參數(shù)資料
型號(hào)： SC470ITSTRT
廠商： Semtech Corporation
英文描述： Synchronous Buck Controller for Dynamic Load-Voltage Applications
中文描述： 同步降壓控制器的動(dòng)態(tài)負(fù)載電壓應(yīng)用
文件頁數(shù)： 15/31頁
文件大?。?/td> 574K
代理商： SC470ITSTRT
15
2005 Semtech Corp.
www.semtech.com
SC470
POWER MANAGEMENT
Application Information (Cont.)
Figure 4: Dynamic Voltage Switching Using Direct
Drive Method (V
OUT(HIGH)
/V
OUT(LOW)
< 1.16 only)
Another option is to switch using an external discrete
MOSFET, as shown in Figure 5.
Figure 5: Dynamic Voltage Switching Using Indirect
Drive Method
The problem with the external MOSFET method is that
the drain-gate capacitance, c
, can cause the output
voltage to go even higher when the MOSFET is first turned
off (which should make the output voltage drop). This is
because the gate going low causes the drain to go low
momentarily due to c
, which in turn causes V
to go
low, making the output rise. The extra R9 and C11 in the
gate drive for the MOSFET are there to slow down the
slew rate of the gate voltage, thus avoiding this problem.
Determining what circuit to use depends upon the ratio
between V
and V
, since the goal is to avoid
inadvertently tripping the over-voltage protection.
If:
16
.
<
V
V
)
LOW
(
OUT
)
HIGH
(
OUT
This means that the ratio is less than the worst-case
OVP threshold (worst-case in this case is the lowest
threshold), then the direct drive (simplest) method may
be used. Of course the indirect drive method may also
be used if desired.
If:
16
.
V
V
)
LOW
(
OUT
)
HIGH
(
OUT
>
This means that the ratio is greater than the worst-case
OVP threshold, therefore we automatically need to slew
the rate of change, and the indirect drive method
must
be used.
If using the indirect drive method, the goal is to slow
down the gate drive for the transition from V
to
V
, which is when the external MOSFET is turned
off. The pull-up resistor, pull-down resistor and gate
capacitor can be selected as follows:
1) V
must be below the gate threshold voltage of the
MOSFET in order to ensure that it can be turned off (see
Figure 6):
2) The RC time constant of R9 and C11 should be at
least 4 times greater than the typical Over-Voltage Fault
Delay Time of 5μs to avoid V
rising prior to falling.
3) V
PULLUP
must be high enough to turn the MOSFET on.
Figure 6: Ensuring Q3 Will Turn Off
R3
20k0
0402
R7
20k0
0402
EN/PSV
TON
VOUT
VCCA
FB
PGD
VSSA
PGND
DL
VDDP
ILIM
LX
DH
BST
U1
SC470
VOUT
0402
C5
56p
R5
49k9
0402
Low = 1.0V
High = 1.2V
Open Drain Signal
Q3
R8
pull-up
C11
R9
R3
20k0
0402
R7
20k0
0402
EN/PSV
TON
VOUT
VCCA
FB
PGD
VSSA
PGND
DL
VDDP
ILIM
LX
DH
BST
U1
SC470
VOUT
C5
56p
0402
R5
49k9
0402
Open Drain Signal
Low = 1.2V
High = 1.0V
Q3
R8
pull-up
C11
R9
VGATE
VPULLUP
(
)
)
TH
(
GS
PULLUP
9
R
+
V
8
R
V
9
R
<
相關(guān)PDF資料
PDF描述
SC471EVB Synchronous Buck Controller with Multi-Level VOUT Transition Support
SC471MLTRT Synchronous Buck Controller with Multi-Level VOUT Transition Support
SC471 Synchronous Buck Controller with Multi-Level VOUT Transition Support
SC471A Synchronous Buck Controller with Multi-Level VOUT Transition Support
SC471AMLTRT Synchronous Buck Controller with Multi-Level VOUT Transition Support
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
SC471 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller with Multi-Level VOUT Transition Support
SC471_08 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller with Multi-Level VOUT Transition Support
SC471A 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller with Multi-Level VOUT Transition Support
SC471AEVB 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller with Multi-Level VOUT Transition Support
SC471AMLTRT 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:Synchronous Buck Controller with Multi-Level VOUT Transition Support
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