參數(shù)資料
型號: LTC3731H
廠商: Linear Technology Corporation
英文描述: 3-Phase, 600kHz, Synchronous Buck Switching Regulator Controller
中文描述: 3相,600kHz的,同步降壓開關穩(wěn)壓器控制器
文件頁數(shù): 27/32頁
文件大小: 323K
代理商: LTC3731H
27
LTC3731H
3731hf
Total of all three main MOSFET’s DC loss:
P
N
V
V
I
N
R
MAIN
OUT
IN
MAX
DS ON
(
=
+
(
)
2
1
δ
)
+
C
Loss
INESR
This totals 0.87W + C
INESR
loss (at 90
°
C).
Total of all three synchronous MOSFET’s DC loss:
P
N
V
V
I
N
R
SYNC
OUT
IN
MAX
DS
=
+
(
)
1
1
2
(
ON)
δ
This totals 7.2W at 90
°
C.
Total of all three main MOSFET’s AC loss:
P
V
A
pF
V
V
V
kHz
W
MAIN
IN
+
=
3
45
2 3
2
1000
)(
1
–1 8
5
1
1 8
.
400
6 3
.
2
(
)
( )( )(
)
(
)
This totals 1W at V
IN
= 8V, 2.25W at V
IN
= 12V and 6.25W
at V
IN
= 20V.
Total of all three synchronous MOSFET’s AC gate loss:
( )
3
( )
f
6 15
)
(
)
4 5
E
Q
V
V
nC
V
V
G
IN
DSSPEC
IN
DSSPEC
=
APPLICATIOU
W
U
U
This totals 0.08W at V
IN
= 8V, 0.12W at V
IN
= 12V and
0.19W at V
IN
= 20V. The bottom MOSFET does not
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:
2 3(0.7V)(15A)(50ns)(4E5)
This totals 1.26W.
The total output power is (1.3V)(45A) = 58.5W and the
total input power is approximately 60W so the % loss of
each component is as follows:
Main switch’s AC loss (V
IN
= 12V) 2.25W
Main switch’s DC loss
Synchronous switch AC loss
Synchronous switch DC loss
Power path loss
The numbers above represent the values at V
IN
= 12V. It
can be seen from this simple example that two things can
be done to improve efficiency: 1) Use two MOSFETs on the
synchronous side and 2) use a smaller MOSFET for the
main switch with smaller C
MILLER
to better balance the AC
loss with the DC loss. A smaller, less expensive MOSFET
can actually perform better in the task of the main switch.
3.75%
1.5%
0.3%
12%
6.1%
0.87W
0.19W
7.2W
3.7W
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