LT1432-3.3_15 Datasheet, PDF (1/8 Pages) Linear Technology – 3.3V High Efficiency Step-Down Switching Regulator Controller

OBSOLETE:
FOR INFORMATION PURPOSES ONLY
Contact Linear Technology for Potential Replacement
FEATURES
I _{Accurate Preset 3.3V Output}
I _{Up to 87% Efficiency}
I _{Optional Burst Mode}^TM _{Operation for Light Loads}
I _{Can Be Used with Many LTC Switching ICs}
I _{Accurate Ultra-Low-Loss Current Limit}
I _{Operates with Inputs from 4.5V to 30V}
I _{Shutdown Mode Draws Only 15µA}
I _{Uses Small 30µH Inductor}
APPLICATI S
I _{Laptop and Palmtop Computers}
I _{Portable Data-Gathering Instruments}
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
LT1432-3.3
3.3V High Efficiency Step-Down
Switching Regulator Controller
DESCRIPTIO
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
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 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.
TYPICAL APPLICATI
D2
1N5818
V_IN
+
C1
330µF
35V
V_SW
FB
V_C
C6
0.02µF
V_IN
LT1271
GND
D2**
10µH
3A
+
100µF
16V
OPTIONAL
OUTPUT
FILTER
D1
MBR330p
C5^†
0.03µF
C3 +
10µF
TANT
V_C DIODE
L1
30µH
V⁺
R2*
0.013Ω
+
×
V_OUT***
3.3V
C2 ^3A
390µF
16V
V_IN
V_LIM
LT1432-3.3
MODE LOGIC
220pF
<0.3V = NORMAL MODE
>2.5V = SHUTDOWN
OPEN = Burst Mode
OPERATION
MODE
V_OUT
GND
*R2 IS MADE FROM PC BOARD
COPPER TRACES.
†_{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
IN ^{INCREAVSES. SEE APPLICATION}
INFORMATION SECTION.
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.
OUTPUT CAPACITORS
SEE APPLICATION INFORMATION SECTION.
LT1432-3.3 TA01
Figure 1. High Efficiency 5V Buck Converter
Efficiency
100
LT1271, L = 30µH
V_IN = 7V
D2 CONNECTED
90
TO OUTPUT
D2 CONNECTED
80
TO INPUT
70
Burst Mode OPERATION
(USE mA SCALE)
60
0
0
1A
20mA
2A
40mA
3A
60mA
LT1432-3.3 TA02
1