LT3743IUFD#PBF Linear Technology, LT3743IUFD#PBF Datasheet - Page 13

• Manufacturer Part Number: LT3743IUFD#PBF
• Description: IC LED DRVR HP CONST CURR 28QFN
• Manufacturer: Linear Technology
• Type: High Power, Constant Currentr

Specifications of LT3743IUFD#PBF

• Topology: High Side, Low Side, PWM, Step-Down (Buck)
• Number Of Outputs: 1
• Internal Driver: No
• Type - Primary: General Purpose
• Type - Secondary: RGB
• Frequency: 200kHz ~ 1MHz
• Voltage - Supply: 6 V ~ 36 V
• Mounting Type: Surface Mount
• Package / Case: 28-QFN
• Operating Temperature: -40°C ~ 125°C
• Internal Switch(s): Yes
• Efficiency: 92%
• Led Driver Application: Lighting
• No. Of Outputs: 1
• Output Current: 20A
• Output Voltage: 40V
• Input Voltage: 6V To 36V
• Dimming Control Type: PWM
• Operating Temperature Range: -40°C To +125°C
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Current - Output / Channel: -

APPLICATIONS INFORMATION
Programming Inductor Current
The analog voltage at the CTRL_L and CTRL_H pins is
buffered and produces a reference voltage, V
an internal resistor. The regulated average inductor current
is determined by:
where R
age inductor current, which is equal to the LED current.
Figure 2 shows the LED current vs R
power dissipation in the resistor will be:
Table 1 contains several resistors values, the correspond-
ing maximum current and power dissipation in the sense
resistor. Figure 3 shows the power dissipation in R
Table 1. Sense Resistor Values
MAXIMUM LED
CURRENT (A)
I
P
O
RS
=
10
25
=
1
5
30 •
V
S
(
Figure 2. R
CTRL
is the external sense resistor and I
0 05
30
25
20
15
10
.
R
5
0
R
0
S
S
V
2
)
RESISTOR, R
2
4
S
Value Selection for LED Current
6
50
10
5
2
8
R
S
10
(mΩ)
S
(mΩ)
12
14
POWER DISSIPATION (W)
16
S
18
3743 F02
. The maximum
20
0.05
0.25
1.25
O
CTRL
0.5
is the aver-
, across
S
.
Inductor Selection
The recovery time between regulated states is critical
to maintaining accurate control of the LED current. For
this reason, sizing the inductor to have no less than 30%
peak-to-peak ripple will provide excellent recovery time
with reasonable ripple. The overcurrent set point is equal
to the high level regulated current level set by the CTRL_H
pin with an additional 23mV offset between the SENSE
and SENSE
should be at least 20% higher than the maximum regu-
lated current. The following equation sizes the inductor
to achieve a reasonable recovery time while minimizing
the inductor ripple:
where V
regulated current in the inductor and f
frequency. Using this equation, the inductor will have ap-
proximately 10% ripple at maximum regulated current.
Table 2. Recommended Inductor Manufacturers
L =
Würth Electronics
F
V
0.2 • f
is the LED forward voltage drop, I
IN
NEC-Tokin
VENDOR
Coilcraft
1.4
1.2
1.0
0.8
0.6
0.4
Sumida
0.2
–
Vishay
• V
0
( )
pins. The saturation current for the inductor
0
Figure 3. Power Dissipation in R
S
F
•I
2
– V
O
4
( )
• V
F
6
IN
2
8
R
S
10
(mΩ)
12
14
www.we-online.com
www.nec-tokin.com
www.coilcraft.com
www.sumida.com
www.vishay.com
16
S
WEBSITE
18 20
3743 F03
O
is the switching
is the maximum
S
LT3743
13
3743fb
+