参数资料
| 型号： | SC4503TSKTRT |
| 厂商： | Semtech |
| 文件页数： | 9/22页 |
| 文件大小： | 0K |
| 描述： | IC REG BOOST ADJ 1.4A TSOT23-5 |
| 标准包装： | 1 |
| 类型： | 升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 可调至 27V |
| 输入电压： | 2.5 V ~ 20 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 1.3MHz |
| 电流 - 输出： | 1.4A |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | SOT-23-5 细型，TSOT-23-5 |
| 包装： | 标准包装 |
| 供应商设备封装： | TSOT-23-5 |
| 产品目录页面： | 1358 (CN2011-ZH PDF) |
| 其它名称： | SC4503TSKDKR |
SC4503
POWER MANAGEMENT
+
+
Applications Information (Cont.)
Duty Cycle
The duty cycle D of a boost converter in continuous-conduc-
tion mode (CCM) is:
?
= (3)
?
where V CESAT is the switch saturation voltage and V D is volt-
age drop across the rectifying diode.
where I LIM is the switch current limit.
It is worth noting that I OUTMAX is directly proportional to the
ratio and that switching losses are neglected in its
derivation. Equation (4) therefore over-estimates the
maximum output current, however it is a useful ? rst-order
approximation.
Using V CESAT = 0.3V, V D = 0.5V and I LIM =1.4A in (3) and (4),
the maximum output current for three V IN and V OUT combi-
nations are tabulated (Table 1).
Maximum Output Current
In a boost switching regulator the inductor is connected
to the input. The inductor DC current is the input current.
When the power switch is turned on, the inductor current
V IN (V)
3.3
3.3
5
V OUT (V)
12
5
12
D
0.754
0.423
0.615
I OUT (A)
0.34
0.80
0.53
? ows into the switch. When the power switch is off, the
inductor current ? ows through the rectifying diode to the
output. The output current is the average diode current.
The diode current waveform is trapezoidal with pulse width
(1 – D)T (see Figure 4). The output current available from
Table 1. Calculated Maximum Output Currents
Maximum Duty-Cycle Limitation
The power transistor in the SC4503 is turned off every
Inductor
I IN
switching period for 80ns. This minimum off time limits the
maximum duty cycle of the regulator. A boost converter with
Current
ON
OFF
ON
Switch Current
high
ratio requires long switch on time and high duty
0
Diode Current
cycle. If the required duty cycle is higher than the attain-
able maximum, then the converter will operate in dropout.
DT
(1-D)T
I OUT
(Dropout is a condition in which the regulator cannot attain
its set output voltage below current limit.)
ON
OFF
ON
OFF
ON
0
Figure 4. Current Waveforms in a Boost Converter
a boost converter therefore depends on the converter oper-
ating duty cycle. The power switch current in the SC4503 is
internally limited to at least 1.4A. This is also the maximum
peak inductor or the peak input current. By estimating the
conduction losses in both the switch and the diode, an
expression of the maximum available output current of a
boost converter can be derived:
Note: dropout can occur when operating at low input volt-
ages (<3V) and with off times approaching 100ns. Shorten
the PCB trace between the power source and the device
input pin, as line drop may be a signi ? cant percentage of
the input voltage. A regulator in dropout may appear as
if it is in current limit. The cycle-by-cycle current limit of
the SC4503 is duty-cycle and input voltage invariant and
should be at least 1.4A. If the converter output is below
its set value and switch current limit is not reached (1.4A),
then the converter is likely in dropout.
=
?
?
?
(
?
)
(4)
Example : Determine the highest attainable output voltage
when boosting from a single Li-ion cell.
Equation (3) can be re-arranged as:
? 2007 Semtech Corp.
9
www.semtech.com
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| SC4503WLTRT | 功能描述:IC REG BOOST ADJ 1.4A 8MLPD RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
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| SC4505_07 | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:High Efficiency Boost Converter for Backlight/Flash LED Driver |
| SC4505EVB | 制造商:SEMTECH 制造商全称:Semtech Corporation 功能描述:High Efficiency Boost Converter for Backlight/Flash LED Driver |
| SC4505EVB-1 | 制造商:Semtech Corporation 功能描述:EVALUATION BOARD |
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