LM3509 Datasheet, PDF(20/24 Page) National Semiconductor (TI) – OLED Displays with Dual Current Sinks and I2C Compatible Brightness Control

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LM3509 Datasheet, PDF (20/24 Pages) National Semiconductor (TI) – OLED Displays with Dual Current Sinks and I2C Compatible Brightness Control

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TABLE 7. Recommended Output Capacitors

Manufacturer

TDK

Murata

TDK

Murata

Part Number

C1608X5R1E105M

GRM39X5R105K25D53

C2012X5R1E225M

GRM219R61E225KA12

Value

1ÂµF

2.2ÂµF

Case Size

0603

0805

Voltage Rating

25V

INDUCTOR SELECTION

The LM3509 is designed for use with a 10ÂµH inductor, how-

ever 22ÂµH are suitable providing the output capacitor is in-

creased 2Ã's. When selecting the inductor ensure that the

saturation current rating (ISAT) for the chosen inductor is high

enough and the inductor is large enough such that at the

maximum LED current the peak inductor current is less than

the LM3509âs peak switch current limit. This is done by choos-

ing:

Values for IPEAK can be found in the plot of peak current limit

vs. VIN in the Typical Performance Characteristics graphs.

Table 8 shows possible inductors, as well as their corre-

sponding case size and their saturation current ratings.

TABLE 8. Recommended Inductors

Manufacturer

TDK

TOKO

Part Number

VLF3012AT-100M

R49

VLF4012AT-100M

R79

A997AS-100M

Value

10ÂµH

Dimensions

2.6mmÃ2.8mmÃ1

3.5mmÃ3.7mmÃ1.

2mm

3.8mmÃ3.8mmÃ1.

8mm

ISAT

490mA

800mA

580mA

DC Resistance

0.36â¦

0.3â¦

0.18â¦

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

LM3509âs 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

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.

TABLE 9. Recommended Schottky Diodes

Manufacturer

Diodes Inc.

Philips

ON Semiconductor

Part Number

B05030WS

BAT760

NSR0320MW2T

Package

SOD-323

Reverse Breakdown

Voltage

30V

23V

30V

Average Current Rating

0.5A

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