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PDF LT1949EMS8 Data sheet ( Hoja de datos )
| Número de pieza | LT1949EMS8 | |
| Descripción | 600kHz/ 1A Switch PWM DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s 1A, 0.5Ω, 30V Internal Switch
s Operates with VIN as Low as 1.5V
s 600kHz Fixed Frequency Operation
s Low-Battery Detector Stays Active in Shutdown
s Low VCESAT Switch: 410mV at 800mA
s Pin-for-Pin Compatible with the LT1317B
s Small 8-Lead MSOP and SO Packages
U
APPLICATIO S
s LCD Bias Supplies
s GPS Receivers
s Battery Backup
s Portable Electronic Equipment
s Diagnostic Medical Instrumentation
LT1949
600kHz, 1A Switch
PWM DC/DC Converter
DESCRIPTIO
The LT®1949 is a fixed frequency step-up DC/DC con-
verter with a 1A, 0.5Ω internal switch. Capable of gener-
ating 10V at 175mA from a 3.3V input, the LT1949 is ideal
for generating bias voltages for large screen LCD panels.
Constant frequency 600kHz operation results in a low
noise output that is easy to filter and the 30V switch rating
allows output voltage up to 28V using a single inductor. An
external compensation pin gives the user flexibility in
optimizing loop compensation, allowing small low ESR
ceramic capacitors to be used at the output. The 8-lead
MSOP and SO packages ensure a low profile overall
solution.
The LT1949 includes a low-battery detector that stays
alive when the device goes into shutdown. Quiescent
current in shutdown is 25µA, while operating current is
4.5mA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
3.3V
+
C1
22µF
SHUTDOWN
L1
10µH
VIN SW
LT1949
SHDN
FB
VC GND
68k
330pF
D1
R1
1M
R2
140k
VOUT
10V
175mA
C2
10µF
CERAMIC
C1: AVX TAJA226M006R
C2: TAIYO YUDEN LMK325BJ106MN
D1: MBRM120LT3
L1: SUMIDA CDRH62B-100
1949 F01
Figure 1. 3.3V to 10V/175mA DC/DC Converter
90
VOUT = 10V
80
70
3.6VIN 4.2VIN 3VIN
60
50
40
30
20
5
10 50 100
LOAD CURRENT (mA)
300
1949 F02
Figure 2. 3.3V to 10V Converter Efficiency
1
1 page  
BLOCK DIAGRA
LT1949
1.24V
REFERENCE
FB
2
VOUT
R1
(EXTERNAL)
FB
R2
(EXTERNAL)
+
gm
–
ERROR
AMPLIFIER
RAMP
GENERATOR
600kHz
OSCILLATOR
LBI
VC
7+
LBO
18
– A4
200mV
+
ENABLE
SHDN
BIAS –
A1
COMPARATOR
SHUTDOWN
3
SW
–
FF
+
Σ
+
RQ
S
+ A2
COMPARATOR
DRIVER
5
Q3
+
A=2
–
0.06Ω
4
GND 1949 BD
Figure 3. LT1949 Block Diagram
U
OPERATIO
The LT1949 is a current mode, fixed frequency step-up
DC/DC converter with an internal 1A NPN power transis-
tor. Operation can best be understood by referring to the
Block Diagram.
At the beginning of each oscillator cycle, the flip-flop is set
and the switch is turned on. Current in the switch ramps
up until the voltage at A2’s positive input reaches the VC
pin voltage, causing A2’s output to change state and the
switch to be turned off. The signal at A2’s positive input is
a summation of a signal representing switch current and
a ramp generator (introduced to avoid subharmonic oscil-
lations at duty factors greater than 50%). If the load
increases, VOUT (and FB) will drop slightly and the error
amplifier will drive VC to a higher voltage, causing current
in the switch to increase. In this way, the error amplifier
drives the VC pin to the voltage necessary to satisfy the
load. Frequency compensation is provided by an external
series RC network connected between the VC pin and
ground.
Layout Hints
The LT1949 switches current at high speed, mandating
careful attention to layout for proper performance. You
will not get advertised performance with careless layouts.
Figure 4 shows recommended component placement for
a boost (step-up) converter. Follow this closely in your PC
layout. Note the direct path of the switching loops. Input
capacitor C1 must be placed close (< 5mm) to the IC
package. As little as 10mm of wire or PC trace from CIN to
VIN will cause problems such as inability to regulate or
oscillation.
The ground terminal of output capacitor C2 should tie
close to Pin 4 of the LT1949. Doing this reduces dI/dt in the
ground copper which keeps high frequency spikes to a
minimum. The DC/DC converter ground should tie to the
PC board ground plane at one place only, to avoid intro-
ducing dI/dt in the ground plane.
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT1949EMS8.PDF ] | |
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