LTC1435A_15 Datasheet, PDF (1/20 Pages) Linear Technology – High Efficiency Low Noise Synchronous Step-Down Switching Regulator

FEATURES
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{Programmable Fixed Frequency}
s _{Wide VIN Range: 3.5V to 36V Operation}
s _{Low Minimum On-Time (≤300ns) for High}
Frequency, Low Duty Cycle Applications
s _{Very Low Dropout Operation: 99% Duty Cycle}
s _{Low Standby Current}
s _{Secondary Feedback Control}
s _{Programmable Soft Start}
s _{Remote Output Voltage Sense}
s _{Logic Controlled Micropower Shutdown: IQ < 25µA}
s _{Foldback Current Limiting (Optional)}
s _{Current Mode Operation for Excellent Line and Load}
Transient Response
s _{Output Voltages from 1.19V to 9V}
s _{Available in 16-Lead Narrow SO and SSOP Packages}
U
APPLICATIONS
s _{Notebook and Palmtop Computers, PDAs}
s _{Cellular Telephones and Wireless Modems}
s _{Portable Instruments}
s _{Battery-Operated Devices}
s _{DC Power Distribution Systems}
LTC1435A
High Efficiency Low Noise
Synchronous Step-Down
Switching Regulator
DESCRIPTION
The LTC^®1435A is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using a fixed frequency architecture. A wide
duty cycle range of 5% to 99% allows high V_IN to low V_OUT
DC/DC conversion, as well as low dropout operation that
extends operating time in battery-operated systems. Burst
Mode^TM operation provides high efficiency at low load
currents.
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 that can be
used to properly sequence supplies. The operating cur-
rent 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.
TYPICAL APPLICATION
C_OSC
43pF
C_SS
0.1µF
C_OSC
V_IN
RUN/SS
TG
C_C
I_TH
SW
330pF
LTC1435A
R_C
INTV_CC
10k
100pF
SGND
V_OSENSE
BOOST
BG
PGND
SENSE^– SENSE⁺
1000pF
V_IN
4.5V TO 22V
+
M1
Si4412DY
C_IN
22µF
35V
×2
D_B
CMDSH-3
C_B
0.1µF
L1
4.7µH
R_SENSE
0.033Ω
+
4.7µF
M2
Si4412DY
D1
MBRS140T3
R1
35.7k
R2
102k
V_OUT
1.6V/3A
C_OUT
100µF
6.3V
×2
1435A F01
Figure 1. High Efficiency Step-Down Converter
1