lt1432 Linear Technology Corporation, lt1432 Datasheet

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lt1432

Manufacturer Part Number
lt1432
Description
3.3v High Efficiency Step-down Switching Regulator Controller
Manufacturer
Linear Technology Corporation
Datasheet

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FEATURE
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Burst Mode is a trademark of Linear Technology Corporation.
A
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TYPICAL
Contact Linear Technology for Potential Replacement
PPLICATI
, LTC and LT are registered trademarks of Linear Technology Corporation.
Accurate Preset 3.3V Output
Up to 87% Efficiency
Optional Burst Mode
Can Be Used with Many LTC Switching ICs
Accurate Ultra-Low-Loss Current Limit
Operates with Inputs from 4.5V to 30V
Shutdown Mode Draws Only 15µA
Uses Small 30µH Inductor
Laptop and Palmtop Computers
Portable Data-Gathering Instruments
V
IN
FOR INFORMATION PURPOSES ONLY
<0.3V = NORMAL MODE
>2.5V = SHUTDOWN
OPEN = Burst Mode
+
C1
330µF
35V
OPERATION
MODE LOGIC
S
A
MBR330p
OBSOLETE:
C6
0.02µF
Figure 1. High Efficiency 5V Buck Converter
220pF
O
PPLICATI
D1
U
FB
V
SW
V
FOR CIRCUITS WHICH DO NOT USE
Burst Mode OPERATION, C5 MAY
BE PARALLEL WITH A 680Ω, 0.1µF
IN SERIES TO GIVE WIDE PHASE MARGIN
WITH DIFFERENT SWITCHING ICs AND
OUTPUT CAPACITORS
S
C
TM
1N5818
V
LT1271
MODE
Operation for Light Loads
IN
D2
V
C
0.03µF
C5
O
DIODE
LT1432-3.3
GND
V
IN
GND
TANT
U
10µF
C3
+
V
V
V
LIM
OUT
+
30µH
L1
***MAXIMUM CURRENT IS DETERMINED
D2**
**OPTIONAL CONNECTION FOR D2.
*R2 IS MADE FROM PC BOARD
EFFICIENCY IS HIGHER, BUT MINIMUM
INFORMATION SECTION.
COPPER TRACES.
BY THE CHOICE OF LT1071 FAMILY MAIN SWITCHER IC.
SEE APPLICATION INFORMATION SECTION.
IN
INCREASES. SEE APPLICATION
0.013Ω
R2*
V
100µF
10µH
3A
+
16V
3.3V High Efficiency Step-Down
+
×
C2
390µF
16V
Switching Regulator Controller
D
The LT
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.
OPTIONAL
OUTPUT
FILTER
V
3.3V
3A
ESCRIPTIO
LT1432-3.3 TA01
OUT
***
®
1432-3.3 is a control chip designed to operate
U
100
90
80
70
60
0
0
LT1271, L = 30µH
V
IN
= 7V
D2 CONNECTED
TO INPUT
20mA
1A
Efficiency
D2 CONNECTED
TO OUTPUT
LT1432-3.3
Burst Mode OPERATION
(USE mA SCALE)
40mA
2A
LT1432-3.3 TA02
60mA
3A
1

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lt1432 Summary of contents

Page 1

... 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. 10µH ...

Page 2

... 1.5V (Forced 26V, OUT – 1V – 1. (Note 150 A to 250 TOP VIEW ORDER PART NUMBER 8 MODE 7 GND LT1432CN8-3 LT1432CS8-3.3 5 DIODE S8 PACKAGE 8-LEAD PLASTIC SO = 150 C/W (N8 170 C/W (S8) JA MIN TYP MAX 3.24 3.30 3. 0.3 0.5 0.9 1 0.6 0.9 1.5 0.25 0.45 0.45 0.8 1 ...

Page 3

... SW IN LT1271 FB V GND DIODE S1** S2** MODE CONTROL 8 Figure 2 LT1432-3.3 MIN TYP 1.6 80 120 3.0 4.5 4 < OUT 30 pin switched from 3.6V to 3.0V. OPTIONAL CONNECTION OUT LIM 1 2 60mV + – + – 7 MODE GND LT1432-3.3 F02 MAX UNITS 2 p ...

Page 4

... Input Voltage 5 5.0 4.5 4.0 3 LOAD CURRENT (mA) LT1432-3.3 G05 Current Limit Sense Voltage 100 0 25 JUNCTION TEMPERATURE ( C) LT1432-3.3 G08 * TEMPERATURE COEFFICIENT OF SENSE VOLTAGE IS DESIGNED TO TRACK COPPER RESISTANCE. LT1270 LT1432-3.3 G03 40 50 LT1432-3.3 G06 75 100 LT1432-3.3 G9 ...

Page 5

... MODE PIN VOLTAGE (V) LT1432-3.3 G14 Start-up Switch Characteristics NOTE VERTICAL AND HORIZONTAL SCALE CHANGES AT 0,0 –20 –40 –60 –80 –2 – 100 + VOLTAGE IN LT1432-3.3 G16 to V OUT C 75 100 LT1432-3.3 G12 8 10 LT1432-3.3 G15 20 30 LT1432-3.3 G18 5 ...

Page 6

... A floating power supply for the switcher is generated by D2 and C3 which peak detect the input voltage during switch off time. This is different than the 5V version of the LT1432 which connects the anode of the diode to the output rather than the input. The output connection is more efficient because the floating voltage is a constant 5V (or 3 ...

Page 7

... D1, L1 and C2 act as the conventional catch diode and output filter of the buck converter. These components should be selected carefully to maintain high efficiency and acceptable output ripple. See the original LT1432 (5V) data sheet for detailed discussions of these parts. Current limiting is performed by R2. Sense voltage is only 60mV to maintain high efficiency ...

Page 8

... Full Shutdown When the Mode pin is driven high, full shutdown of the regulator occurs. Regulator input current will then consist of the LT1432 shutdown current ( 15 A) plus the switch leakage of the switching A). Mode input current ( 5V) must also be considered. Start-up ...

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