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參數(shù)資料
| 型號(hào)： | 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)： | 20/37頁 |
| 文件大?。?/td> | 1024K |
| 代理商： | SC2441ATETRT |
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20
2006 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
Applications Information
SC2441A
Operating Frequency (f
s
)
The switching frequency in the SC2441A is user-
programmable. The advantages of constant frequency
operation are simple passive component selection and
fast transient response with simple frequency
compensation. Before setting the operating frequency,
the following trade-offs should be considered.
1) passive component sizes
2) converter efficiency
3) EMI
4) Minimum switch on time and
5) Maximum duty ratio
For a given output power, the sizes of the passive
components are inversely proportional to the switching
frequency, whereas MOSFET’s/Diodes switching losses
are proportional to the operating frequency. Other issues
such as heat dissipation, packaging and the cost issues
should be considered. The frequency bands for signal
transmission should be avoided because of EM
interference.
The switching frequency of both step-down controllers is
set with an external resistor from Pin 10 to the signal
ground. The set frequency is inversely proportional to the
resistor value (Figure 7) and can be approximated as:
1.22
SW
OSC
F
101618
R
R
OSC
is in K
and F
SW
is in KHz.
The internal oscillator starts to operate once V
exceeds
its UVLO threshold. The oscillator output, CLK, (see Figure
2) clocks the step-up converter. The frequency divider
generates two out-of-phase clocks, CLK1 and CLK2, at
a half of CLK frequency. CLK1 and CLK2 clock the step-
down channels. The switching frequency of the step-up
converter is twice those of the step-down controllers. If
both step-down channels are running at 250KHz, then
the boost section will be running at 500KHz.
Rosc vs Single Channel Switching Frequency
R
OSC
vs. Step-down Channel Switching Frequency
10
30
50
70
90
110
130
150
100
300
500
700
900
1100
Switching Frequency (KHz)
R
O
)
Figure 7. R
OSC
vs. Step-down Channel Free-running
Frequency
Minimum Switch On Time Limitation
In both step-down controllers, the falling edge of the
clock turns on the top MOSFET. The inductor current
ramps up so does the sensed voltage. After the sensed
voltage crosses a threshold determined by the error
amplifier output, the top MOSFET is turned off. The
propagation delay time from the turn-on of the controlling
FET to its turn-off is the minimum switch on time. The
SC2441A has a minimum on time of about 180ns at
room temperature. This is the shortest on interval of the
controlling FET. The controller either does not turn on
the top MOSFET at all or turns it on for at least 180ns.
For a synchronous step-down converter, the operating
duty cycle is V
/V
IN
. So the required on time for the top
MOSFET is V
/(V
f
). If the frequency is set such that the
required pulse width is less than 180ns, then the
converter will start skipping cycles. Due to minimum on
time limitation, simultaneously operating at very high
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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