參數(shù)資料
型號(hào)： 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(yè)數(shù)： 15/26頁(yè)
文件大小： 643K
代理商： SC2440TETRT
15
2005 Semtech Corp.
www.semtech.com
SC2440
POWER MANAGEMENT
Applications Information
loss of
β
OUT
SW
V
DI
.
Since V
< V
, D
should always be tied to V
(if
>2.5V) to maximize efficiency. Measurement of the 2-
channel regulator in Figure 1 shows that the efficiency
penalties are about 1.3% (V
= 5V) and 2.2% (V
=
3.3V) with input bootstrapping. In general efficiency
penalty increases as D decreases.
Figure 8 summarizes various ways of bootstrapping the
SC2440. A fast switching PN diode (such as 1N4148 or
1N914) and a small (0.1μF – 0.47μF) ceramic capacitor
can be used. In Figure 8(a) the power switch is
bootstrapped from the output. This is the most efficient
configuration and it also results in the least voltage stress
at the BOOST pin. The maximum BOOST pin voltage is
about
OUT
V
+
. If the output is below 2.8V, then D
BST
will preferably be a small Schottky diode (such as BAT-
54) to maximize bootstrap voltage. A 0.33-0.47μF
bootstrap capacitor may be needed to reduce droop.
Bench measurement shows that using Schottky
bootstrapping diode has no noticeable efficiency benefit.
IN
V
The SC2440 can also be bootstrapped from the input
(Figure 8(b)). This configuration is not as efficient as Figure
8(a). However this may be only option if the output
voltage is less than 2.5V and there is no other supply
with voltage higher than 2.5V. Voltage stress at the
BOOST pin can be somewhat higher than 2V
IN
. The BOOST
pin voltage should not exceed its absolute maximum
rating of 40V.
Figures 8(c) and (d) show how to bootstrap the SC2440
from a second independent power supply V
with voltage
> 2.5V. D
in Figure 8(d) prevents start up difficulty if
V
IN
comes up before V
S
.
Since the inductor current charges C
, the bootstrap
circuit requires some minimum load current to get going.
Figures 9(a) and 9(b) show the dependence of the
minimum input voltage required to properly bootstrap a
5V and a 3.3V converters on the load current. Once
started the bootstrap circuit is able to sustain itself down
to zero load.
Shutdown and Soft-Start
Each regulating channel of the SC2440 has its own soft-
start circuit. Pulling its soft-start pin below 0.8V with an
open-collector NPN or an open-drain NMOS transistor
turns off the corresponding regulator. The other regulator
continues to operate. With one channel turned off, the
internal bias circuit is kept alive. In the “Typical
Characteristics”, the soft-start pin current is plotted
against the soft-start voltage with V
IN
= 5V. When one of
Figure 9. Minimum Input Voltage Required to Start and to Maintain Bootstrap.(T
A
= 25
°
C).
Minimum Starting and
Sustaining V
IN
vs Load Current
4.5
5.0
5.5
6.0
6.5
7.0
7.5
1
10
100
1000
Load Current (mA)
M
D
BST
TIED
TO OUTPUT
D
TIED
TO INPUT
V
OUT
= 5V
MA729
STARTING
SUSTAINING
(a)
(b)
Minimum Starting and
Sustaining V
IN
vs Load Current
3.5
4.0
4.5
5.0
5.5
0.1
1.0
10.0
100.0
1000.0
Load Current (mA)
M
D
BST
TIED
TO OUTPUT
D
TIED
TO INPUT
V
OUT
= 3.3V
MA729
STARTING
SUSTAINING
相關(guān)PDF資料
PDF描述
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SC2441AEVB 1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter
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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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