Datasheet

LT3743
15
3743fd
Whenever possible, utilize a switching MOSFET that
minimizes the total gate charge to limit the internal power
dissipation of the LT3743.
Table 3. Recommended Switching FETs
V
IN
(V)
V
OUT
(V)
I
D
(A) TOP FET BOTTOM FET MANUFACTURER
8 4 5-10 RJK0365DPA RJK0330DPB Renesas
www.renesas.com
24 4 5 RJK0368DPA RJK0332DPB
24 2-4 20 RJK0365DPA RJK0346DPA
12 2-4 10 FDMS8680 FDMS8672AS Fairchild
www.fairchildsemi.
com
36 4 20 Si7884BDP SiR470DP Vishay
www.vishay.com
24 4 40 PSMN4R0-
30YL
RJK0346DPA NXP/Philips
www.nxp.com
Input Capacitor Selection
The input capacitor should be
sized at 4µF for every 1A
of output current and placed very close to the high side
MOSFET. A small 1µF ceramic capacitor should be placed
near the V
IN
and ground pins of the LT3743 for optimal
noise immunity. The input capacitor should have a ripple
current rating equal to half of the maximum output current.
It is recommended that several low ESR ceramic capacitors
be
used as the input capacitance. Use only type X5R or
X7R capacitors as they maintain their capacitance over a
wide range of operating voltages and temperatures.
Output Capacitor Selection
The output capacitors need to have very low ESR (equivalent
series resistance) to allow the LED current to ramp quickly.
A minimum of 50µF/A of load current should be used in
most designs. The capacitors also
need to be surge rated
to the maximum output current. To achieve the lowest
possible ESR, several low ESR capacitors should be used
in parallel. Many applications benefit from the use of high
density POSCAP capacitors, which are easily destroyed
when exposed to overvoltage conditions. To prevent this,
select POSCAP capacitors that have a voltage rating that
is at least 50% higher than the regulated voltage
C
BOOT
Capacitor Selection
The C
BOOT
capacitor must be sized less than 220nF and
more than 50nF to ensure proper operation of the LT3743.
Use 220nF for high current switching MOSFETs with high
gate charge.
APPLICATIONS INFORMATION
Figure 4a. Power Loss Example for M1 Figure 4b. Power Loss Example for M2
Figure 4
INPUT VOLTAGE (V)
0
4
5
7
30
3743 F04a
3
2
10 20 40
1
0
6
MOSFET POWER LOSS (W)
TOTAL
OHMIC
TRANSITIONAL
INPUT VOLTAGE (V)
0
MOSFET POWER LOSS (W)
1.0
1.5
40
3743 F04b
0.5
0
10
20
30
2.5
2.0
TOTAL
OHMIC
TRANSITIONAL