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參數(shù)資料
| 型號： | SC2441ATETRT |
| 廠商： | Semtech Corporation |
| 英文描述： | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| 中文描述： | 1.8V至20V的輸入2相同步降壓與升壓轉(zhuǎn)換器控制器 |
| 文件頁數(shù)： | 30/37頁 |
| 文件大?。?/td> | 1024K |
| 代理商： | SC2441ATETRT |
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30
2006 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Applications Information
SC2441A
The losses in power MOSFET’s consist of
a) conduction loss due to the channel resistance R
,
b) switching loss due to the switch rise time t
r
and fall
time t
and
c) the gate loss due to the gate resistance R
G
.
Top Switch:
The RMS value of the top switch current is
.
1
D
I
I
12
o
rms
,
Q
2
Its conduction loss is then
P
tc
= I
Q1,rms
2
R
ds(on)
.
R
ds(on)
varies with temperature and gate-source voltage.
Curves showing R
ds(on)
variations can be found in
manufacturers’ data sheet. From the Si7882DP
datasheet, R
ds(on)
is less than 4.5mOhm when V
gs
is greater
than 5V. However R
ds(on)
increases by nearly 40% as the
junction temperature increases from 25°C to 125°C.
The switching losses can be estimated using the simple
formula
.
f
V
I
2
1
)(
t
t
P
s
in
o
f
r
2
1
ts
where t
is the rise time and t
is the fall time of the
switching process. To clarify these, we sketch the typical
MOSFET switching characteristics under clamped
inductive mode in Figure 21.
Figure 21. MOSFET switching characteristics
If D
1
>0.5 and D
2
> 0.5, then
.
I
1
D
1
I
2
D
1
)
I
I
)(
1
D
D
(
I
2
2
o
2
1
o
2
2
o
1
o
2
1
Cin
Power MOSFET Selection and Gate Drive
Main considerations in selecting the MOSFET’s are power
dissipation, cost and packaging. Switching losses and
conduction losses of the MOSFET’s are directly related
to the total gate charge (C
) and channel on-resistance
(R
). In order to judge the performance of MOSFET’s,
the product of the total gate charge and on-resistance is
used as a figure of merit (FOM). Transistors with the same
FOM follow the same curve in Figure 20.
0
1
5
10
Rds
15
20
20
0
20
40
FOM:100*10^{-12}
FOM:200*10^{-12}
FOM:500*10^{-12}
On-resistance (mOhm)
G
50
1
Cg 100 Rds
(
)
Cg 200 Rds
(
)
Cg 500 Rds
(
)
Figure 20. Figure of merit curves.
The closer the curve is to the origin, the lower is the FOM.
This means lower switching loss or lower conduction loss
or both. It is difficult to find MOSFET’s with both low C
g
and low R
ds(on)
. Usually a trade-off between
R
ds(on)
and C
g
has to be made.
MOSFET selection also depends on applications. In many
applications, either switching loss or conduction loss
dominates for a particular MOSFET. For synchronous buck
converters with high input to output voltage ratios, the
top MOSFET is hard switched but conducts with very low
duty cycle. The bottom switch conducts at high duty cycle
but switches at near zero voltage. For such applications,
MOSFET’s with low C
g
are used for the top switch and
MOSFET’s with low R
ds(on)
are used for the bottom switch.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| SC2441 | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441EVB | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ITSTRT | Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2442 | High Performance Wide Input Range Dual Synchronous Buck Controller |
| SC2442H | High Performance Wide Input Range Dual Synchronous Buck Controller |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SC2441EVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Very Low Input Voltage 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ITSTRT | 制造商:Semtech Corporation 功能描述:Controller IC |
| SC2442 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Wide Input Range Dual Synchronous Buck Controller |
| SC2442H | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Wide Input Range Dual Synchronous Buck Controller |
| SC2442HITSTR | 制造商:Semtech Corporation 功能描述: |
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