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PDF FSP3307 Data sheet ( Hoja de datos )
| Número de pieza | FSP3307 | |
| Descripción | White LED Step-Up Converter | |
| Fabricantes | Linear | |
| Logotipo |  |
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FSP3307
WHITE LED STEP-UP CONVERTER
FEATURES
s Inherently Matched LED Current
s Drives Up to 8 LEDs from a 3.6V Supply
s No External Schottky Diode Required
s 1.2MHz Switching Frequency
s Automatic Soft-Start
s Open LED Protection
s High Efficiency: 81%
s Requires Only 0.22uF Output Capacitor
s Low Profile (1mm) SOT-23 Packaging
APPLICATION
s Cellular Phones
s PDAs, Handheld Computers
s Digital Cameras
s MP3 Players
s GPS Receivers
DESCRIPTIO
The FSP3307 IS step-up DC/DC converters
designed to drive up to six LEDs in series from a Li-Ion cell.
Series connection of the LEDs provides identical LED
currents and eliminates the need for ballast resistors.
These devices integrate the Schottky diode required exter-
nally on competing devices. Additional features include
output voltage limiting when LEDs are disconnected, one-
pin shutdown and dimming control. The FSP3307has
internal soft-start.
TheFSP3307switches at 1.2MHz, allowing the use of tiny
external components. Constant frequency switching
results in low input noise and a small output capacitor.
Just 0.22µF is required for 4-, 6- or 8-LED applications.
The FSP3307 is available in low profile(1mm)6-lead
TYPICAL APPLICATION
FSP3307
Figure 1. Li-Ion Powered Driver for Eight White LEDs
Conversion Efficiency
82 VIN = 3.6V
80 4 LEDs
78
76
74
72
70
68
66
64
62
60
0 5 10 15
LED CURRENT (mA)
20
1
1 page  
BLOCK DIAGRAM
VIN
5
VREF
1.25V
FB
3
200mV
–
+ A1
+
CTRL
4
40k
10k
– COMPARATOR
RC
A2
+
RQ
S
CC
Σ
RAMP
GENERATOR
1.2MHz*
OSCILLATOR
DRIVER
+
–
6 SW
VOUT
1
Q1
OVERVOLTAGE
PROTECT
0.2Ω
2 GND
Figure 2. FSP3307 Block Diagram
APPLICATIONS INFORMATION
Operation
The FSP3307uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. Operation can be best understood by referring to the
block diagram in Figure 2. At the start of each oscillator
cycle, the SR latch is set, which turns on the power switch
Q1. A voltage proportional to the switch current is added
to a stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the
SR latch is reset turning off the power switch. The level at
the negative input of A2 is set by the error amplifier A1,
and is simply an amplified version of the difference
between the feedback voltage and the reference voltage of
200mV. In this manner, the error amplifier sets the
correct peak current level to keep the output in regulation.
If the error amplifier’s output increases, more current is
delivered to the output; if it decreases, less current is
delivered. The CTRL pin voltage is used to adjust the
reference voltage.
result in some low frequency ripple, although the LED
current remains regulated on an average basis down to
zero. The photo in Figure 3a details circuit operation
driving three white LEDs at a 1.5mA load. Peak inductor
current is less than 40mA and the regulator operates in
discontinuous mode, meaning the inductor current
VSW
5V/DIV
IL
20mA/DIV
VOUT
10mV/DIV
VIN = 4.2V
ILED = 1.5mA
3 LEDs
0.2µs/DIV
Figure 3. Switching Waveforms
Minimum Output Current
The FSP3307can drive a 3-LED string at 1.5mA LED
current without pulse skipping. As current is further
reduced, the device will begin skipping pulses. This will
5
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PACKAGE DESCRIPTION
S6 Package
6-Lead Plastic SOT-23
(Reference LTC DWG # 05-08-1636)
0.62 0.95
MAX REF
1.22 REF
2.90 BSC
(NOTE 4)
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC 1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.20 BSC
DATUM ‘A’
0.95 BSC
0.80 – 0.90
1.00 MAX
0.30 – 0.50 REF
0.09 – 0.20
NOTE:
(NOTE 3)
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
1.90 BSC
0.30 – 0.45
6 PLCS (NOTE 3)
0.01 – 0.10
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet FSP3307.PDF ] | |
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