LTC1775 Datasheet, PDF (1/24 Pages) Linear Technology – High Power No RSENSE TM Current Mode Synchronous Step-Down Switching Regulator

FEATURES
s _{Highest Efficiency Current Mode Controller}
s _{No Sense Resistor Required}
s _{300mV Maximum Current Sense Voltage}
s _{Stable High Current Operation}
s _{Dual N-Channel MOSFET Synchronous Drive}
s _{Wide VIN Range: 4V to 36V}
s _{Wide VOUT Range: 1.19V to VIN}
s _{±1% 1.19V Reference}
s _{Programmable Fixed Frequency with Injection Lock}
s _{Very Low Drop Out Operation: 99% Duty Cycle}
s _{Forced Continuous Mode Control Pin}
s _{Optional Programmable Soft Start}
s _{Pin Selectable Output Voltage}
s _{Foldback Current Limit}
s _{Output Overvoltage Protection}
s _{Logic Controlled Micropower Shutdown: IQ < 30µA}
s _{Available in 16-Lead Narrow SSOP and SO Packages}
U
APPLICATIO S
s _{Notebook Computers}
s _{Automotive Electronics}
s _{Battery Chargers}
s _{Distributed Power Systems}
LTC1775
High Power
No R_SENSE^TM Current Mode
Synchronous Step-Down
Switching Regulator
DESCRIPTIO
The LTC^®1775 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using few external components. Current mode
control with MOSFET V_DS sensing eliminates the need for
a sense resistor and improves efficiency. Largely similar
to the LTC1625, the LTC1775 has twice the maximum
sense voltage for high current applications. The frequency
of a nominal 150kHz internal oscillator can be synchro-
nized to an external clock over a 1.5:1 frequency range.
Burst Mode^TM operation at low load currents reduces
switching losses and low dropout operation extends oper-
ating time in battery-powered systems. A forced continu-
ous mode control pin can assist secondary winding
regulation by disabling Burst Mode operation when the
main output is lightly loaded.
Fault protection is provided by foldback current limiting
and an output overvoltage comparator. An external ca-
pacitor attached to the RUN/SS pin provides soft start
capability for supply sequencing. A wide supply range
allows operation from 4V (4.3V for LTC1775I) to 36V at the
input and 1.19V to V_IN at the output.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R_SENSE and Burst Mode are trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
C_C
2.2nF
C_SS 0.1µF
LTC1775
SYNC
V_IN
TK
RUN/SS TG
V_PROG
SW
BOOST
R_C
10k
I_TH
INTV_CC
SGND
BG ₊
V_OSENSE PGND
C_B 0.33µF
D_B
CMDSH-3
C_VCC
4.7µF
+
M1
SUD50N03-10 _L1
6µH
D1
MBRS340
M2
SUD50N03-10
C_IN
22µF
V_IN
5V TO
28V
30V
×4
V_OUT
3.3V
+ C_OUT 10A
680µF
6.3V
1775 F01
Figure 1. High Efficiency Step-Down Converter
Efficiency vs Load Current
100
V_IN = 10V
f = 150kHz
95 FCB = INTV_CC
V_OUT = 5V
90
V_OUT = 3.3V
85
80
75
70
0.01
0.1
1
LOAD CURRENT (A)
10
1775 F01b
1