参数资料
| 型号： | SC2446ITETRT |
| 厂商： | Semtech |
| 文件页数： | 12/38页 |
| 文件大小： | 0K |
| 描述： | IC SYNC STEP DOWN CTRLR 28-TSSOP |
| 标准包装： | 1 |
| 应用： | 控制器，DDR |
| 输入电压： | 4.7 V ~ 16 V |
| 输出数： | 2 |
| 输出电压： | 可调至 0.5V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.173"，4.40mm 宽）裸露焊盘 |
| 供应商设备封装： | 28-TSSOP 裸露焊盘 |
| 包装： | 标准包装 |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC2446ITEDKR |
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SC2446
POWER MANAGEMENT
Application Information (Cont.)
Setting the Switching Frequency
The switching frequency is set with an external resistor
connected from Pin 3 to the ground. The set frequency
is inversely proportional to the resistor value (Figure 5).
800
700
600
500
400
300
200
100
0
The followings are to be considered when choosing
inductors.
a) Inductor core material: For high efficiency applications
above 350KHz, ferrite, Kool-Mu and polypermalloy
materials should be used. Low-cost powdered iron cores
can be used for cost sensitive-applications below 350KHz
but with attendant higher core losses.
b) Select inductance value: Sometimes the calculated
inductance value is not available off-the-shelf. The
designer can choose the adjacent (larger) standard
inductance value. The inductance varies with
temperature and DC current. It is a good engineering
practice to re-evaluate the resultant current ripple at
the rated DC output current.
c) Current rating: The saturation current of the inductor
should be at least 1.5 times of the peak inductor current
under all conditions.
0
50
100 150
Rosc (k Ohm)
200
250
Output Capacitor (C o ) and V out Ripple
The output capacitor provides output current filtering in
V o ( 1 ? D )
di b ( t )
1
∫
C o 0
Figure 5. Free running frequency vs. R OSC .
Inductor (L) and Ripple Current
Both step-down controllers in the SC2446 operate in
synchronous continuous-conduction mode (CCM) regardless
of the output load. The output inductor selection/design
is based on the output DC and transient requirements.
Both output current and voltage ripples are reduced with
larger inductors but it takes longer to change the inductor
current during load transients. Conversely smaller inductors
results in lower DC copper losses but the AC core losses
(flux swing) and the winding AC resistance losses are
higher. A compromise is to choose the inductance such
that peak-to-peak inductor ripple-current is 20% to 30% of
the rated output load current.
Assuming that the inductor current ripple (peak-to-peak)
value is δ * I o , the inductance value will then be
L = .
δ I o f s
The peak current in the inductor becomes (1+ δ /2)*Io
and the RMS current is
steady state and serves as a reservoir during load transient.
The output capacitor can be modeled as an ideal capacitor
in series with its parasitic ESR ( R esr ) and ESL ( L esl ) (Figure
6).
Co
Lesl
Resr
Figure 6. An equivalent circuit of C o .
If the current through the branch is i b (t), the voltage across
the terminals will then be
t
v o ( t ) = V o + i b ( t ) dt + L esl + R esr i b ( t ).
dt
This basic equation illustrates the effect of ESR, ESL and
C o on the output voltage.
I L , rms = I o 1 +
δ 2
12
.
The first term is the DC voltage across C o at time t=0 . The
second term is the voltage variation caused by the charge
balance between the load and the converter output. The
? 2004 Semtech Corp.
12
www.semtech.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| SC2446ITSTRT | 制造商:Semtech Corporation 功能描述:Controller IC 制造商:Semtech Corporation 功能描述:SC Series 4.7 to 16 V 1 MHz Dual-Phase Synchronous Step-Down Controller TSSOP-28 |
| SC2447 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase, Single or Dual Output Synchronous Step-Down Controller |
| SC24-470-R | 功能描述:INDUCTOR SHIELD 47UH 150MA SMD RoHS:是 类别:电感器，线圈，扼流圈 >> 固定式 系列:SC24 标准包装:500 系列:1331 电感:1.2µH 电流:247mA 电流 - 饱和:247mA 电流 - 温升:- 类型:铁芯体 容差:±10% 屏蔽:屏蔽 DC 电阻(DCR):最大 730 毫欧 Q因子@频率:40 @ 7.9MHz 频率 - 自谐振:130MHz 材料 - 芯体:铁 封装/外壳:0.312" L x 0.115" W x 0.135" H（7.94mm x 2.92mm x 3.43mm） 安装类型:表面贴装 包装:带卷 (TR) 工作温度:-55°C ~ 105°C 频率 - 测试:7.9MHz |
| SC24-471-R | 功能描述:INDUCTOR SHIELD 470UH 50MA SMD RoHS:是 类别:电感器，线圈，扼流圈 >> 固定式 系列:SC24 标准包装:500 系列:1331 电感:1.2µH 电流:247mA 电流 - 饱和:247mA 电流 - 温升:- 类型:铁芯体 容差:±10% 屏蔽:屏蔽 DC 电阻(DCR):最大 730 毫欧 Q因子@频率:40 @ 7.9MHz 频率 - 自谐振:130MHz 材料 - 芯体:铁 封装/外壳:0.312" L x 0.115" W x 0.135" H（7.94mm x 2.92mm x 3.43mm） 安装类型:表面贴装 包装:带卷 (TR) 工作温度:-55°C ~ 105°C 频率 - 测试:7.9MHz |
| SC2447EVB | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:Dual-Phase, Single or Dual Output Synchronous Step-Down Controller |
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