LT3596IUHG Просмотр технического описания (PDF) - Linear Technology
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LT3596IUHG Datasheet PDF : 22 Pages
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LT3596
Applications Information
VIN
LT3596
R2
EN/UVLO
R1
1.51V
3596 F02
Figure 2. EN/UVLO Control
In UVLO an internal 5.1µA (typical) pull-down current
source is connected to the pin for programmable UVLO
hysteresis. The hysteresis is set according to the follow-
ing equation:
VUVLO(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 goes below 0.4V, the part enters
shutdown.
Programming Maximum LED Current
Maximum LED current is programmed by placing a resistor
(RISETn) between the ISETn pin and ground. RISETn 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:
ILED1-3
=
1V
•
2000
RISETn
where RISETn is in kΩ and ILEDn is in mA. See Table 5 and
Figure 3 for resistor values and corresponding programmed
LED current.
Table 5. RISETn Value for LED Current
RISETn VALUE (kΩ)
20
24.9
33.2
49.9
100
LED CURRENT (mA)
100
80
60
40
20
12
LED Current Dimming
The LT3596 has two different types of dimming control.
The LED current is dimmed using the CTRLn pin or the
PWMn pin.
For some applications, a variable DC voltage that adjusts
the LED current is the preferred method for brightness
control. In this case, the CTRLn pin is modulated to set
the LED dimming. As the CTRLn pin voltage rises from
0V to 1V, the LED current increases from 0mA to the
maximum programmed LED current in a linear fashion
(see Figure 4). As the CTRLn pin increases beyond 1V,
the maximum programmed LED current is maintained.
If this type of dimming control is not desired, the CTRLn
pin can be connected to VREF .
100
80
60
40
20
0
0
25
50
75
100
RISETn (kΩ)
3596 F03
Figure 3. RISETn Value for LED Current
100
RISETn = 20k
75
50
25
0
0 0.25 0.5 0.75 1 1.25 1.5
CTRLn VOLTAGE (V)
3596 F04
Figure 4. LED Current vs CTRLn Voltage
3596fa
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