Datasheet

LT3597
12
3597fa
applicaTions inForMaTion
Undervoltage Lockout (UVLO)
The EN/UVLO can be used to program the input UVLO
threshold by connecting it to a resistor divider from the
V
IN
pin as shown in Figure 2.
Programming Maximum LED Current
Maximum LED current can be programmed by placing a
resistor (R
ISET1-3
) between the ISET1-3 pin and ground.
R
ISET1-3
values between 20k and 100k can be chosen to
set the maximum LED current between 100mA and 20mA
respectively.
The LED current is programmed according to the follow-
ing equation:
I
LED1-3
= 2 •
1V
R
ISET1-3
(mA)
See Table 5 and Figure 3 for resistor values and corre-
sponding programmed LED current.
Table 5. LED Current Programming
R
ISET1-3
VALUE (kΩ) LED CURRENT (mA)
20 100
25 80
33.3 60
50 40
100 20
Figure 3. R
ISET1-3
Value for LED Current
R
SET1-3
(kΩ)
0
LED CURRENT (mA)
100
80
40
60
20
0
25 75
3597 F03
10050
Figure 2. EN/UVLO Control
LT3597
3597 F02
+
–
1.51V
EN/UVLO
R2
R1
V
IN
Select R1 and R2 according to the following equation:
V
IN(UVLO)
= 1.51V • 1+
R2
R1






In UVLO an internal 5.1µA pull-down current source is con-
nected to the pin for programmable UVLO hysteresis. The
hysteresis can be set according to the following equation:
V
UVLO(HYST)
= 5.1µA • R2
Care must be taken if too much hysteresis is programmed,
the pin voltage might drop too far and cause the current
source to saturate.
Once the EN/UVLO pin falls below 0.4V, the part enters
into shutdown.