参数资料
| 型号： | SC2446ITETRT |
| 厂商： | Semtech |
| 文件页数： | 13/38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.)
third term is voltage ripple due to ESL and the fourth
term is the voltage ripple due to ESR. The total output
should be an order of magnitude smaller than the voltage
ripple caused by the ESR. To guarantee this, the
capacitance should satisfy
voltage ripple is then a vector sum of the last three
terms.
C o >
10
2 π f s R esr
.
? v C ≈
δ I o
Since the inductor current is a triangular waveform with
peak-to-peak value δ * I o , the ripple-voltage caused by
inductor current ripples is
,
8 C o f s
the ripple-voltage due to ESL is
In many applications, several low ESR ceramic capacitors
are added in parallel with the aluminum capacitors in
order to further reduce ESR and improve high frequency
decoupling. Because the values of capacitance and ESR
are usually different in ceramic and aluminum capacitors,
the following remarks are made to clarify some practical
? v ESL = L esl f s
δ I o
D
,
issues.
Remark 1: High frequency ceramic capacitors may not carry
and the ESR ripple-voltage is
? v ESR = R esr δ I o .
Aluminum capacitors (e.g. electrolytic, solid OS-CON,
POSCAP, tantalum) have high capacitances and low ESL’s.
The ESR has the dominant effect on the output ripple
voltage. It is therefore very important to minimize the ESR.
When determining the ESR value, both the steady state
ripple-voltage and the dynamic load transient need to be
considered. To keep the steady state output ripple-voltage
< ? V o , the ESR should satisfy
most of the ripple current. It also depends on the capacitor
value. Only when the capacitor value is set properly, the
effect of ceramic capacitor low ESR starts to be significant.
For example, if a 10 μ F, 4m ? ceramic capacitor is
connected in parallel with 2x1500 μ F, 90m ? electrolytic
capacitors, the ripple current in the ceramic capacitor is
only about 42% of the current in the electrolytic capacitors
at the ripple frequency. If a 100 μ F, 2m ? ceramic capacitor
is used, the ripple current in the ceramic capacitor will be
about 4.2 times of that in the electrolytic capacitors. When
two 100 μ F, 2m ? ceramic capacitors are used, the current
ratio increases to 8.3. In this case most of the ripple
current flows in the ceramic decoupling capacitor. The ESR
R esr 1 <
? V o
δ I o
.
of the ceramic capacitors will then determine the output
ripple-voltage.
α V o
To limit the dynamic output voltage overshoot/undershoot
within α (say 3%) of the steady state output voltage) from
no load to full load, the ESR value should satisfy
R esr 2 < .
I o
Then, the required ESR value of the output capacitors
Remark 2: The total equivalent capacitance of the filter
bank is not simply the sum of all the paralleled capacitors.
The total equivalent ESR is not simply the parallel
combination of all the individual ESR’s either. Instead they
should be calculated using the following formulae.
( R 1 a + R 1 b ) 2 ω 2 C 1 a C 1 b + ( C 1 a + C 1 b ) 2
( R 1 a C 1 a + R 1 b C 1 b ) ω 2 C 1 a C 1 b + ( C 1 a + C 1 b )
should be
R esr = min{R esr1 ,R esr2 }.
C eq ( ω ) : =
2 2
2 2
The voltage rating of aluminum capacitors should be at
δ I o
R 1 a R 1 b ( R 1 a + R 1 b ) ω 2 C 1 a C 1 b + ( R 1 b C 1 b + R 1 a C 1 a )
least 1.5 V o . The RMS current ripple rating should also be
greater than
.
2 3
Usually it is necessary to have several capacitors of the
same type in parallel to satisfy the ESR requirement. The
voltage ripple cause by the capacitor charge/discharge
2 2 2 2
R eq ( ω ) : = 2 2
( R 1 a + R 1 b ) 2 ω 2 C 1 a C 1 b + ( C 1 a + C 1 b ) 2
where R 1a and C 1a are the ESR and capacitance of
electrolytic capacitors, and R 1b and C 1b are the ESR and
capacitance of the ceramic capacitors respectively. (Figure
7)
? 2004 Semtech Corp.
13
www.semtech.com
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相关代理商/技术参数 |
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| 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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