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PDF LT1305CS8 Data sheet ( Hoja de datos )
| Número de pieza | LT1305CS8 | |
| Descripción | Micropower High Power DC/DC Converter with Low-Battery Detector | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT1305CS8 (archivo pdf) en la parte inferior de esta página. Total 8 Páginas | ||
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FEATURES
s 5V at 400mA from 2V Input
s Supply Voltage As Low As 1.8V
s 120µA Quiescent Current
s Low-Battery Detector
s Low VCESAT Switch: 310mV at 2A Typ
s Uses Inexpensive Surface Mount Inductors
s 8-Lead SO Package
APPLICATI S
s 2-Cell and 3-Cell to 5V Conversion
s EL Panel Drivers
s Portable Instruments
LT1305
Micropower High Power
DC/DC Converter with
Low-Battery Detector
DESCRIPTIO
The LT®1305 is a micropower step-up DC/DC converter
that uses Burst ModeTM operation. Similar to the LT1303,
the LT1305 features a 2A internal low-loss switch and can
deliver up to four times the output power of the LT1303.
Quiescent current is only 120µA and the Shutdown pin
further reduces current to 10µA. A low-battery detector
provides an open-collector output that goes low when the
input voltage drops below a preset level. The LT1305 is
available in an 8-pin SO, easing board space requirements.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation
TYPICAL APPLICATI
2-Cell and 3-Cell to 5V/400mA DC/DC Converter
with Low-Battery Detect
L1
10µH
D1
2 TO 3
CELLS
316k
1%
+ C1
220µF
412k
1%
SHUTDOWN
VIN
LBI
SW
LBO
LT1305
SHDN
GND
FB
PGND
100k
301k
1%
100k C2
1% 220µF
LOW BATTERY
GOES LOW AT
VBAT = 2.2V
VOUT
5V
+ 400mA
C1, C2: AVX TPSE227010R0100
D1: MOTOROLA MBRS130LT3
L1: COILCRAFT D03316-103
LT1305 • TA03
Efficiency
90
VIN = 4.00V
80 VIN = 3.00V
VIN = 2.00V
VIN = 2.50V
70
60
1
10 100
LOAD CURRENT (mA)
1000
LT1305 • TA02
1
1 page  
LT1305
BLOCK DIAGRAM
VIN +
C5
6 VIN
L1 D1
SW
7
+
C4
CURRENT
COMPARATOR
36mV
C2
R1 HYSTERETIC
COMPARATOR
FB
4
–
OFF
R2
REFERENCE
1.24V
C1
+
OSCILLATOR
A3
DRIVER
R1
3Ω
Q2
1× Q1
160×
–
C3
+
GND
1
LBI
5
LBO
2
SHUTDOWN
3
PGND
8
Figure 1. LT1305 Block Diagram
LT1305 • F01
U
OPERATION
Operation of the LT1305 is best understood by referring to
the Block Diagram in Figure 1. When C1’s negative input,
related to the output voltage by the appropriate resistor-
divider ratio, is higher than the 1.24V reference voltage,
C1’s output is low. C2, A3 and the oscillator are turned off,
drawing no current. Only the reference and C1 consume
current, typically 120µA. When C1’s negative input drops
below 1.24V and overcomes C1’s 6mV hysteresis, C1’s
output goes high, enabling the oscillator, current compara-
tor C2 and driver A3. Quiescent current increases to 2mA
as the device goes into active switching mode. Q1 then
turns on in controlled saturation for nominally 6µs or until
current comparator C2 trips, whichever comes first. The
switch then turns off for approximately 1.5µs, then turns on
again. The LT1305’s switching causes current to alter-
nately build up in L1 and dump into output capacitor C4 via
D1, increasing the output voltage. When the output is high
enough to cause C1’s output to go high, switching action
ceases. Capacitor C4 is left to supply current to the load
until VOUT decreases enough to force C1’s output high, and
the entire cycle repeats. Figure 2 details relevant wave-
forms. C1’s cycling causes low-to-mid-frequency ripple
voltage on the output. Ripple can be reduced by making the
output capacitor large. The 220µF unit specified results in
ripple of 50mV to 100mV on the 5V output. Paralleling two
capacitors will decrease ripple by approximately 50%.
VOUT
100mV/DIV
AC COUPLED
VSW
5V/DIV
IL
1A/DIV
50µs/DIV
Figure 2. Burst Mode Operation
LT1305 • F02
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT1305CS8.PDF ] | |
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