High Efficiency Synchronous
Step-Down Switching Regulators
a
ADP1148, ADP1148-3.3, ADP1148-5
FUNCTIO NAL BLO CK D IAGRAM
ADJUSTABLE
FEATURES
Operation From 3.5 V to 18 V Input Voltage
Ultrahigh Efficiency > 95%
Low Shutdow n Current
VERSION
SIGNAL
PWR
GND
V
V
P-DRIVE N-DRIVE
GND SENSE(+)
SENSE(–)
7
IN
FB
Current Mode Operation for Excellent Line and Load
Transient Response
3
1
12
11
8
14
9
ADP1148
High Efficiency Maintained Over Wide Current Range
Logic Controlled Micropow er Shutdow n
Short Circuit Protection
NON-OVERLAP
DRIVE
V
B
2
R
Very Low Dropout Operation
SLEEP
Q
S
1
Synchronous FET Sw itching for High Efficiency
Adaptive Nonoverlap Gate Drives
Q
R
S
C
S
V
TH1
APPLICATIONS
13k⍀
10mV to
150mV
V
TH2
T
G
Notebook and Palm top Com puters
Portable Instrum ents
Battery Operated Digital Devices
Industrial Pow er Distribution
Avionics System s
100k⍀
1.25V
V
IN
OFF-TIME
CONTROL
REFERENCE
SENSE(–)
V
FB
10
5
4
6
I
SHUTDOWN
INT V
CC
C
TH
T
Telecom Pow er Supplies
GPS System s
Cellular Telephones
T he constant off-time architecture maintains constant ripple
current in the inductor, easing the design of wide input range
converters. Current-mode operation provides excellent line and
load transient response. T he operating current level is user
programmable via an external current sense resistor.
GENERAL D ESCRIP TIO N
T he ADP1148 is part of a family of synchronous step-down
switching regulator controllers featuring automatic sleep mode
to maintain high efficiencies at low output currents. T hese
devices drive external complementary power MOSFET s at
switching frequencies up to 250 kHz using a constant off-time
current-mode architecture.
T he ADP1148 incorporates automatic Power Saving Sleep
Mode operation when load currents drop below the level re-
quired for continuous operation. In sleep mode, standby power
is reduced to only about 2 mW at VIN = 10 V. In shutdown,
both MOSFET s are turned off.
TYP ICAL AP P LICATIO NS
V
(5.2V TO 18V)
IN
100
95
90
85
80
+
+
C
IN
1F
V
V
= 6V
100F
IN
V
10nF
IN
INT V
CC
P-CH
IRF7204
P-DRIVE
= 10V
IN
ADP1148
R
**
L*
SENSE
0V = NORMAL
62H
>1.5V = SHUTDOWN
0.05⍀
SHUTDOWN
V
OUT
5V/2A
I
SENSE(+)
TH
1000pF
R
C
C
SENSE(–)
N-DRIVE
T
+
C
OUT
1k⍀
75
70
N-CH
IRF7403
390F
C
T
470pF
FIGURE 1 CIRCUIT
0.02
C
C
C1
S-GND P-GND
3300pF
10BQ040
2
0.2
LOAD CURRENT – A
*COILTRONICS CTX-68-4
**KRL SL-1-C1-0R050L
Figure 1. High Efficiency Step-Down Converter
REV. A
Figure 2. ADP1148-5 Typical Efficiency
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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.
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© Analog Devices, Inc., 1997