LT3754 데이터 시트보기 (PDF) - Linear Technology

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LT3754

16-Channel × 50mA LED Driver

Linear Technology 

LT3754

Applications Information

Two external resistors program the maximum IC junction

temperature using a resistor divider from the VREF pin,

as shown in Figure 9. Choose the ratio of R1 and R2 for

the desired junction temperature. Figure 10 shows the

relationship of TSET voltage to junction temperature, and

Table 8 shows commonly used values for R1 and R2.

31

VREF

R2

LT3754

30

TSET

R1

3754 F09

Figure 9. Programming the TSET Pin

950

900

850

800

750

700

650

600

550

500

0

VPTAT

25 50 75 100 125 150

JUNCTION TEMPERATURE (°C)

3754 F10

Figure 10. Programing the TSET Pin Threshold

Table 7. Resistor Values to Program Maximum IC Junction

Temperature (VREF (Typical) = 1.485V)

TJ (°C)

R1 (k)

R2 (k)

TSET (V)

100

24.9

20

0.824

115

28.0

20

0.866

130

30.9

20

0.902

Programming Overvoltage Protection (OVP) level

The LT3754 LED driver provides optimum protection to

the LEDs and the external MOSFET by providing a pro-

grammable maximum regulated output voltage limit using

the OVPSET pin. The Overvoltage Protection (OVP) level

is programmed as:

OVP(maximum regulated VOUT) = 57 • OVPSET

If every LED string fails open or the multiple string LED

display becomes disconnected the LT3754 LED driver loop

regulates to the programmed OVP level. The OVP level

should be programmed to a level high enough to regulate

the LED strings but low enough to prevent damage to the

power switch and to minimize the voltage across the LED

pins upon reconnection of the LED strings. Recommended

OVP level is given by:

OVP(RECOMMENDED) = 1.2 • ((N • VF) + 1V)

where:

N = number of LEDs in each string,

VF = maximum LED forward voltage drop

and the scaling factor of 1.2 accounts for variation in the

generation of OVP from OVPSET pin voltage and start-up

logic requirements.

Example: For a converter operating with 10 LEDs per string

at a maximum forward voltage of 4V per LED, the OVP

level should be programmed to:

OVP(RECOMMENDED) = 1.2 • ((10 • 4) + 1V) = 49.2V

For

OVP

=

49.2V,

OVPSET

=

49.2

57

=

0.863V

The OVPSET pin voltage can be generated using a resistor

divider from the REF pin.

3754fc

20

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