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參數(shù)資料
| 型號： | SC2440TETRT |
| 廠商： | Semtech Corporation |
| 英文描述： | 2.5 MHz Dual Switching Regulator with Integrated 2A Switches |
| 中文描述： | 2.5 MHz雙開關(guān)穩(wěn)壓器集成甲開關(guān) |
| 文件頁數(shù)： | 11/26頁 |
| 文件大?。?/td> | 643K |
| 代理商： | SC2440TETRT |
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11
2005 Semtech Corp.
www.semtech.com
SC2440
POWER MANAGEMENT
Applications Information
output voltage will not be able to reach its set value in
continuous-conduction mode.
Example
:
Determine the maximum operating frequency
of a dual 3.3V to 1.8V and 3.3V to 2.5V switching
regulator using the SC2440.
Assuming that V
D
= 0.45V, V
CESAT
= 0.25V and V
IN
= 2.97V
(10% low line), the duty ratios
and 2.5V converters can be calculated using (2).
1
D
and
2
D
of the 1.8V
71
.
25
.
45
.
97
.
45
.
8
+
D
1
=
+
=
93
.
25
.
45
.
97
.
45
.
5
+
D
2
=
+
=
.
The maximum operating frequencies of the 1.8V and the
2.5V converters are therefore
MHz
4
ns
120
D
1
1
=
and
KHz
580
ns
120
D
1
2
=
respectively.
Transient headroom requires that channel frequency be
lower than 580KHz.
External Synchronization
The SYNC input buffer is positive-edge triggered and TTL-
compatible (
V
8
V
IL
<
and
master oscillator generates a periodic sawtooth ramp
between two threshold voltages. A faster external clock
applied to the SYNC pin discharges the internal ramp
before it reaches its upper threshold, thus locking the
internal oscillator. As shown in Figure 2, the master
oscillator is being synchronized not the individual phases
(see Figure 2). The synchronizing frequency should be
twice
the desired
channel
frequency. Bench test shows
that an external clock with frequency ranging from slightly
below twice to at least 3.5 times the
running frequency is capable of locking the master
oscillator. To ensure frequency locking, the external clock
frequency should be at least
running
channel
frequency. The frequency of the
synchronizing clock should not be higher than 1.6 times
V
2
V
IH
>
). The free-running
channel
free-
twice
the
highest
free-
the set frequency of master oscillator because the
amplitudes of the internal sawtooth ramp and slope
compensation ramp will both be significantly reduced.
Example: Choose the value of R
to externally
synchronize the SC2440 to 2MHz per
channel
.
The required synchronizing clock frequency = 2 times
the channel frequency = 4MHz.
For a given R
, the free-running
has a tolerance of ±15%.
channel
frequency
Set the nominal free-running
MHz
2
=
to ensure locking.
channel
frequency to
MHz
73
.
15
.
Looking up the graph “Channel Frequency vs. R
” in
the Typical Characteristics, R
OSC
= 9.31K
for a set
frequency of 1.73MHz.
With ±15% tolerance, the set channel frequency can vary
from
(
)
MHz
47
.
73
.
85
.
=
Therefore
to
(
.
)
MHz
2
73
15
.
=
.
36
.
=
47
.
2
Frequency
running
Free
Lowest
Frequency
ing
Synchroniz
=
.
Inductor Selection
The inductor ripple current
I
for a non-synchronous
step-down converter in continuous-conduction mode is
fL
)
V
V
V
(
)
V
V
V
)(
+
V
V
fL
)
D
1
)(
V
V
(
I
CESAT
D
IN
CESAT
OUT
IN
D
OUT
D
OUT
L
+
=
+
=
(3)
inductance.
In current-mode control, the slope of the modulating
(sensed switch current) ramp should be steep enough
to lessen jittery tendency but not so steep that
large
flux swing decreases efficiency. Inductor ripple current
I
between 25-40% of the peak inductor current limit is
a good compromise. Inductors so chosen are optimized
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| SC2441A | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441AEVB | 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| 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 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SC2441 | 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 |
| SC2441A | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441A_09 | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441AEVB | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
| SC2441ATETRT | 制造商:Semtech Corporation 功能描述: |
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