LTC3738 Linear Technology, LTC3738 Datasheet - Page 29

• Manufacturer Part Number: LTC3738
• Description: 3-Phase Buck Controller
• Manufacturer: Linear Technology

w w w . D a t a S h e e t 4 U . c o m
APPLICATIO S I FOR ATIO
result that is within 10% to 20% of the final application.
The temperature of the MOSFET’s die temperature may
require interative calculations if one is not familiar typical
performance. A maximum operating junction tempera-
ture of 90° to 100°C for the MOSFETs is recommended
for high reliability applications.
Common output path DC loss:
This totals 3.375W + C
Total of all three main MOSFET’s DC loss:
This totals 1.3W + C
Total of all three synchronous MOSFET’s DC loss:
This totals 3.2W.
Total of all three main MOSFET’s AC loss:
P
MAIN
P
P
P
COMPATH
MAIN
SYNC
=
N
≈
=
⎛
⎜
⎝
⎛
⎜
⎝
3
V
N
V
(
OUT
5
⎛
⎜
⎝
≈
V
IN
V
1
IN
N
–
– .
⎛
⎜
⎝
)
⎞
⎟
⎠
2
1
I
V
1 8
⎛
⎜
⎝
MAX
V
U
OUT
( )( )
I
N
MAX
IN
45
2 3
INESR
N
V
OUTESR
A
⎞
⎟
⎠
⎞
⎟
⎠
+
2
⎞
⎟
⎠
⎛
⎜
⎝
U
(
(
2
1 8
I
loss.
R
2
MAX
(
.
Ω
1 δ
N
L
1
+
V
+
)(
loss.
⎞
⎟
⎠
⎞
⎟
⎠
R
140
2
(
)
SENSE
R
400
(
1
W
DS ON
pF
+
(
kHz
δ
)
)
)
+
)
R
)
+
DS ON
C
=
OUTESR
C
(
6 3
INESR
U
.
)
W
Loss
Loss
This totals 0.14W at V
0.875W at V
Total of all three synchronous MOSFET’s AC loss:
This totals 0.085W at V
0.213W at V
experience the Miller capacitance dissipation issue that
the main switch does because the bottom switch turns on
when its drain is close to ground.
The Schottky rectifier loss assuming 50ns nonoverlap
time:
This totals 1.26W.
The total output power is (1.3V)(45A) = 58.5W and the
total input power is approximately 67W so the % loss of
each component is as follows:
The numbers above represent the values at V
2 • 3(0.7V)(15A)(50ns)(400kHz)
Main switch AC loss (V
Main switch DC loss
Synchronous switch AC loss
Synchronous switch DC loss
Power path loss
( )
3
Q
G
V
DSSPEC
V
IN
IN
IN
= 20V.
= 20V. The bottom MOSFET does not
( ) ( )(
f
=
IN
IN
3 16
= 8V, 0.315W at V
= 8V, 0.128W at V
IN
= 12V)
nC
)
V
DSSPEC
V
IN
0.315W 0.47%
1.3W
0.128W 0.2%
3.2W
3.375W 5.05%
LTC3738
(
IN
400
IN
IN
= 12V and
= 12V and
kHz
= 12V.
1.9%
4.8%
29
)
3738f