参数资料
| 型号： | SC2446ITETRT |
| 厂商： | Semtech |
| 文件页数： | 17/38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.)
The conduction losses are then
P bc =I Q2,rms2 R ds(on) .
where R ds(on) is the channel resistance of bottom MOSFET.
If the input voltage to output voltage ratio is high (e.g.
V in =12V, V o =1.5V), the duty ratio D will be small. Since the
bottom switch conducts with duty ratio (1-D), the
corresponding conduction losses can be quite high.
Due to non-overlapping conduction between the top and
the bottom MOSFET’s, the internal body diode or the
external Schottky diode across the drain and source
terminals always conducts prior to the turn on of the bottom
MOSFET. The bottom MOSFET switches on with only a diode
voltage between its drain and source terminals. The
switching loss
P bs = 21 ( t r + t f )( 1 + 2 δ ) I o V d f s
is negligible due to near zero-voltage switching.
The gate losses are estimated as
Integrated Power MOSFET Drivers
In SC2446 there are four internally integrated gate
drivers to drive all the MOSFETs in dual channels. With
the device bipolar process, emitter-follower based
Darlington bipolar transistors are used for the output
stage. The key advantage of the Darlington configuration
is that the total current gain is greatly improved which
leads to larger driving current I gs . This in turn will help
reduce the MOSFETs switching losses. In order to
estimate the losses associated with the gate driver, we
first measured the gate driver waveform (typical
waveforms of V ce and I gs ) as shown in Figure12.
P bg =
R g
R gt
Q g V cc f s .
The total bottom switch losses are then
T j , max ? T a , max
?
1 t 2
v ce ( t ) = V cc 2
.
P b =P bc +P bs +P bg .
Once the power losses P loss for the top (P t ) and bottom (P b )
MOSFET’s are known, thermal and package design at
component and system level should be done to verify that
the maximum die junction temperature (T j,max , usually
125 o C) is not exceeded under the worst-case condition.
The equivalent thermal impedance from junction to
ambient ( θ ja ) should satisfy
θ ja ≤ .
P loss
θ ja depends on the die to substrate bonding, packaging
material, the thermal contact surface, thermal compound
property, the available effective heat sink area and the air
flow condition (free or forced convection). Actual temperature
measurement of the prototype should be carried out to
verify the thermal design.
Figure 12. Measured gate driver output waveforms
with 2.2 ? current limit resistor.
It is clear that the saturation voltage is not a constant. It
changes with the driving current in a nonlinear fashion.
A simple formula to calculate the losses with a reasonable
accuracy is not available. But, we use a curve fitting
technique to estimate the power losses in gate driver.
First, the saturation voltage v ce (t) is approximated as
( )
2 T 1
Where, V cc is the gate driver collector voltage, T 1 is a time
constant related to the fall time of v ce . For the example
in Fig. 12, V cc =12V, T 1 =0.5T f with T f being measured as
~50 ns. With these parameters, the approximated v ce (t) is
plotted as in Figure 13 a).
? 2004 Semtech Corp.
17
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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