1
LTC1433/LTC1434
450mA, Low Noise
Current Mode Step-Down
DC/DC Converters
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Cellular Telephones
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Portable Instruments
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Wireless Modems
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RF Communications
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Distributed Power Systems
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Scanners
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Battery-Powered Equipment
DESCRIPTION
U
■
High Efficiency: Up to 93%
■
Constant Frequency Adaptive Power
TM
Operation
■
Input Voltage Range: 3V to 13.5V
■
Internal 0.6Ω Power Switch (V
IN
= 10V)
■
Low Dropout Operation: 100% Duty Cycle
■
Low-Battery Detector
■
Internal Power-On Reset Timer
■
Current Mode Operation for Excellent Line and Load
Transient Response
■
Low Quiescent Current: 470µA
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Shutdown Mode Draws Only 15µA Supply Current
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±1% Reference Accuracy
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Available in 16- and 20-Lead Narrow SSOP
FEATURES
The LTC
®
1433/LTC1434 are monolithic pulse width modu-
lated step-down DC/DC converters. By utilizing current
mode switching techniques, they provide excellent AC and
DC load and line regulation. Both devices operate at a fixed
frequency with the LTC1434 phase-lockable to an external
clock signal.
Both devices incorporate two internal P-channel power
MOSFETs with a parallel combined resistance of 0.6Ω (at
a supply of 10V). The Adaptive Power output stage selec-
tively drives one or both of the switches at frequencies up
to 700kHz to reduce switching losses and maintain high
efficiencies at low output currents.
The LTC1433/LTC1434 are capable of supplying up to
450mA of output current and boasts a ±2.4% output
voltage accuracy. An internal low-battery detector has the
same level of accuracy as the output voltage. A power-on
reset timer (POR) is included which generates a signal
delayed by 65536/f
CLK
(300ms typ) after the output is
within 5% of the regulated output voltage.
Ideal for current sensitive applications, the devices draw
only 470µA of quiescent current. In shutdown the devices
draw a mere 15µA. To further maximize the life of the
battery source, the internal P-channel MOSFET switch is
turned on continuously in dropout.
APPLICATIONS
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
Adaptive Power is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
U
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
SSW
NC
BSW
NC
SGND
RUN/SS
LBO
LBI
PWRV
IN
SV
IN
C
OSC
POR
I
TH
V
OSENSE
V
PROG
LTC1433
PGND
68µF**
20V
0.1µF
0.1µF
100µF*
10V
D1:MOTOROLA MBRS130LT3
L1: COILCRAFT D03316-104
V
OUT
3.3V
D1
L1
100µH
POWER-ON
RESET
V
IN
3.5V TO 12V
680pF
5.1k
10k
6800pF
47pF
1433/34 F01
* AVX TPSD107M010R0100
** AVX TPSE686M020R0150
+
+
Figure 1. High Efficiency Step-Down Converter
LOAD CURRENT (A)
0.001
60
EFFICIENCY (%)
70
80
0.01 0.1 1
1433/34 TA01
50
40
100
90
V
IN
= 5V
V
IN
= 12V
V
IN
= 9V
LTC1433 Efficiency for
V
OUT
= 3.3V