LTC1735 Datasheet, PDF (1/32 Pages) Linear Technology – High Efficiency Synchronous Step-Down Switching Regulator

FEATURES
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{Synchronizable/Programmable Fixed Frequency}
s _{Wide VIN Range: 3.5V to 36V Operation}
s _{VOUT Range: 0.8V to 6V}
s _OPTI-LOOP^TM _{Compensation Minimizes COUT}
s _{±1% Output Voltage Accuracy}
s _{Internal Current Foldback}
s _{Output Overvoltage Crowbar Protection}
s _{Latched Short-Circuit Shutdown Timer}
with Defeat Option
s _{Very Low Dropout Operation: 99% Duty Cycle}
s _{Forced Continuous Control Pin}
s _{Optional Programmable Soft-Start}
s _{Remote Output Voltage Sense}
s _{Logic Controlled Micropower Shutdown: IQ < 25µA}
s _{LTC1435 Pin Compatible with}
Minor Component Changes
s _{Available in 16-Lead Narrow SSOP and SO Packages}
U
APPLICATIO S
s _{Notebook and Palmtop Computers, PDAs}
s _{Cellular Telephones and Wireless Modems}
s _{DC Power Distribution Systems}
LTC1735
High Efficiency
Synchronous Step-Down
Switching Regulator
DESCRIPTIO
The LTC^®1735 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. The precision 0.8V reference is compatible with
future microprocessor generations. OPTI-LOOP compen-
sation allows the transient response to be optimized over
a wide range of output capacitance and ESR values.
The operating frequency (synchronizable up to 500kHz) is
set by an external capacitor allowing maximum flexibility
in optimizing efficiency. A forced continuous control pin
reduces noise and RF interference and can assist second-
ary winding regulation by disabling Burst Mode operation
when the main output is lightly loaded.
Protection features include internal foldback current lim-
iting, output overvoltage crowbar and optional short-
circuit shutdown. Soft-start is provided by an external
capacitor that 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 and OPTI-LOOP are trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
C_OSC
C_OSC
TG
47pF
RUN/SS
C_SS
0.1µF
C_C
330pF
R_C
33k
BOOST
I_TH
SW
C_C2
100pF
LTC1735
V_IN
SGND
100pF
V_OSENSE
INTV_CC
BG
SENSE^–
1000pF
SENSE⁺
PGND
C_B
0.22µF
M1
FDS6680A
C_IN
22µF
50V
V_IN
5V TO 24V
C_OUT: PANASONIC EEFUEOG181R
C_IN: MARCON THCR70E1H226ZT
L1: PANASONIC ETQP6FZR0HFA
R_SENSE: IRC LRF2010-01-R005J
D_B
CMDSH-3
L1
2µH
R_SENSE
0.005Ω
+
4.7µF
M2
FDS6680A
D1
MBRS340T3
R1
20k
1% ₊
R2
20k
1%
V_OUT
1.6V
9A
C_OUT
180µF
4V
×4
SP
1735 F01
Figure 1. High Efficiency Step-Down Converter
1