LT3590ESC8#PBF Linear Technology, LT3590ESC8#PBF Datasheet - Page 9

• Manufacturer Part Number: LT3590ESC8#PBF
• Manufacturer: Linear Technology

Specifications of LT3590ESC8#PBF

• Operating Supply Voltage (typ): 5/9/12/15/18/24V
• Number Of Segments: 10
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Package Type: SC-70
• Pin Count: 8
• Mounting: Surface Mount
• Operating Supply Voltage (min): 4.5V
• Lead Free Status / RoHS Status: Compliant

Programming LED Current
The feedback resistor (R1 in Figure 1) and the sense volt-
age (V
The CTRL pin controls the sense reference voltage as
shown in the Typical Performance Characteristics. For
CTRL higher than 1.5V, the sense reference is 200mV,
which results in full LED current. In order to have accu-
rate LED current, precision resistors are preferred (1%
is recommended). The formula and table for R1 selection
are shown below.
Table 3. R1 Theoretical Value for 200mV Sense
Dimming Control
There are three different types of dimming control circuits.
The LED current can be set by modulating the CTRL pin
with a DC voltage, a fi ltered PWM signal or directly with
a PWM signal.
APPLICATIONS INFORMATION
I
R
LED
1
=
IN
Figure 4. Dimming and Shutdown Using CTRL Pin
=
200
- V
I
V
I
LED
LED
LED
0.25
0.20
0.15
0.10
0.05
IN
mV
10
20
30
40
50
0
(mA)
−
0
) control the LED current.
R
1
V
LED
0.5
V
CTRL
1.0
(V)
1.5
R1 (Ω)
6.8
5.0
4.0
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20
10
2.0
Using a DC Voltage
For some applications, the preferred method of brightness
control is a variable DC voltage to adjust the LED current.
The CTRL pin voltage can be modulated to set the dim-
ming of the LED string. As the voltage on the CTRL pin
increases from 0V to 1.5V, the LED current increases from
0 to I
it has no effect on the LED current.
The LED current can be set by:
Feedback voltage variation versus control voltage is
shown in Figure 4.
Using a Filtered PWM Signal
A variable duty cycle PWM can be used to control the
brightness of the LED string. The PWM signal is fi ltered
(Figure 5) by a RC network and fed to the CTRL pin.
The corner frequency of R1, C1 should be much lower
than the frequency of the PWM signal. R1 needs to be
much smaller than the internal impedance in the CTRL
pin which is 100kΩ.
I
I
LED
LED
Figure 5. Dimming Control Using a Filtered PWM Signal
LED
=
=
. As the CTRL pin voltage increases beyond 1.5V,
kHz TYP
200mV
6.25 • R1
PWM
V
R1
CTRL
10k
R1
,when V
,when V
C1
1μF
CTRL
CTRL
CTRL
> 1.5V
LT3590
< 1.25V
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LT3590
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