LT1432 Datasheet, PDF (1/28 Pages) Linear Technology – 5V High Efficiency Step-Down Switching Regulator Controller

LT1432
5V High Efficiency Step-Down
Switching Regulator Controller
FEATURES
s _{Accurate Preset +5V Output}
s _{Up to 90% Efficiency}
s _{Optional Burst Mode for Light Loads}
s _{Can be Used with Many LTC Switching ICs}
s _{Accurate Ultra-Low-Loss Current Limit}
s _{Operates with Inputs from 6V to 30V}
s _{Shutdown Mode Draws Only 15µA}
s _{Uses Small 50µH Inductor}
APPLICATI S
s _{Laptop and Palmtop Computers}
s _{Portable Data-Gathering Instruments}
s _{DC Bus Distribution Systems}
s _{Battery-Powered Digital Widgets}
DESCRIPTIO
The LT1432 is a control chip designed to operate with the
LT1170/LT1270 family of switching regulators to make a
very high efficiency 5V step-down (buck) switching regula-
tor. A minimum of external components is needed.
Included is an accurate current limit which uses only 60mV
sense voltage and uses “free” PC board trace material for
the sense resistor. Logic controlled electronic shutdown
mode draws only 15µA battery current. The switching
regulator operates down to 6V input.
The LT1432 has a logic controlled “burst” mode to achieve
high efficiency at very light load currents (0 to 100mA) such
as memory keep-alive. In normal switching mode, the
standby power loss is about 60mW, limiting efficiency at
light loads. In burst mode, standby loss is reduced to
approximately 15mW. Output current in this mode is
typically in the 5mA to 100mA range.
The LT1432 is available in 8-pin surface mount and DIP
packages. The LT1170/LT1270 family will also be available
in a surface mount version of the 5-pin TO-220 package.
For 3.3V versions contact Linear Technology Corporation.
TYPICAL APPLICATI
V_IN
+
C1
330µF
35V
V_SW
V_IN
LT1170
LT1271
FB
V_C
GND
C6
0.02µF
C4
0.1µF
R1
680Ω
C5
0.03µF
C3 +
4.7µF
TANT
D1
MBR330p
V_C DIODE
D2
1N4148
10µH
3A
+
100µF
16V
OPTIONAL
OUTPUT
FILTER
L1
50µH
V⁺
R2*
0.013Ω
+
×
V_OUT
5V
C2 ^3A**
390µF
16V
V_IN
V_LIM
LT1432
MODE LOGIC
220pF
<0.3V = NORMAL MODE
>2.5V = SHUTDOWN
OPEN = BURST MODE
MODE
V_OUT
GND
* R2 IS MADE FROM PC BOARD
COPPER TRACES.
** MAXIMUM CURRENT IS DETERMINED
BY THE CHOICE OF LT1070 FAMILY.
SEE APPLICATION SECTION.
LT1432 TA01
Figure 1. High Efficiency 5V Buck Converter
100
90
80
70
60
0
0
Efficiency
NORMAL MODE
(USE AMPS SCALE)
BURST MODE
(USE mA SCALE)
1A
20mA
LT1271, L = 50µH
2A
40mA
3A
60mA
LT1432 TA02
1