参数资料
| 型号： | SC4508AMLTRT |
| 厂商： | Semtech |
| 文件页数： | 11/21页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST INV PWM 12-MLPQ |
| 标准包装： | 1 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1.5MHz |
| 占空比： | 97% |
| 电源电压： | 2.7 V ~ 15 V |
| 降压： | 是 |
| 升压： | 是 |
| 回扫： | 无 |
| 反相： | 是 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 12-VQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC4508AMLDKR |
SC4508A
POWER MANAGEMENT
Application Information (Cont.)
50
40
Cg ( 100 , Rds )
manufacturers ’ data sheet. From the FDS6675
datasheet, R ds(on) is less than 14m ? when V gs is greater
than 10V. However R ds(on) increases by 30% as the
junction temperature increases from 25 o C to 110 o C.
Cg ( 200 , Rds )
Cg ( 500 , Rds )
20
The switching losses can be estimated using the simple
formula:
r
f
1
0
0
1
5 10 15
Rds
On-resistance (mOhm)
FOM:100*10^{-12}
FOM:200*10^{-12}
FOM:500*10^{-12}
20
20
P ts = 21 ( t r + t f )( 1 + 2 δ ) I dc V in f s
where t r is the rise time and t f is the fall time of the
switching process. Different manufacturers have
different definitions and test conditions for t and t . To
clarify these, we sketch the typical MOSFET switching
characteristics under clamped inductive mode in Figure
current to reach its full-scale value I ds and
Q gd is the charge needed to charge gate-to-drain (Miller)
I Qrms = I dc D ( 1 + 12 )
δ
t r =
Figure 5. Figure of Merit curves.
The closer the curve is to the origin, the lower is the FOM.
This means lower switching loss or lower conduction loss
or both. It may be difficult to find MOSFETs with both low
C g and low R ds(on . Usually a trade-off between R ds(on and
C g has to be made.
MOSFET selection also depends on applications. In many
applications, either switching loss or conduction loss
dominates for a particular MOSFET. For buck and buck-
boost converters with high input to output voltage ratios,
the MOSFET is hard switched but conducts with very low
duty cycle. For such applications, MOSFETs with low C g
should be used.
MOSFET power dissipation consists of:
a) conduction loss due to the channel resistance R ds(on) ,
b) switching loss due to the switch rise time t r and fall
time t f , and
c) the gate loss due to the gate resistance R G .
The RMS value of the MOSFET switch current is calculated
as:
2
The conduction losses are then
P tc = I Qrms2 R ds(on)
Idc is average inductor current. In buck converter, it is
also load current. In buck-boost, it is load current divided
by 1-D.
R ds(on) varies with temperature and gate-source voltage.
Curves showing R ds(on) variations can be found in
6.
Figure 6. MOSFET switching characteristics
In Figure 6,
Q gs1 is the gate charge needed to bring the gate-to-source
voltage V gs to the threshold voltage V gs_th ,
Q gs2 is the additional gate charge required for the switch
.
capacitance when V ds is falling.
Switching losses occur during the time interval [ t 1 , t 3 ].
Defining t r = t 3 -t 1 and t r can be approximated as:
( Q gs 2 + Q gd )R gt
V cc ? V gsp
where R gt is the total resistance from the driver supply
rail to the gate of the MOSFET. It includes the gate driver
internal impedance R gi , external resistance R ge and the
gate resistance R g within the MOSFET i.e.
R gt = R gi +R ge +R g
V gsp is the Miller plateau voltage shown in Figure 11.
Similarly an approximate expression for t f is:
? 2007 Semtech Corp.
11
www.semtech.com
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| SC4509SKTRT | 功能描述:IC LED DRVR WT/OLED BCKLT SOT236 RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 标准包装:60 系列:- 恒定电流:- 恒定电压:- 拓扑:线性（LDO），PWM，升压（升压） 输出数:8 内部驱动器:是 类型 - 主要:背光 类型 - 次要:RGB，白色 LED 频率:500kHz ~ 1.5MHz 电源电压:4.75 V ~ 26 V 输出电压:45V 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* 工作温度:-40°C ~ 85°C |
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