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PDF LT1432-3.3 Data sheet ( Hoja de datos )
| Número de pieza | LT1432-3.3 | |
| Descripción | 3.3V High Efficiency Step-Down Switching Regulator Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
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
APPLICATI S
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.
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
VIN
+
C1
330µF
35V
VSW
C6
0.02µF
FB
VC
D1
MBR330p
LT1271
VIN
GND
C5†
0.03µF
C3 +
10µF
TANT
VC DIODE
D2**
10µH
3A
+
100µF
16V
OPTIONAL
OUTPUT
FILTER
L1
30µH
V+
R2*
0.013Ω
+
× VOUT***
3.3V
C2 3A
390µF
16V
MODE LOGIC
220pF
<0.3V = NORMAL MODE
>2.5V = SHUTDOWN
OPEN = Burst Mode
OPERATION
VIN
MODE
LT1432-3.3
VLIM
VOUT
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
V IN INCREASES. 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
VIN = 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
1 page  
LT1432-3.3
TYPICAL PERFOR A CE CHARACTERISTICS
Incremental Battery Current * in
Burst Mode Operation
2.0
TJ = 25°C
1.5
1.0
0.5
No Load Battery Current in Burst
Mode Operation
5
TJ = 25°C
4
3
2
1
Transconductance – VOUT to VC
Current
5000
4000
Gm = ∆I(VC PIN)
∆VOUT
3000
2000
0
0 5 10 15 20 25
BATTERY VOLTAGE (V)
LT1432-3.3 G10
* TO CALCULATE TOTAL BATTERY CURRENT IN Burst
Mode OPERATION, MULTIPLY LOAD CURRENT BY
INCREMENTAL FACTOR AND ADD NO-LOAD CURRENT.
0
0
5 10 15 20
BATTERY VOLTAGE (V)
25
LT1432-3.3 G11
Line Regulation
40
TJ = 25°C
20
Burst Mode Operation Load
Regulation
25
TJ = 25°C
VIN = 7V
0
NORMAL MODE
0
–25
Burst Mode OPERATION
–20 –50
–40
0
5 10 15
INPUT VOLTAGE (V)
20
LT1432-3.3 G13
Restart Load Current
40
VOUT = 4.5V
30
–75
0
20 40 60 80
LOAD CURRENT (mA)
100
LT1432-3.3 G14
Restart Time Delay
4
3
20 2
10 1
1000
0
25 50 75
JUNCTION TEMPERATURE (°C)
100
LT1432-3.3 G12
Mode Pin Current
60
TJ = 25°C
40
20
0
–20
–40
0
MODE DRIVE MUST
SINK ≈ 30µA AT 0V
2 4 68
MODE PIN VOLTAGE (V)
10
LT1432-3.3 G15
Start-up Switch Characteristics
5
TJ = 25°C
0 NOTE VERTICAL AND
HORIZONTAL SCALE
CHANGES AT 0,0
–20
–40
–60
0
0 25 50 75 100
JUNCTION TEMPERATURE (°C)
LT1432-3.3 G16
0
0 25 50 75 100
JUNCTION TEMPERATURE (°C)
LT1432-3.3 G16
–80
–2
–1 0 10 20
V+ TO VIN VOLTAGE
30
LT1432-3.3 G18
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT1432-3.3.PDF ] | |
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