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LTC1538-AUX/LTC1539
Dual High Efficiency,
Low Noise, Synchronous
Step-Down Switching Regulators
Figure 1. High Efficiency Dual 5V/3V Step-Down Converter
BOOST 2BOOST 1
TGL2
TGS2
SW2
BG2
SENSE
+
2
SENSE
–
2
V
OSENSE2
I
TH2
TGL1
M3*
M1
M2
TGS1
D1
MBR140T3
V
OUT1
5V
3.5A
V
OUT2
3.3V
3.5A
L1
10µH
SW1
BG1 LTC1539
SENSE
+
1
SENSE
–
1
C
SS1
0.1µF
C
C1
1000pF
C
OUT1
220µF
10V
R
SENSE1
0.03Ω
R
SENSE2
0.03Ω
C
OUT
220µF
10V
R
C1
10k
I
TH1
RUN/SS2PGNDSGNDV
PROG2
C
DSC
INTV
CC
D
B2
, CMDSH-3D
B1
, CMDSH-3
V
IN
V
PROG1
RUN/SS1
D2
MBR140T3
C
B1
0.1µF
C
B2
,
0.1µF
4.7µF
16V
M6*
1538 F01
M4
1000pF
1000pF
C
OSC
56pF
C
SS2
0.1µF
C
C1A
220pF
M1, M2, M4, M5: Si4412DY M3, M6: IRLML2803 *NOT REQUIRED FOR LTC1538-AUX
C
C2A
470pF
C
C2
1000pF
R
C2
10k
+
L2
10µH
V
IN
5.2V TO 28V
5V STANDBY
+
+
C
IN
22µF
35V
× 4
+
BOLD LINES INDICATE HIGH CURRENT PATHS
M5
TYPICAL APPLICATION
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■
Maintains Constant Frequency at Low Output Currents
■
Dual N-Channel MOSFET Synchronous Drive
■
Programmable Fixed Frequency (PLL Lockable)
■
Wide V
IN
Range: 3.5V to 36V Operation
■
Ultrahigh Efficiency
■
Very Low Dropout Operation: 99% Duty Cycle
■
Low Dropout, 0.5A Linear Regulator for VPP
Generation or Low Noise Audio Supply
■
Built-In Power-On Reset Timer
■
Programmable Soft Start
■
Low-Battery Detector
■
Remote Output Voltage Sense
■
Foldback Current Limiting (Optional)
■
Pin Selectable Output Voltage
■
5V Standby Regulator Active in Shutdown: I
Q
< 200µA
■
Output Voltages from 1.19V to 9V
■
Available in 28- and 36-Lead SSOP Packages
The LTC
®
1538-AUX/LTC1539 are dual, synchronous step-
down switching regulator controllers which drive external
N-channel power MOSFETs in a phase-lockable fixed
frequency architecture. The Adaptive Power
TM
output stage
selectively drives two N-channel MOSFETs at frequencies
up to 400kHz while reducing switching losses to maintain
high efficiencies at low output currents.
An auxiliary 0.5A linear regulator using an external PNP
pass device provides a low noise, low dropout voltage
source. A secondary winding feedback control pin (SFB1)
guarantees regulation regardless of load on the main
output by forcing continuous operation.
A 5V/20mA regulator, internal 1.19V reference and an
uncommitted comparator remain active when both con-
trollers are shut down. A power-on reset timer (POR) is
included which generates a signal delayed by 65536/f
CLK
(typ 300ms) after the controller’s output is within 5% of
the regulated first voltage. Internal resistive dividers pro-
vide pin selectable output voltages with remote sense
capability on one of the two outputs.
The operating current levels are user-programmable via
external current sense resistors. Wide input supply range
allows operation from 3.5V to 30V (36V maximum).
FEATURES
DESCRIPTION
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, LTC and LT are registered trademarks of Linear Technology Corporation.
Adaptive Power is a trademark of Linear Technology Corporation.
■
Notebook and Palmtop Computers, PDAs
■
Portable Instruments
■
Battery-Operated Devices
■
DC Power Distribution Systems
APPLICATIONS
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