LT3599(RevD) Просмотр технического описания (PDF) - Linear Technology

Номер в каталоге

Компоненты Описание

производитель

LT3599
(Rev.:RevD)

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

Linear Technology 

LT3599

Applications Information

The companies below offer Schottky diodes with high

voltage and current ratings. Standard silicon diodes (PN

junction diodes) should not be used.

Table 3. Suggested Diodes

PART

MAX

CURRENT

(A)

MAX REVERSE

VOLTAGE

(V)

MANUFACTURER

B250A

2

DFLS240

2

B240A

2

B350A

3

B340A

3

50

Diodes, Inc.

40

www.diodes.com

40

50

40

HSM150G

1

HSM150J

1

HSM350G

3

50

Microsemi

50

www.microsemi.com

50

Overvoltage Protection

The LT3599 uses the FB pin to provide overvoltage protec-

tion. A resistor divider is connected between the VO_SW

pin and ground (Figure 2). There is an internal PMOS

switch between VOUT and VO_SW, which is controlled by

the PWM signal. The PMOS switch addition prevents the

feedback resistor divider from draining the output capaci-

tor during PWM off-period, allowing for a higher dimming

range without falsely tripping the OPENLED flag. It also

reduces the system current in shutdown. This PMOS has

about 1k resistance, so select FB resistor values taking

this resistance into account.

To set the maximum output voltage, select the values

of R1 and R2 (see Figure 2) according to the following

equation:

VOUT(M AX )

=

1.223V





1+

R2 

R1

LT3599

FB

VOUT

VO_SW

R2

R1

3599 F02

Figure 2. Overvoltage Protection Voltage Feedback Connections

The output voltage should be set 10% higher than the

normal LED string operating voltage. Under normal

operation, LED1 to LED4 pin voltages are monitored and

provide feedback information to the converter for output

voltage regulation given the programmed LED current.

The output voltage regulation loop is activated only when

all LEDs are open.

Programming Maximum LED Current

Maximum LED current can be programmed by placing a

resistor between the ISET pin and ground (RISET). The ISET

pin resistor can be selected from 11k to 44.2k.

The LED current can be programmed according to the

following equation:

ILED

≈ 1330

RISET

( Amps)

(CTRL > 1V)

See Table 4 and Figure 3 for resistor values and corre-

sponding programmed LED current.

LED current can also be adjusted by programming the

CTRL pin voltage.

Table 4. RISET Value Selection for LED Current

LED CURRENT (mA)

RESISTOR ON ISET PIN (k)

30mA

44.2

50mA

26.7

99mA

13.3

120mA

11

120

100

80

60

40

20

0

0 20 40 60 80 100 120 140 160

RISET (k)

3599 F03

Figure 3. RISET Value Selection for LED Current

3599fd

11

Share Link: