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LT3599FE

4-String 120mA LED Driver with ±1.5% Current Matching

Linear Technology 

LT3599

Operation

SHORTLED and OPENLED detection are disabled during

the start-up phase to avoid false flag generation. If an LED

string is open during normal operation, it will no longer

be used to regulate the output voltage. The output voltage

will regulate itself to find the LED string with the lowest

LED pin voltage. Fault detection (SHORTLED, OPENLED)

is updated when the PWM pin is high and latched when

the PWM pin is low.

During start-up, 11µA of current charges the external

soft-start capacitor. The SS pin directly limits the rate

of voltage rise on the VC pin, which in turn, limits the

peak switch current. Soft-start also enables switching

frequency foldback to provide a clean start-up for the

LT3599. Switch current limit protects the power switch

and external components.

Applications Information

Inductor Selection

Table 1 lists several inductors that work well with the

LT3599, however, there are many other manufacturers and

devices that can be used. Consult each manufacturer for

detailed information on their entire range of parts. Ferrite

core inductors should be used to obtain the best efficiency.

Choose an inductor that can handle the necessary peak

current without saturating. Also, ensure that the inductor

has a low DCR (copper wire resistance) to minimize I2R

power losses. Values between 4.7µH and 22µH will suffice

for most applications.

Inductor manufacturers specify the maximum current

rating as the current where inductance falls by a given

percentage of its nominal value. An inductor can pass a

current greater than its rated value without damaging it.

Consult each manufacturer to determine how the maximum

inductor current is measured and how much more current

the inductor can reliably conduct.

Table 1. Recommended Inductors

PART

L MAX DCR CURRENT

(µH) (Ω) RATING (A)

VENDOR

B1015AS-100M 10 0.07

817FY-4R7M

4.7 0.06

2.2 TOKO

2.26 www.toko.com

744065100

74454068

74454010

10 0.04

6.8 0.055

10 0.065

3

Würth Electronics

2.2 www.we-online.com

2

CDH115-100

10

CDH74NP-120L 12

CDH74NP-150L 15

0.028

0.065

0.083

3

Sumida

2.45 www.sumida.com

2.10

IHLP2020-BZ

IHLP2525-BD

10 0.184

10 0.116

2.3 Vishay

2.5 www.vishay.com

Capacitor Selection

Low ESR (equivalent series resistance) ceramic capaci-

tors should be used at the output to minimize the output

ripple voltage. Use only X5R or X7R dielectrics, as these

materials retain their capacitance over wider voltage and

temperature ranges than other dielectrics. A 4.7µF to 10µF

output capacitor is sufficient for most high output current

designs. Table 2 lists some suggested manufacturers.

Consult the manufacturers for detailed information on

their entire selection of ceramic parts.

Table 2. Recommended Ceramic Capacitor Manufacturers

Taiyo Yuden

(408) 573-4150

www.t-yuden.com

AVX

(843) 448-9411

www.avxcorp.com

Murata

(770) 436-1300

www.murata.com

Kemet

(408) 986-0424

www.kemet.com

Diode Selection

Schottky diodes, with their low forward voltage drop and

fast switching speed, should be used for all LT3599 ap-

plications. Table 3 lists several Schottky diodes that work

well. The diode’s average current rating must exceed the

application’s average output current. The diode’s maximum

reverse voltage must exceed the application’s output volt-

age. A 2A diode is sufficient for most designs. For PWM

dimming applications, be aware of the reverse leakage

current of the diode. Lower leakage current will drain the

output capacitor less, allowing for higher dimming range.

3599ff

10

For more information www.linear.com/LT3599

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