参数资料
| 型号： | SC4508AMLTRT |
| 厂商： | Semtech |
| 文件页数： | 13/21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.)
t ssr 2 = C SS
(1 . 4 ? 0 . 9 ) V
20 μ A
When C SS = 0.1 μ F, t ssr2 is calculated as 2.5ms. Note that
during this period, the converter does not start switching
V o ( V ) 0 . 6
( 1 - h ) / h 0 . 2
R o 1 ( O h m ) 2 0 0
0 . 9
0 . 8
8 0 6
1 . 2
1 . 4
1 . 4 K
1 . 5
2
2 K
1 . 8 2 . 5 3 . 3
2 . 6 4 5 . 6
2 . 6 1 K 4 . 0 2 K 5 . 6 2 K
until SS/EN reaches 1.4V.
c) The effective start-up time is:
R o 2 ( O h m ) 1 K
1 K
1 K
1 K
1 K
1 K
1 K
t sse =
32
200 KHz
Only the voltages in boldface can be precisely set with
standard 1% resistors.
From this table, one may also observe that when the
Assuming inductor current hitting current limit for 32
cycles after SS/EN reaches 1.4V and fs=200KHz. The
average inductor current is then:
value
1 ? h
h
=
V o ? 0 . 5
0 . 5
and its multiples fall into the standard resistor value
I Leff = I LIM
t sse
t ssr 1 + t ssr 2
chart (1%, 5% or so), it is possible to use standard value
resistors to exactly set up the required output voltage
value.
R o2 =
R o1
R o2 =
R o1
–100% · (0.1 μ A) · R R /[0.5 · (R +R ) ]. To keep
this error below 0.2%, R //R < 10k ? .
I Leff ≈ 0.025 I LIM and is independent of the soft start
capacitor value. The converter will not overheat in hiccup.
Setting the Output Voltage
The non-inverting input of the error amplifier is brought
out as a device pin (Pin 9) to which the user can connect
Pin 4 or an external voltage reference. A simple voltage
divider (R o1 at top and R o2 at bottom) sets the converter
output voltage. In buck converter, the voltage feedback
gain (h=0.5/V o ) is related to the divider resistors value
as:
h
1 ? h
Once either R o1 or R o2 is chosen, the other can be
calculated for the desired output voltage V o . Since the
number of standard resistance values is limited, the
calculated resistance may not be available as a standard
value resistor. As a result, there will be a set error in the
converter output voltage. This non-random error is
caused by the feedback voltage divider ratio. It cannot
be corrected by the feedback loop.
The following table lists a few standard resistor
combinations for realizing some commonly used output
voltages.
In buck-boost converter, output voltage is set by
0.5
V O
The input bias current of the error amplifier also causes
an error in setting the output voltage. The inverting input
bias currents of error amplifiers is -100nA. Since the
non-inverting input is biased to 0.5V in buck converter,
the percentage error in the second output voltage will be
o1 o2 o1 o2
o1 o2
Loop Compensation
SC4508A is a current-mode controller. Current-mode
control is a dual-loop control system in which the inductor
peak current is loosely controlled by the inner current-
loop. The higher gain outer loop regulates the output
voltage. Since the current loop makes the inductor appear
as a current source, the complex high-Q poles of the
output LC networks is split into a dominant pole
determined by the output capacitor and the load
resistance and a high frequency pole. This pole-splitting
property of current-mode control greatly simplifies loop
compensation.
? 2007 Semtech Corp.
13
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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