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參數(shù)資料
| 型號： | SC2441AEVB |
| 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)： | 31/37頁 |
| 文件大?。?/td> | 1024K |
| 代理商： | SC2441AEVB |
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31
2006 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Applications Information
In Figure 21,
SC2441A
Q
is the gate charge needed to bring the gate-to-source
voltage V
to the threshold V
,
Q
is the additional gate charge required for the switch
current to reach its full-scale value I
.and
Q
is the charge needed to charge gate-to-drain (Miller)
capacitance when V
is falling.
Switching losses occur during the time interval [t
1
, t
3
].
Defining t
r
= t
3
-t
1
. t
r
can be approximated as
Q
(
t
cc
where R
is the total resistance from the driver supply
rail to the gate of the MOSFET. It includes the gate driver
internal impedance R
, external resistance R
ge
and the
gate resistance R
g
within the MOSFET i.e.
.
V
V
R
)
Q
gsp
gt
gd
2
gs
r
R
gt
= R
gi
+R
ge
+R
g
.
V
is the Miller plateau voltage shown in Figure 21.
Similarly
an approximate expression for t
f
is
.
gsp
gt
gd
gs2
f
V
)R
Q
(Q
t
Only a portion of the total losses P
= Q
V
f
is dissipated
in the MOSFET package. Here
Q
is the total gate charge
specified in the datasheet. The power dissipated within
the MOSFET package is
.
f
V
Q
R
R
P
s
cc
g
gt
g
tg
The total power loss of the top switch is then
P
t
= P
tc
+P
ts
+P
tg
.
If the input supply of the power converter varies over a
wide range, then it will be necessary to weigh the relative
importance of conduction and switching losses. This is
because conduction loss is inversely proportional to the
input voltage. Switching loss however increases with the
input voltage. The total power loss of MOSFET should be
calculated and compared for high-line and low-line cases.
The worst case is then used for thermal design.
Bottom Switch:
The RMS current in bottom switch can be calculated
.
1
)(
D
1
I
I
12
o
rms
,
Q
2
The conduction loss is then
P
bc
=I
Q2,rms
2
R
ds(on)
,
where R
is the channel resistance of bottom MOSFET.
If the input voltage to output voltage ratio is high (e.g.
V
=12V, V
=1.5V), the duty ratio D will be small. Since
the bottom switch conducts with duty ratio (1-D), the
corresponding conduction losses can be quite high.
Due to non-overlapping conduction between the top and
the bottom MOSFET’s, the internal body diode or the
external Schottky diode across the drain and source
terminals always conducts prior to the turn on of the
bottom MOSFET. The bottom MOSFET switches on with
only a diode voltage between its drain and source
terminals. The switching loss
s
d
o
2
f
r
2
1
bs
f
V
I
1
)(
t
t
P
is negligible due to near zero-voltage switching.
The gate loss is estimated as
.
f
V
Q
R
R
P
s
cc
g
gt
g
bg
The total bottom switch loss is then
P
b
=P
bc
+P
bs
+P
bg
.
Once the power losses P
for the top (P
) and bottom
(P
) MOSFET’s are known, thermal and package design
at component and system level should be done to verify
that the maximum die junction temperature (T
, usually
125
o
C) is not exceeded under the worst-case conditions.
The equivalent thermal impedance from junction to
ambient (
θ
ja
) should satisfy
T
max
,
ja
.
P
T
loss
max
,
θ
depends on the die to substrate bonding, packaging
material, the thermal contact surface, thermal compound
property, the available effective heat sink area and the
air flow condition (free or forced convection). Actual
temperature measurement of the prototype should be
carried out to verify the thermal design.
Integrated Power MOSFET Drivers
There are four internal MOSFET drivers in a dual-
channel step-down converter.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| SC2441ATETRT | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| 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 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SC2441ATETRT | 制造商:Semtech Corporation 功能描述: |
| 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 |
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