s Accurate Preset 3.3V Output
s Up to 87% Efficiency
s Optional Burst ModeTM Operation for Light Loads
s Can Be Used with Many LTC Switching ICs
s Accurate Ultra-Low-Loss Current Limit
s Operates with Inputs from 4.5V to 30V
s Shutdown Mode Draws Only 15µA
s Uses Small 30µH Inductor
s Laptop and Palmtop Computers
s Portable Data-Gathering Instruments
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
3.3V High Efficiency Step-Down
Switching Regulator Controller
The LT®1432-3.3 is a control chip designed to operate
with the LT1171/LT1271 family of switching regulators to
make a very high efficiency 3.3V step-down (buck) switch-
ing regulator. A minimum of external components is
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 4.5V input.
The LT1432-3.3 has a logic controlled Burst Mode operation
to achieve high efficiency at very light load currents (0mA to
100mA) such as memory keep-alive. In normal switching
mode, the standby power loss is about 30mW, limiting
efficiency at light loads. In Burst Mode operation, standby
loss is reduced to approximately 11mW. Output current in
this mode is typically in the 5mA to 100mA range.
The LT1432-3.3 is available in 8-pin SO and PDIP pack-
ages. The LT1171/LT1271 is also available in surface
mount DD packages.
<0.3V = NORMAL MODE
>2.5V = SHUTDOWN
OPEN = Burst Mode
*R2 IS MADE FROM PC BOARD
†FOR CIRCUITS WHICH DO NOT USE
**OPTIONAL CONNECTION FOR D2.
EFFICIENCY IS HIGHER, BUT MINIMUM
Burst Mode OPERATION, C5 MAY
BE PARALLEL WITH A 680Ω, 0.1µF
V IN INCREASES. SEE APPLICATION
IN SERIES TO GIVE WIDE PHASE MARGIN ***MAXIMUM CURRENT IS DETERMINED
WITH DIFFERENT SWITCHING ICs AND
BY THE CHOICE OF LT1071 FAMILY MAIN SWITCHER IC.
SEE APPLICATION INFORMATION SECTION.
Figure 1. High Efficiency 5V Buck Converter
LT1271, L = 30µH
VIN = 7V
90 TO OUTPUT
80 TO INPUT
Burst Mode OPERATION
(USE mA SCALE)