LT1959 Datasheet, PDF (1/24 Pages) Linear Technology – 4.5A, 500kHz Step-Down Switching Regulator

LT1959
4.5A, 500kHz Step-Down
Switching Regulator
FEATURES
s _{Operates with Input as Low as 4V}
s _{Output Range Down to 1.21V}
s _{Constant 500kHz Switching Frequency}
s _{Uses All Surface Mount Components}
s _{Inductor Size Reduced to 1.8µH}
s _{Saturating Switch Design: 0.07Ω}
s _{Shutdown Current: 20µA}
s _{Easily Synchronizable}
s _{Cycle-by-Cycle Current Limiting}
s _{4.5A Switch}
s _{Current Mode Control}
U
APPLICATIO S
s _{Portable Computers}
s _{Battery-Powered Systems}
s _{Battery Chargers}
s _{Distributed Power}
s _{5V to 3.3V Conversion}
s _{5V to 2.5V Conversion}
s _{5V to 1.8V Conversion}
DESCRIPTIO
The LT^®1959 is a 500kHz monolithic buck mode switching
regulator functionally identical to the LT1506 but optimized
for lower output voltage applications. It will operate down
to 1.21V output compared to 2.42V for the LT1506. A 4.5A
switch is included on the die along with all the necessary
oscillator, control and logic circuitry. High switching fre-
quency allows a considerable reduction in the size of ex-
ternal components. The topology is current mode for fast
transient response and good loop stability.
A special high speed bipolar process and new design tech-
niques achieve high efficiency at high switching frequency.
Efficiency is maintained over a wide output current range
by keeping quiescent supply current to 4mA and by utiliz-
ing a supply boost capacitor to saturate the power switch.
The LT1959 fits into standard 7-pin DD and fused lead
SO-8 packages. Full cycle-by-cycle short-circuit protection
and thermal shutdown are provided. Standard surface
mount external parts are used, including the inductor and
capacitors. There is the optional function of shutdown or
synchronization. A shutdown signal reduces supply current
to 20µA. Synchronization allows an external logic level sig-
nal to increase the internal oscillator from 580kHz to 1MHz.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
INPUT
5V
10µF
C3
TO
+
50µF
CERAMIC
5V to 1.8V Down Converter
D2
1N914
OPEN
OR
HIGH
= ON
BOOST
V_IN
V_SW
LT1959
SHDN
FB
GND V_C
C_C
1.5nF
C2
0.68µF
L1
5µH
R1
1.21k
OUTPUT
1.8V
4A
R2 ⁺
D1
2.49k
MBRS330T3
C1
100µF, 10V
SOLID
TANTALUM
1959 TA01
Efficiency vs Load Current
90
V_OUT = 3.3V
V_IN = 5V
L = 10µH
85
80
75
70
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
LOAD CURRENT (A)
1959 TA02
1