LTC3831 LINER [Linear Technology], LTC3831 Datasheet - Page 14

• Manufacturer Part Number: LTC3831
• Description: High Power Synchronous Switching Regulator Controller for DDR Memory Termination
• Manufacturer: LINER [Linear Technology]

LTC3831
APPLICATIO S I FOR ATIO
efficiency circuit designed for 2.5V input and 1.25V at 5A
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 while the required R
MOSFETs, the power dissipation numbers are only 0.21W
per device or less; large TO-220 packages and heat sinks
are not necessarily required in high efficiency applications.
Siliconix Si4410DY or International Rectifier IRF7413 (both
in SO-8) or Siliconix SUD50N03-10 (TO-252) or ON Semi-
conductor MTD20N03HDL (DPAK) are small footprint
surface mount devices with R
5V of V
higher P
Table 1. Recommended MOSFETs for LTC3831 Applications
PARTS
Siliconix SUD50N03-10
TO-252
Siliconix Si4410DY
SO-8
ON Semiconductor MTD20N03HDL
D PAK
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
(1.25V)(5A/0.9)(0.03) = 0.21W per FET
R
R
DS ON Q
DS ON Q
(
(
GS
MAX
)
)
that work well in LTC3831 circuits. Using a
1
2
value in the R
( .
( .
DS(ON)
2 5
2 5
( .
1 25
( .
2 5
U
V
V
) • ( .
– .
V
V
of:
) • ( .
)(
1 25
0 21
U
5
A
0 21
DS(ON)
DS(ON)
)
V
W
DS(ON)
2
)(
)
W
AT 25 C (m )
5
A
MAX
)
calculations generally
R
W
values below 0.03 at
0 017
)
DS(ON)
2
values suggest large
.
19
20
35
10
19
28
37
8
9
value of:
0 017
.
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
decreases the MOSFET cost and the circuit efficiency and
increases the MOSFET heat sink requirements.
Table 1 highlights a variety of power MOSFETs that are for
use in LTC3831 applications.
Inductor Selection
The inductor is often the largest component in an LTC3831
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 LTC3831’s maximum duty cycle. In a typical 2.5V input
1.25V output application, the maximum rise time will be:
where L
quency compensation, the combination of the inductor
and output capacitor values determine the transient recov-
ery time. In general, a smaller value inductor improves
transient response at the expense of ripple and inductor
core saturation rating. A 2 H inductor has a 0.57A/ s rise
DC
MAX
O
is the inductor value in H. With proper fre-
• (
TYPICAL INPUT
CAPACITANCE
L
V
O
C
IN
ISS
3200
2700
3200
2070
4025
1600
3300
1750
880
–
(pF)
V
OUT
)
. 1 138
L
O
JC
1.67
2.08
1.8
1.4
( C/W)
25
25
1
1
A
s
T
JMAX
175
150
150
150
150
150
175
175
150
( C)
3831f