LM3509SDX National Semiconductor Corporation, LM3509SDX Datasheet - Page 20

• Manufacturer Part Number: LM3509SDX
• Description: High Efficiency Boost For White Led S And/or Oled Displays With Dual Current Sinks And I2c Compatible Brightness Control
• Manufacturer: National Semiconductor Corporation

www.national.com
TABLE 7. Recommended Output Capacitors
INDUCTOR SELECTION
The LM3509 is designed for use with a 10µH inductor, how-
ever 22µH are suitable providing the output capacitor is in-
creased 2×'s. When selecting the inductor ensure that the
saturation current rating (I
enough and the inductor is large enough such that at the
maximum LED current the peak inductor current is less than
the LM3509’s peak switch current limit. This is done by choos-
ing:
TABLE 8. Recommended Inductors
DIODE SELECTION
The output diode must have a reverse breakdown voltage
greater than the maximum output voltage. The diodes aver-
age current rating should be high enough to handle the
LM3509’s output current. Additionally, the diodes peak cur-
rent rating must be high enough to handle the peak inductor
current. Schottky diodes are recommended due to their lower
TABLE 9. Recommended Schottky Diodes
Manufacturer
ON Semiconductor
Manufacturer
Manufacturer
Diodes Inc.
TOKO
TDK
TDK
Murata
Murata
Philips
TDK
TDK
VLF3012AT-100M
VLF4012AT-100M
A997AS-100M
Part Number
SAT
GRM39X5R105K25D53
GRM219R61E225KA12
C1608X5R1E105M
C2012X5R1E225M
) for the chosen inductor is high
R49
R79
NSR0320MW2T
Part Number
Part Number
B05030WS
BAT760
9
Value
10µH
10µH
10µH
Package
SOD-323
SOD-323
SOD-323
Value
2.2µF
2.2µF
1µF
1µF
20
3.5mm×3.7mm×1.
3.8mm×3.8mm×1.
2.6mm×2.8mm×1
Dimensions
Values for I
vs. V
Table 8 shows possible inductors, as well as their corre-
sponding case size and their saturation current ratings.
forward voltage drop (0.3V to 0.5V) compared to (0.6V to
0.8V) for PN junction diodes. If a PN junction diode is used,
ensure it is the ultra-fast type (trr < 50ns) to prevent excessive
loss in the rectifier. For Schottky diodes the B05030WS (or
equivalent) work well for most designs. See Table 9 for a list
of other Schottky Diodes with similar performance.
2mm
8mm
mm
IN
Reverse Breakdown
in the Typical Performance Characteristics graphs.
PEAK
Voltage
30V
23V
30V
can be found in the plot of peak current limit
Case Size
0603
0603
0805
0805
490mA
800mA
580mA
I
SAT
Average Current Rating
Voltage Rating
DC Resistance
0.5A
0.36Ω
0.18Ω
1A
1A
25V
25V
25V
25V
0.3Ω