LTC1775
High Power
No R
SENSE
TM
Current Mode
Synchronous Step-Down
Switching Regulator
FEATURES
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DESCRIPTIO
Highest Efficiency Current Mode Controller
No Sense Resistor Required
300mV Maximum Current Sense Voltage
Stable High Current Operation
Dual N-Channel MOSFET Synchronous Drive
Wide V
IN
Range: 4V to 36V
Wide V
OUT
Range: 1.19V to V
IN
鹵1%
1.19V Reference
Programmable Fixed Frequency with Injection Lock
Very Low Drop Out Operation: 99% Duty Cycle
Forced Continuous Mode Control Pin
Optional Programmable Soft Start
Pin Selectable Output Voltage
Foldback Current Limit
Output Overvoltage Protection
Logic Controlled Micropower Shutdown: I
Q
< 30碌A(chǔ)
Available in 16-Lead Narrow SSOP and SO Packages
The LTC
廬
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.
APPLICATIO S
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Notebook Computers
Automotive Electronics
Battery Chargers
Distributed Power Systems
TYPICAL APPLICATION
LTC1775
SYNC
C
SS
0.1碌F
RUN/SS
V
PROG
R
C
10k
C
C
2.2nF
I
TH
SGND
V
IN
TK
TG
SW
BOOST
INTV
CC
BG
C
B
0.33碌F
D
B
CMDSH-3
D1
MBRS340
M2
SUD50N03-10
M1
SUD50N03-10
L1
6碌H
+
EFFICIENCY (%)
C
IN
22碌F
30V
脳
4
V
IN
5V TO
28V
+
V
OUT
3.3V
C
OUT
10A
680碌F
6.3V
+
V
OSENSE
PGND
C
VCC
4.7碌F
1775 F01
Figure 1. High Efficiency Step-Down Converter
U
Efficiency vs Load Current
100
95
90
85
80
75
70
0.01
V
IN
= 10V
f = 150kHz
FCB = INTV
CC
V
OUT
= 5V
V
OUT
= 3.3V
0.1
1
LOAD CURRENT (A)
10
1775 F01b
U
U
1