LT3741IFE-PBF View Datasheet(PDF) - Linear Technology
Part Name
Description
Manufacturer
LT3741IFE-PBF Datasheet PDF : 24 Pages
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LT3741
Applications Information
7
6
5
TOTAL
4
TRANSITIONAL
3
2
1
OHMIC
0
0
10
20
30
40
INPUT VOLTAGE (V)
3741 F04a
Figure 4a. Power Loss Example for M1
Figure 4
2.5
2.0
1.5
TOTAL
1.0
TRANSITIONAL
0.5
OHMIC
0
0
10
20
30
40
INPUT VOLTAGE (V)
3741 F04b
Figure 4b. Power Loss Example for M2
Table 3. Recommended Switching FETs
VIN VOUT IOUT
(V) (V) (A)
TOP FET
BOTTOM FET MANUFACTURER
8 4 5-10 RJK0365DPA RJK0330DPB Renesas
24 4 5 RJK0368DPA RJK0332DPB www.renesas.com
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- RJK0346DPA NXP/Philips
30YL
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 VIN and ground pins of the LT3741 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 reduce output ripple. A minimum of
20µF/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 ap-
plications 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
CBOOT Capacitor Selection
The CBOOT capacitor must be sized less than 220nF and
more than 50nF to ensure proper operation of the LT3741.
Use 220nF for high current switching MOSFETs with high
gate charge.
VCC_INT Capacitor Selection
The bypass capacitor for the VCC_INT pin should be larger
than 5µF for stability and has no ESR requirement. It
is recommended that the ESR be lower than 50mΩ to
reduce noise within the LT3741. For driving MOSFETs
with gate charges larger than 10nC, use 0.5µF/nC of total
gate charge.
Soft-Start
Unlike conventional voltage regulators, the LT3741 utilizes
the soft-start function to control the regulated inductor cur-
rent. The charging current is 11µA and reduces the regulated
current when the SS pin voltage is lower than CTRL1.
3741f
15
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