1
LTC1435
High Efficiency Low Noise
Synchronous Step-Down
Switching Regulator
Figure 1. High Efficiency Step-Down Converter
FEATURES
DESCRIPTION
U
■
Dual N-Channel MOSFET Synchronous Drive
■
Programmable Fixed Frequency
■
Wide V
IN
Range: 3.5V to 36V Operation
■
Ultrahigh Efficiency
■
Very Low Dropout Operation: 99% Duty Cycle
■
Low Standby Current
■
Secondary Feedback Control
■
Programmable Soft Start
■
Remote Output Voltage Sense
■
Logic Controlled Micropower Shutdown: I
Q
< 25µA
■
Foldback Current Limiting (Optional)
■
Current Mode Operation for Excellent Line and Load
Transient Response
■
Output Voltages from 1.19V to 9V
■
Available in 16-Lead Narrow SO and SSOP Packages
The LTC
®
1435 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using a fixed frequency architecture. Burst
Mode
TM
operation provides high efficiency at low load
currents. A maximum duty cycle limit of 99% provides low
dropout operation which extends operating time in bat-
tery-operated systems.
The operating frequency is set by an external capacitor
allowing maximum flexibility in optimizing efficiency. A
secondary winding feedback control pin, SFB, guarantees
regulation regardless of load on the main output by
forcing continuous operation. Burst Mode operation is
inhibited when the SFB pin is pulled low which reduces
noise and RF interference.
Soft start is provided by an external capacitor which can
be used to properly sequence supplies. 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.
Burst Mode is a trademark of Linear Technology Corporation.
■
Notebook and Palmtop Computers, PDAs
■
Cellular Telephones and Wireless Modems
■
Portable Instruments
■
Battery-Operated Devices
■
DC Power Distribution Systems
APPLICATIONS
U
TYPICAL APPLICATION
U
I
TH
TG
C
OSC
68pF
C
C
330pF
100pF
R
C
10k
C
SS
0.1µF
SENSE
–
SENSE
+
LTC1435
1000pF
+
4.7µF
D
B
CMDSH-3
C
B
0.1µF
M2
Si4412DY
D1
MBRS140T3
L1
10µH
M1
Si4412DY
R
SENSE
0.033Ω
+
C
IN
22µF
35V
× 2
V
IN
4.5V TO 28V
+
C
OUT
100µF
10V
× 2
R1
32.4k
R2
22.1k
V
OUT
2.9V/3.5A
PGND
BG
C
OSC
V
IN
V
OSENSE
BOOST
1435 F01
SGND
RUN/SS
SW
INTV
CC