LTC1435
High Efficiency Low Noise
Synchronous Step-Down
Switching Regulator
U
FEATURES
DESCRIPTION
The LTC®1435 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using a fixed frequency architecture. Burst
ModeTM operation provides high efficiency at low load
currents.Amaximumdutycyclelimitof99%provideslow
dropout operation which extends operating time in bat-
tery-operated systems.
■
Dual N-Channel MOSFET Synchronous Drive
■
Programmable Fixed Frequency
■
Wide VIN Range: 3.5V to 36V Operation
■
Ultrahigh Efficiency
■
Very Low Dropout Operation: 99% Duty Cycle
■
Low Standby Current
■
Secondary Feedback Control
■
Programmable Soft Start
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.
■
Remote Output Voltage Sense
■
Logic Controlled Micropower Shutdown: IQ < 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-LUead Narrow SO and SSOP Packages
Soft start is provided by an external capacitor which can
be used to properly sequence supplies. The operating
currentlevelisuser-programmableviaanexternalcurrent
sense resistor. Wide input supply range allows operation
from 3.5V to 30V (36V maximum).
APPLICATIONS
■
Notebook and Palmtop Computers, PDAs
Cellular Telephones and Wireless Modems
Portable Instruments
Battery-Operated Devices
■
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
■
■
DC Power Distribution Systems
U
TYPICAL APPLICATION
V
IN
4.5V TO 28V
C
V
IN
OSC
C
IN
+
C
OSC
22µF
35V
× 2
M1
Si4412DY
RUN/SS
TG
68pF
C
R
SS
0.1µF
SENSE
0.033Ω
V
OUT
I
SW
TH
2.9V/3.5A
L1
C
D
C
B
LTC1435
INTV
10µH
330pF
CMDSH-3
R1
C
C
R
OUT
B
C
32.4k
CC
+
100µF
10V
0.1µF
10k
SGND
BOOST
R2
22.1k
× 2
D1
MBRS140T3
+
100pF
4.7µF
M2
Si4412DY
V
BG
OSENSE
PGND
SENSE
–
+
SENSE
1000pF
1435 F01
Figure 1. High Efficiency Step-Down Converter
1
Linear [ Linear ]
