LTC1778EGN Datasheet, PDF (1/24 Pages) Linear Technology – Wide Operating Range, No RSENSE Step-Down Controller

LTC1778/LTC1778-1
Wide Operating Range,
No R_SENSE^TM Step-Down Controller
FEATURES
■ _{No Sense Resistor Required}
■ _{True Current Mode Control}
■ _{Optimized for High Step-Down Ratios}
■ _{tON(MIN) ≤ 100ns}
■ _{Extremely Fast Transient Response}
■ _{Stable with Ceramic COUT}
■ _{Dual N-Channel MOSFET Synchronous Drive}
■ _{Power Good Output Voltage Monitor (LTC1778)}
■ _{Adjustable On-Time (LTC1778-1)}
■ _{Wide VIN Range: 4V to 36V}
■ _{±1% 0.8V Voltage Reference}
■ _{Adjustable Current Limit}
■ _{Adjustable Switching Frequency}
■ _{Programmable Soft-Start}
■ _{Output Overvoltage Protection}
■ _{Optional Short-Circuit Shutdown Timer}
■ _{Micropower Shutdown: IQ < 30µA}
■ _{Available in a 16-Pin Narrow SSOP Package}
U
APPLICATIO S
■ _{Notebook and Palmtop Computers}
■ _{Distributed Power Systems}
DESCRIPTIO
The LTC^®1778 is a synchronous step-down switching
regulator controller optimized for CPU power. The con-
troller uses a valley current control architecture to deliver
very low duty cycles with excellent transient response
without requiring a sense resistor. Operating frequency is
selected by an external resistor and is compensated for
variations in V_IN.
Discontinuous mode operation provides high efficiency
operation at light loads. A forced continuous control pin
reduces noise and RF interference, and can assist second-
ary winding regulation by disabling discontinuous opera-
tion when the main output is lightly loaded.
Fault protection is provided by internal foldback current
limiting, an output overvoltage comparator and optional
short-circuit shutdown timer. Soft-start capability for sup-
ply sequencing is accomplished using an external timing
capacitor. The regulator current limit level is user program-
mable. Wide supply range allows operation from 4V to 36V
at the input and from 0.8V up to (0.9)V_IN at the output.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R_SENSE is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6100678, 6580258, 5847554, 6304066
TYPICAL APPLICATIO
C_SS
0.1µF
C_C
500pF
R_C
20k
I_ON
V_IN
RUN/SS TG
SW
I_TH
BOOST
LTC1778
SGND INTV_CC
BG
PGOOD PGND
R_ON
1.4MΩ
C_B 0.22µF
D_B
CMDSH-3
+ _CVCC
4.7µF
M1
Si4884 L1
1.8µH
M2
Si4874
D1
B340A
C_IN
10µF
V_IN
5V TO 28V
50V
×3
V_OUT
2.5V
+ ^{COUT 10A}
180µF
4V
×2
R2
30.1k
V_FB
R1
14k
1778 F01a
Figure 1. High Efficiency Step-Down Converter
Efficiency vs Load Current
100
V_OUT = 2.5V
V_IN = 5V
90
V_IN = 25V
80
70
60
0.01
0.1
1
LOAD CURRENT (A)
10
1778 F01b
1778fb
1