LT3754 datasheet(20/28 Pages) LINER

20 / 28 page

LT3754

3754f

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.

Programming Overvoltage Protection (OVP) level

The LT3754 LED driver provides optimum protection

to the LEDs and the external MOSFET by providing a

programmable 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 startup

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

For

()

. • (

• )

()=

1 2

10 4

49 2

0 863

VOVP

SET

The OVPSET pin voltage can be generated using a resistor

divider from the REF pin.

Figure 9. Programming the TSET Pin

Figure 10. Programing the TSET Pin Threshold

3754 F09

LT3754

VREF

TSET

JUNCTION TEMPERATURE (°C)

500

600

700

800

100

125

150

950

550

650

750

850

900

3598 F10

VPTAT

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

0.824

115

28.0

0.866

130

30.9

0.902

LT3754 Datasheet(PDF) 20 Page - Linear Technology

LT3754 Datasheet(HTML) 20 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL