参数资料
| 型号： | SC4508AMLTRT |
| 厂商： | Semtech |
| 文件页数： | 10/21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
I Cin = I o D [( 1 +
)( 1 ?
) + 2 ( 1 ? D ) ]
? v ESR = R esr ( 1 + ) I dc
? v C ≈
Application Information (Cont.)
Req and Ceq are both functions of frequency. For rigorous
design, the equivalent ESR should be evaluated at the
ripple frequency for voltage ripple calculation when both
ceramic and electrolytic capacitors are used. If R 1a = R 1b
= R 1 and C 1a = C 1b = C 1 , then R eq and C eq will be frequency-
independent and
R eq = 1/2 R 1 and C eq = 2C 1
Input Capacitor (C in )
The input supply to the converter usually comes from a
pre-regulator. Since the input supply is not ideal, input
capacitors are needed to filter the current pulses at the
switching frequency. A simple buck converter is shown in
Figure 3.
Figure 3. A simple model for the converter input
In Figure 3 the DC input voltage source has an internal
impedance R in and the input capacitor C in has an ESR of
R esr . MOSFET and input capacitor current waveforms, ESR
voltage ripple and input voltage ripple are shown in Figure
4.
It can be seen that the current in the input capacitor
pulses with high di/dt. Capacitors with low ESL should be
used. It is also important to place the input capacitor
close to the MOSFETs on the PC board to reduce trace
inductances around the pulse current loop.
The RMS value of the capacitor current is approximately
δ 2 D 2 D
12 η η
The power dissipated in the input capacitors is then:
P Cin = I Cin2 R esr
For reliable operation , the maximum power dissipation
in the capacitors should not result in more than 10 o C of
temperature rise. Many manufacturers specify the
maximum allowable ripple current (RMS) rating of the
capacitor at a given ripple frequency and ambient
temperature. The input capacitance should be high
enough to handle the ripple current. For higher power
applications, multiple capacitors are placed in parallel to
increase the ripple current handling capability.
Sometimes meeting tight input voltage ripple
specifications may require the use of larger input
capacitance. At full load, the peak-to-peak input voltage
ripple due to the ESR is:
δ
2
The peak-to-peak input voltage ripple due to the capacitor
is:
DI dc
C in f s
From these two expressions, C IN can be found to meet
the input voltage ripple specification.
Power MOSFETs Selection
Main considerations in selecting the MOSFETs are power
dissipation, cost and packaging. Switching losses and
conduction losses of the MOSFETs are directly related to
the total gate charge ( C g ) and channel on-resistance
( R ds(on) ). In order to judge the performance of MOSFETs,
the product of the total gate charge and on-resistance is
used as a figure of merit (FOM). Transistors with the same
FOM follow the same curve in Figure 5.
Figure 4. Typical waveforms at converter input.
? 2007 Semtech Corp.
10
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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