LTC1438/LTC1439
Dual High Efficiency,
Low Noise, Synchronous
Step-Down Switching Regulators
FEATURES
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DESCRIPTION
The LTC
®
1438/LTC1439 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.
An additional comparator is available for use as a low
battery detector. A power-on reset timer (POR) is included
which generates a signal delayed by 65536/f
CLK
(typ
300ms) after the output is within 5% of the regulated
output voltage. Internal resistive dividers provide 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).
, LTC and LT are registered trademarks of Linear Technology Corporation.
Adaptive Power is a trademark of Linear Technology Corporation.
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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
Logic-Controlled Micropower Shutdown: I
Q
< 30µA
Output Voltages from 1.19V to 9V
Available in 28- and 36-Lead SSOP Packages
APPLICATIONS
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Notebook and Palmtop Computers, PDAs
Portable Instruments
Battery-Operated Devices
DC Power Distribution Systems
TYPICAL APPLICATION
D
B1
, CMDSH-3
BOOST 1
M1
L1
10µH
D1
MBR140T3
M3*
C
B1
0.1µF
M2
TGL1
TGS1
SW1
BG1
SENSE 1
R
SENSE1
0.03Ω
V
OUT1
5V
3.5A
1000pF
C
C1
1000pF
C
C1A
220pF
SENSE
–
1
I
TH1
RUN/SS1
R
C1
10k
C
SS1
0.1µF
C
DSC
V
PROG2
C
OSC
56pF
SGND
V
OSENSE2
I
TH2
PGND RUN/SS2
C
SS2
0.1µF
C
C2
1000pF
R
C2
10k
C
C2A
470pF
+
D
B2
, CMDSH-3
V
PROG1
V
IN
INTV
CC
BOOST 2
TGL2
TGS2
SW2
BG2
LTC1439
SENSE
+
2
SENSE
–
2
+
4.7µF
16V
C
B2
, 0.1µF
M5
1000pF
+
C
OUT1
220µF
10V
M1, M2, M4, M5: Si4412DY
M3, M6: IRLML2803
*NOT REQUIRED FOR LTC1438
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 1. High Efficiency Dual 5V/3V Step-Down Converter
U
U
U
+
C
IN
22µF
35V
×
4
V
IN
5.2V TO 28V
M4
M6*
L2
10µH
D2
MBR140T3
R
SENSE2
0.03Ω
V
OUT2
3.3V
3.5A
+
1438 F01
C
OUT
220µF
10V
1
LINER [ LINEAR TECHNOLOGY ]
