LT3491EDC#PBF Linear Technology, LT3491EDC#PBF Datasheet - Page 8

• Manufacturer Part Number: LT3491EDC#PBF
• Description: IC, LED DRVR, DFN6
• Manufacturer: Linear Technology

Specifications of LT3491EDC#PBF

• Led Driver Application: Mobile Phone Display Lighting, General LED Lighting
• No. Of Outputs: 1
• Output Current: 200mA
• Output Voltage: 32V
• Input Voltage: 2.5V To 12V
• Dimming Control Type: PWM
• Topology: Boost (Step Up)
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
LT3491
For low DCR inductors, which is usually the case for this
application, the peak inrush current can be simplified as
follows:
where L is the inductance, r is the DCR of the inductor and
C is the output capacitance.
Table 3 gives inrush peak currents for some component
selections.
Table 3. Inrush Peak Currents
PROGRAMMING LED CURRENT
The feedback resistor (R
(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 accurate
LED current, precision resistors are preferred (1% is
recommended). The formula and table for R
tion are shown below.
8
CAP
I
R
α
ω
V
PK
IN
SENSE
4.2
4.2
4.2
4.2
=
=
(V)
– V
=
2
V
r
•
L C
LED
IN
L
L
=
1
•
•
– .
) control the LED current.
200
ω
0 6
–
r (Ω)
0.58
I
0.3
1.2
1.6
LED
4 •
mV
r r
• exp –
U
2
L
2
⎛
⎝ ⎜
U
L (µH)
SENSE
10
10
15
15
ω
α
•
) and the sense voltage
π
2
⎞
⎠ ⎟
W
C
OUT
1.0
1.0
1.0
1.0
(µF)
SENSE
U
I
1.06
0.86
0.83
0.68
P
selec-
(A)
Table 4. R
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 filtered PWM signal or directly with a
PWM signal.
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 dimming
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
As the CTRL pin voltage increases beyond 1.5V, it has no
effect on the LED current.
The LED current can be set by:
Feedback voltage variation versus control voltage is given
in the Typical Performance Characteristics.
I
I
LED
LED
≈
≈
SENSE
R
200
6
I
.2 2 5
SENSE
LED
10
15
20
mV
V
Value Selection for 200mV Sense
5
(mA)
CTRL
•
R
,
SENSE
when V
,
when V
CTRL
>
CTRL
1 5
.
R
V
SENSE
<
13.3
40
20
10
1 25
.
(Ω)
V
LED
3491fa
.