LTC3830-1 Linear Technology, LTC3830-1 Datasheet - Page 14

• Manufacturer Part Number: LTC3830-1
• Description: High Power Step-Down Synchronous DC/DC Controllers for Low Voltage Operation
• Manufacturer: Linear Technology

LTC3830/LTC3830-1
APPLICATIO S I FOR ATIO
P
efficiency or allowable thermal dissipation. A typical high
efficiency circuit designed for 5V input and 3.3V at 10A
output might allow no more than 3% efficiency loss at full
load for each MOSFET. Assuming roughly 90% efficiency
at this current level, this gives a P
and a required R
Note that the required R
of Q1 in this example. This application might specify a
single 0.03 device for Q2 and parallel two more of the
same devices to form Q1. Note also that while the required
R
pation numbers are only 1.1W per device or less; large
TO-220 packages and heat sinks are not necessarily
required in high efficiency applications. Siliconix Si4410DY
Table 1. Recommended MOSFETs for LTC3830 Applications
PARTS
Siliconix SUD50N03-10
TO-252
Siliconix Si4410DY
SO-8
ON Semiconductor MTD20N03HDL
DPAK
Fairchild FDS6670A
S0-8
Fairchild FDS6680
SO-8
ON Semiconductor MTB75N03HDL
DD PAK
IR IRL3103S
DD PAK
IR IRLZ44
TO-220
Fuji 2SK1388
TO-220
Note: Please refer to the manufacturer’s data sheet for testing conditions and detailed information.
14
MAX
DS(ON)
(3.3V)(10A/0.9)(0.03) = 1.1W per FET
R
R
DS ON Q
DS ON Q
should be calculated based primarily on required
(
(
values suggest large MOSFETs, the power dissi-
)
)
1
2
( .
(
(
DS(ON)
3 3
5
5
V
V
(
U
) • ( .
V
5
– .
V
)(
3 3
) • ( .
1 1
10
DS(ON)
of:
U
V
A
W
1 1
)(
)
2
)
10
W
for Q2 is roughly twice that
)
A
AT 25 C (m )
0 017
)
MAX
.
2
R
W
DS(ON)
19
20
35
10
19
28
37
8
9
value of:
0 032
.
U
RATED CURRENT (A)
11.5 at 25 C
10 at 100 C
16 at 100 C
59 at 100 C
45 at 100 C
36 at 100 C
15 at 25 C
10 at 25 C
20 at 25 C
13 at 25 C
75 at 25 C
64 at 25 C
50 at 25 C
35 at 25 C
8 at 70 C
or International Rectifier IRF7413 (both in SO-8) or Siliconix
SUD50N03-10 (TO-252) or ON Semiconductor
MTD20N03HDL (DPAK) are small footprint surface mount
devices with R
work well in LTC3830 circuits. Using a higher P
in the R
cost and the circuit efficiency and increases the MOSFET
heat sink requirements.
Table 1 highlights a variety of power MOSFETs for use in
LTC3830 applications.
Inductor Selection
The inductor is often the largest component in an LTC3830
design and must be chosen carefully. Choose the inductor
value and type based on output slew rate requirements. The
maximum rate of rise of inductor current is set by the
inductor’s value, the input-to-output voltage differential and
the LTC3830’s maximum duty cycle. In a typical 5V input,
3.3V output application, the maximum rise time will be:
DC
MAX
DS(ON)
• (
TYPICAL INPUT
CAPACITANCE
L
V
calculations generally decreases the MOSFET
O
DS(ON)
C
IN
ISS
3200
2700
3200
2070
4025
1600
3300
1750
880
–
(pF)
V
OUT
values below 0.03 at 5V of V
)
. 1 615
L
O
JC
1.67
2.08
1.8
1.4
( C/W)
25
25
1
1
A
s
T
JMAX
MAX
sn3830 3830fs
175
150
150
150
150
150
175
175
150
GS
( C)
value
that