Application Information

CAPACITOR SELECTION

To minimize output and input voltage ripple, low equivalent

series resistance (ESR) ceramic capacitors are the best

choice to use for the input and output filters. For most display

applications, a 4.7µF capacitor is recommended for C

1µF for C

Larger output capacitors can be used to reduce ripple volt-

age. To guarantee good performance, a minimum of 0.47µF

C

must be taken to account for the true capacitance of a

multilayer ceramic capacitor. Smaller case size capacitors

typically have less capacitance for a given bias voltage as

compared to a larger case size capacitor with the same bias

voltage. Please confirm with capacitor manufacturer data

before selecting the capacitor.

Some recommended capacitor manufacturers include but

are not limited to:

Manufacturer

Description

Case Size

AVX

06033D105MAT-25V

0603

06036D475MAT-6.3V

0603

TDK

C2012X5R1A475M-10V

0805

Taiyo Yuden

TMK212BJ105KG-J

0805

EM212BJ475MG-16V

0805

muRata

GRM40-034B105K25

0805

GRM39X5R475K6.3

0603

INDUCTOR SELECTION

In order to maintain sufficient inductance, the saturation

current rating of the inductor used with the LM3519 should

be higher than the peak inductor current in the target appli-

cation. Inductors with low DCR values have less power loss

and higher efficiency. Larger inductor values such as 2.2µH

and 3.3µH can be used to optimize efficiency, frequency and

peak current. If 1µH is used, the peak inductor current,

frequency will be higher and the efficiency will be lower. Note

that the switching frequency ranges will be higher at lower

inductance. Typical frequency range is between 4 to 8MHz

for 1µH, 2 to 5MHz for 2.2µH and 2 to 4MHz for 3.3µH over

the input range. Below is a sample list of low profile induc-

tors.

Some recommended inductor manufacturers include but

are not limited to:

Manufacturer

L

Case Size

I

SAT

CoilCraft:

DO3314-102

1µH

3.3x3.3x1.4mm

2.1A

DO3314-222

2.2µH

1.6A

DO3314-332

3.3µH

1.4A

Coilcraft:

LPO3310-102ML

1µH

3.3x3.3x1.0 mm

1.6A

LPO3310-222ML

2.2µH

1.1A

LPO3310-332ML

3.3µH

0.95A

Cooper:

SD31121R0

1µH

3.1x3.1x1.4 mm

2.07A

SD3114-2R2

2.2µH

1.48A

SD3114-3R3

3.3uH

1.15A

Taiyo Yuden:

NR3015T1R0N

1µH

3.0x3.0x1.5 mm

2.1A

NR3015T2R2M

2.2µH

1.48A

NR3015T3R3M

3.3µH

1.21A

DIODE SELECTION

Diodes with low forward voltage ratings (V

capacitance magnitudes (C

high efficiency. The chosen diode must have a reverse

breakdown voltage rating (V

than the output voltage. The following criteria should be

followed when choosing a diode:

1.

V

put Voltage)

2.

I

≥ I

LOAD

(Load Current)

3.

I

≥

I

Some recommended diode manufacturers include but are

not limited to:

Maufacturer

Description

Vishay

SS12(1A/20V)

SS14(1A/40V)

SS16(1A/60V)

Central Semiconductor

CMSH1- 40M(1A/40V)

ONSemi

MBRS1540T3(1.5A/40V)

PWM DIMMING

The LED current is set internally by the LM3519 to 20mA

(typical); dimming control may be realized by applying a

pulse width modulated(PWM) signal to the En pin. For ex-

ample, a 50% duty cycle waveform will produce an average

current of 10mA. A control signal frequency between 17kHz

and 30kHz is suitable for dimming.

Although the LM3519 is capable of operation outside this

frequency range, it is not recommended to operate below

17kHz for the following reasons: 1) frequency below 100Hz

is likely to cause visible flicker in the light emitted by the LED

string. 2) frequency below 17kHz may induce audible noise

due to combinations of some capacitance/PCB. A PWM

frequency above 30kHz is possible but the current linearity

vs duty cycle will be affected.

If it is not possible to operate the dimming control above

17kHz, audible noise emission may be minimized by using

capacitors with low susceptibility to piezoelectric induced

stresses, such as poly film designs. Minimum audible noise

is most likely to occur when the PWM frequency is less than

2kHz. It is recommended that any application using a PWM

control signal below 17kHz be thoroughly evaluated for un-

desirable audible or visible noise.

DRIVING 2 LEDs

The LM3519 is optimized to drive up to 4LEDs. When driving

2LEDs, a minimum inductance of 2.2µH is required to main-

tain good loop regulation and current accuracy. If a smaller

inductor is used, the LED current will have more variation

with input voltage than a typical application. The following

curve illustrates the behavior.

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