参数资料
| 型号： | SC2440TETRT |
| 厂商： | Semtech |
| 文件页数： | 13/26页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 2A DL 16TSSOP |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出数： | 2 |
| 输入电压： | 2.8 V ~ 20 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.4MHz |
| 电流 - 输出： | 2A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 16-TSSOP |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC2440TEDKR |
SC2440
POWER MANAGEMENT
Applications Information
results from the ESR of the output capacitor while the
second term is due to the charging and discharging of
C OUT by the inductor ripple current. Substituting ? I L = 0.6A,
f = 1MHz and C OUT = 10 μ F ceramic with ESR = 3m ? in
(7),
? V OUT = 0 . 6 A ? ( 3 m ? + 12 . 5 m ? )
= 1 . 8 mV + 7 . 5 mV = 9 . 3 mV
Depending on operating frequency and the type of
capacitor, ripple voltage resulting from charging and
discharging of C OUT may be higer than that due to ESR. A
10 μ F or 22 μ F X5R ceramic capacitor is found adequate
for output filtering in most applications. Ripple current
in the output capacitor is not a concern because the
inductor current of a buck converter directly feeds C OUT ,
resulting in very low ripple current. Avoid using Z5U and
Y5V ceramic capacitors for output filtering because these
types of capacitors have high temperature and high
voltage coefficients.
Freewheeling Diode
Use of Schottky barrier diodes as freewheeling rectifiers
reduces diode reverse recovery input current spikes,
easing high-side current sensing in the SC2440. These
diodes should have a RMS current rating between 1A
and 2A and a reverse blocking voltage of at least 5V
higher than the input voltage. For switching regulators
operating at low duty cycles (i.e. low output voltage to
input voltage conversion ratios), it is beneficial to use
freewheeling diodes with somewhat higher RMS current
ratings (thus lower forward voltages). This is because the
diode conduction interval is much longer than that of
the transistor. Converter efficiency will be improved if
the voltage drop across the diode is lower.
The freewheeling diodes should be placed close to the
SW pins of the SC2440 to minimize ringing due to trace
inductance. Surface-mount equivalents of 1N5817 and
1N5819, MBRM120LT3 (ON Semi), UPS120 and
UPS140 (Micro-Semi) are all suitable.
higher in voltage than V IN . The required driver supply
voltage (at least 2.5V higher than the SW voltage over
the industrial temperature range) is generated with a
bootstrap circuit (the diode D BST and the capacitor C BST in
Figure 8). The bootstrapped output (the common node
between D BST and C BST ) is connected to the BOOST pin of
the SC2440. The power transistor in the SC2440 is first
switched on to build up current in the inductor. When
the transistor is switched off, the inductor current pulls
the SW node low, allowing C BST to be charged through
D BST . When the power switch is again turned on, the SW
voltage goes high. This brings the BOOST voltage to
V SW + V C BST , thus back-biasing D BST . C BST voltage increases
with each subsequent switching cycle, as does the
bootstrapped voltage at the BOOST pin. After a number
of switching cycles, C BST will be fully charged to a voltage
approximately equal to that applied to the anode of D BST .
Figure 7 shows the typical minimum BOOST to SW voltage
required to fully saturate the power transistor. This
differential voltage ( = V C BST ) must be at least 1.8V at
room temperature. This is also specified in the “Electrical
Characteristics” as “Minimum Bootstrap Voltage”. The
minimum required V C BST increases as temperature
decreases. The bootstrap circuit reaches equilibrium
when the base charge drawn from C BST during transistor
on time is equal to the charge replenished during the off
interval.
Minimum Bootstrap Voltage
vs Temperature
2.4
2.2
2.0
1.8
1.6
Bootstrapping the Power Transistors
1.4
-50
-25
0
25
50
75
100
To maximize efficiency, the turn-on voltage across the
internal power NPN transistors should be minimized. If
these transistors are to be driven into saturation, then
their bases will have to be driven from a power supply
Temperature (°C)
Figure 7. Typical Minimum Bootstrap Voltage Re-
quired to Maintain Saturation at I SW = 2A.
? 2005 Semtech Corp.
13
www.semtech.com
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| SC2441 | 制造商:SEMTECH 制造商全称: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 制造商全称:Semtech Corporation 功能描述:1.8V to 20V Input 2-Phase Synchronous Step-down Controllers with Step-up Converter |
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| SC2441AEVB | 制造商:SEMTECH 制造商全称: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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