Datasheet LT3595 (Analog Devices) - 10

LT3595
APPLICATIONS INFORMATION
LED string depends on the number of LEDs and can vary
Open LED Detection
from 0.47μF to 1μF. Refer to Table 2 for proper output The LT3595 detects an open LED on any channel and capacitor selection. reports it to the ⎯O⎯P⎯E⎯N⎯L⎯E⎯D pin. The fault also reports dur-
Table 2. Recommended Output Capacitor Values (VLED = 3.5V)
ing startup until the output voltage and LED current are
# LEDs COUT (μF)
in regulation. Therefore, it can also be used as a “power 3-10 0.47 ok” signal. 1-2 1
Programming LED Current Table 3. Recommended Ceramic Capacitor Manufacturers
The set resistor (RSET in the Block Diagram) controls Taiyo Yuden (408) 573-4150 the LED current in all sixteen channels. LED current as www.t-yuden.com a function of the RSET resistance is shown in the Typical TDK (847) 803-6100 Performance Characteristics. Common values for LED cur- www.component.tdk.com rent and their required resistor values are listed in Table 4. Murata (714) 852-2001 Since resistor error directly translates to LED current error, www.murata.com precision resistors are preferred (1% is recommended). Kemet (408)-986-0424 www.kemet.com The maximum allowed resistor value is 150k. Table 3 shows a list of several ceramic capacitor manufac-
Table 4. LED Current vs RSET Resistance
turers. Consult the manufacturers for detailed information
RSET (k
Ω
) ILED (mA)
on their entire selection of ceramic parts. 150 10 75.0 20 49.9 30 37.4 40 30.1 50 3595f 10