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PDF LT1302CN8 Data sheet ( Hoja de datos )
| Número de pieza | LT1302CN8 | |
| Descripción | Micropower High Output Current Step-Up Adjustable and Fixed 5V DC/DC Converters | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s 5V at 600mA or 12V at 120mA from 2-Cell Supply
s 200µA Quiescent Current
s Logic Controlled Shutdown to 15µA
s Low VCESAT Switch: 310mV at 2A Typical
s Burst ModeTM Operation at Light Load
s Current Mode Operation for Excellent
Line and Load Transient Response
s Available in 8-Lead SO or PDIP
s Operates with Supply Voltage as Low as 2V
APPLICATI S
s Notebook and Palmtop Computers
s Portable Instruments
s Personal Digital Assistants
s Cellular Telephones
s Flash Memory
LT1302/LT1302-5
Micropower
High Output Current
Step-Up Adjustable and
Fixed 5V DC/DC Converters
DESCRIPTIO
The LT®1302/LT1302-5 are micropower step-up DC/DC
converters that maintain high efficiency over a wide
range of output current. They operate from a supply
voltage as low as 2V and feature automatic shifting
between Burst Mode operation at light load, and current
mode operation at heavy load.
The internal low loss NPN power switch can handle
current in excess of 2A and switch at frequencies up to
400kHz. Quiescent current is just 200µA and can be
further reduced to 15µA in shutdown.
Available in 8-pin PDIP or 8-pin SO packaging, the LT1302/
LT1302-5 have the highest switch current rating of any
similarly packaged switching regulators presently on the
market.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATI
L1
10µH
2 CELLS
+ C1
100µF
C3
0.1µF
D1
+ C2
100µF
NC
65
7
VIN
SW
IT 3
SHDN SHUTDOWN
LT1302-5
8 PGND SENSE 4
GND VC
12
RC
20k
CC
0.01µF
OUTPUT
5V
600mA
C1 = C2 = SANYO OS-CON
L1 = COILTRONICS CTX10-3
COILCRAFT DO3316-103
LT1302 • F01
D1 = MOTOROLA MBRS130LT3
Figure 1. 2-Cell to 5V/600mA DC/DC Converter
2-Cell to 5V Converter Efficiency
90
88
86 VIN = 3V
84
VIN = 2.5V
82
80 VIN = 2V
78
76
74
72
70
1
10 100
LOAD CURRENT (mA)
1000
LT1302 • TA02
1
1 page  
LT1302/LT1302-5
PI FU CTIO S
SW (Pin 7): Switch Pin. Connect inductor and diode here.
Keep layout short and direct.
PGND (Pin 8): Power Ground. Pins 8 and 1 should be
connected under the package. In the SO package, pins 1
and 8 are thermally connected to the die. One square inch
of PCB copper provides an adequate heat sink for the
device.
BLOCK DIAGRA SM
VIN
+
C1
C5
100pF
1.24V
REFERENCE
R1
FB
4
R2
SHDN
3 SHUTDOWN
L1
6
VIN
C2
0.1µF
+
–
VOS
15mV
CMP1
ENABLE
OFF
220kHz
OSCILLATOR
HYSTERETIC
COMPARATOR 2µA
VIN
Q5
–
A1
+
ERROR
AMPLIFIER
+
A2
–
36mV
R5
730Ω
A3
DRIVER
VIN
Q1 Q2
BIAS
300Ω 3.6k
D1
+
VOUT
C3
7
SW
R4
1.75Ω
Q3 Q4
160X
GND
1
2 VC
R3
22k
C4
0.01µF
5 IT
PGND
8
1302 F02
Figure 2. LT1302 Block Diagram
5
5 Page 
LT1302/LT1302-5
APPLICATIONS INFORMATION
ally reaches audio frequencies, but at a much lighter load
than without the IT feature. At some input voltage/load
current combinations, some residual bursting may occur
at frequencies out of the audio band.
VOUT
100mV/DIV
AC COUPLED
INDUCTOR
CURRENT
1A/DIV
ILOAD
525mA
25mA
1ms/DIV
1302 F08b
Figure 8b. 3.3k Resistor from IT Pin to Ground Forces
LT1302 into Current Mode Regardless of Load. Audio
Frequency Component Eliminated
90
IT FLOATING
80
70
3.3k IT TO GND
60
50
40
30
1
10 100
OUTPUT CURRENT (mA)
1000
1302 F08c
Figure 8c. 3.3k Resistor for IT to Ground Increases
Efficiency at Moderate Load, Decreases at Light Load
The IT pin cannot be used as a soft-start. Large capacitors
connected to the pin will cause erratic operation. If oper-
ating the device in Burst Mode, let the pin float. Keep high
dV/dt signals away from the pin.
Figure 8c details efficiency with and without the addition of
R1. Burst Mode operation keeps efficiency high at light
load with IT floating. Efficiency falls off at light load with
R1 added because the LT1302 cannot transition into Burst
Mode.
Layout
The high speed, high current switching associated with
the LT1302 mandates careful attention to layout. Follow
the suggested component placement in Figure 9 for proper
operation. High current functions are separated by the
package from sensitive control functions. Feedback resis-
tors R1 and R2 should be close to the feedback pin (pin4).
Noise can easily be coupled into this pin if care is not taken.
A small capacitor (100pF to 200pF) from FB to ground
provides a high frequency bypass. If the LT1302 is oper-
ated off a three-cell or higher input, R3 (2Ω to 10Ω) in
series with VIN is recommended. This isolates the device
from noise spikes on the input supply. Do not put in R3 if
the device must operate from a 2V input, as input current
will cause the voltage at the LT1302’s VIN pin to go below
2V. The 0.1µF ceramic bypass capacitor C3 (use X7R, not
Z5U) should be mounted as close as possible to the
package. When R3 is used, C3 should be a 1µF tantalum
unit. Grounding should be segregated as illustrated. C3’s
ground trace should not carry switch current. Run a
VIN
VOUT
L1
D1
C2
R3
2Ω
+
C1
C3 5
6
7
8
LT1302
4
3 R1
2
1
R2
200pF
RC
SHUTDOWN
CC
GND (BATTERY AND LOAD RETURN)
Figure 9. Suggested Component Placement for LT1302
1302 F09
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1302CN8.PDF ] | |
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