LTC1436A
LTC1436A-PLL/LTC1437A
High Efficiency Low Noise
Synchronous Step-Down
Switching Regulators
DESCRIPTION
The LTC
廬
1436A/LTC1437A are synchronous step-down
switching regulator controllers that 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 (SFB)
guarantees regulation regardless of the 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
(300ms
typically) after the output is within 5% of the regulated
output voltage. Internal resistive dividers provide pin
selectable output voltages with remote sense capability.
The operating current level is user-programmable via an
external current sense resistor. 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.
FEATURES
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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
Low Minimum On-Time (
鈮?/div>
300ns) for High
Frequency, Low Duty Cycle Applications
Very Low Dropout Operation: 99% Duty Cycle
Low Dropout, 0.5A Linear Regulator for CPU I/O
or Low Noise Audio Supplies
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
< 25碌A(chǔ)
Output Voltages from 1.19V to 9V
Available in 24-Lead Narrow SSOP and 28-Lead
SSOP Packages
APPLICATIONS
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Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
Portable Instruments
Battery-Operated Devices
DC Power Distribution Systems
TYPICAL APPLICATION
C
OSC
43pF
C
SS
0.1碌F
R
C
10k
C
OSC
RUN/SS
V
IN
TGL
TGS
I
TH
C
C
510pF
SGND
100pF
V
PROG
V
OSENSE
SENSE
鈥?/div>
V
IN
4.5V TO 22V
M1
Si4412DY
M3
IRLML2803
D
B
CMDSH-3
SW
LTC1436A
INTV
CC
BOOST
BG
PGND
SENSE
+
1000pF
C
B
0.1碌F
L1
4.7碌H
+
4.7碌F
M2
Si4412DY
D1
MBRS140T3
Figure 1. High Efficiency Step-Down Converter
U
U
U
+
C
IN
22碌F
35V
脳
2
R
SENSE
0.02鈩?/div>
V
OUT
1.6V
5A
R1
35.7k
R2
102k
+
C
OUT
100碌F
6.3V
脳
2
1436 F01
1
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