RDS(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 VIN = 10 V.
Handheld Instrum ents
GENERAL D ESCRIP TIO N
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.
For designs requiring even greater efficiencies refer to the
ADP1148 data sheet.
*3.5 volt operation is for the ADP1147-3.3.
100
V
= 6 VOLTS
IN
L
*
R
SENSE**
0.05⍀
95
90
85
80
75
70
65
60
P-CHANNEL
IRF7204
50H
V
(5.2V TO 12V)
+
IN
V
OUT
+
5V/2A
C
D1
30BQ040
IN
1F
V
= 10 VOLTS
+
IN
C
100F
OUT
390F
V
IN
0V = NORMAL
1.5V = SHUTDOWN
P-DRIVE
ADP1147
SHUTDOWN
C
C
R
C
3300pF
1k⍀
I
TH
SENSE(+)
SENSE(–)
1000pF
C
T
C
T
GND
470pF
*COILTRONICS CTX 50–2MP
**KRL SL-1-C1-0R050J
1
10
100
LOAD CURRENT – mA
1k
10k
SHUTDOWN
Figure 1. High Efficiency Step-Down Converter
(Typical Application)
Figure 2. ADP1147-5 Typical Efficiency, Figure 1 Circuit
REV. 0
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 781/ 329-4700
Fax: 781/ 326-8703
World Wide Web Site: http:/ / w w w .analog.com
© Analog Devices, Inc., 1998
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